ChapterPDF Available

Helium-3 in the Lunar Soil

March 2023

DOI:10.1007/978-3-031-09883-3_21

In book: Advances in Geochemistry, Analytical Chemistry, and Planetary Sciences (pp.375-396)

Authors:

E. N. Slyuta

Russian Academy of Sciences

Olga I Turchinskaya

Russian Academy of Sciences

The paper considers the mechanisms of helium implantation and concentration in minerals of lunar regolith. It is shown that the content of implanted helium is determined by the composition and structure of minerals in lunar regolith and varies in a very wide range up to three orders of magnitude or more. Amorphization of the crystal structure of ilmenite begins at energies of ions one order of magnitude higher than that of silicates and aluminosilicates and crystal lattice radiation-induced defects trap and retain helium ions much better than ones in the amorphous structure retain. Selective enrichment by solar wind ions of regolith depending on mineral composition leads to non-uniform regional distribution of helium isotope concentration and other noble gases in lunar soil. Concentration and distribution of helium isotopes in the lunar soil was studied based on direct measurements in minerals of different composition and structure, in bulk composition of regolith in areas of distribution of mare low-titanium and high-titanium basalts and Highlands’s anorthosite. Five main categories of predicted helium reserves in different geological complexes with different bulk composition of regolith and underlying rocks, different helium content and different regolith thickness were distinguished. The predicted reserves of helium isotopes in each of the categories and on the total surface of the Moon were given.

Schematic section of the structure of the loose layer of lunar regolith with a borehole in the center. Parallel shading shows the layered structure of the regolith. The underlying rocks are shown by cross-hatching. Above is a photo panorama from the Apollo 17 landing site (Credit NASA)

…

Content of He depending on the parameter (TiO 2 Â I s /FeO) [28]

…

Dependence of the implantation depth of protons and He + ions in quartz and anorthite on the ions' energy [32]: 1-implantation of protons in quartz; 2-implantation of protons in anorthite; 3-implantation of He nuclei in quartz; 4-implantation of He nuclei in anorthite

…

Protons' implantation depth and amorphization degree (disorder) in anorthite depending on protons' energy and a dose for 1 keV D = 0.96 Â 10 17 atom cm −2 , for 2 keV D = 1.3 Â 10 17 atom cm −2 , for 3 keV D = 1.6 Â 10 17 atom cm −2 : a distribution of the implanted protons' concentration; b amorphization degree (disorder) of an anorthite lattice

…

mplantation depth of He + and amorphization degree (disorder) in quartz depending on dose of D = 1 Â 10 15 atom cm −2 , D = 1 Â 10 16 atom cm −2 and D = 3.33 Â 10 16 atom cm −2 at constant energy of 12 keV: a distribution of concentration of the implanted helium; b an amorphization degree (disorder) of a quartz lattice

…

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Helium-3 in the Lunar Soil

E. N. Slyuta and O. I. Turchinskaya

1 Introduction

Ionizing irradiation by the solar wind and galactic cosmic

radiation is one of the main factors of cosmic weathering and

accumulation of cosmogenic isotopes in the lunar soil. The

study of the gross isotope composition of the solar wind has

a long history and practically began with the launching of

the ﬁrst interplanetary automatic stations at the dawn of the

space age. For the ﬁrst time, the ion component of solar wind

streams outside the Earth's magnetosphere was detected and

measured during the Luna-2 mission in September 1959.

These measurements ﬁnally conﬁrmed the hydrodynamic

theory of the solar wind proposed in 1958 by the American

physicist Eugene Parker [1], which was immediately criti-

cized by physicists.

The solar wind is formed during solar corona gasdynamic

expansion into space and is a plasma ﬂow of approximately

the same density, consisting mainly (about 95%) of electrons

and hydrogen ions (protons) [1,2]. In addition to protons,

helium ions are present in the solar wind, whose ratio to

hydrogen ions ranges from 0.037 to 0.056 [3,4]. Atoms of

Ne, Ar, Kr, and Xe and oxygen, silicon, sulfur, iron ions, etc.

are also present in small amounts. With the distance from the

Sun the solar wind velocity increases and its ﬂux density

decreases. At the Earth's orbit, its speed is about 500 km s

−1

The temperature of protons (or electrons) is about 100,000 K

and concentration 10–20 particles per cubic centimeter. The

solar wind characteristics on the Earth's orbit vary depending

on the solar activity level. The velocity of any ions is the

same, and the ion energy depends on the nucleus mass in

accordance with the hydrodynamic theory of the solar wind

propagation [1,5]. Accordingly, at the same ion velocity, the

kinetic energy of helium nuclei is 4 times greater than proton

energy. The normal proton energy on the Earth's orbit varies

from 0.3 to 3 keV, reaching 100 keV and more during solar

ﬂares.

Solar Wind Composition (SWC) experiments to study the

gross isotopic composition of the solar wind directly on the

lunar surface have been conducted since 1969 in almost all

manned Apollo missions except Apollo 17. A thin aluminum

foil measuring 30 140 cm (4000 cm

area), 15 lm thick,

and weighing 127 g for direct measurement of captured solar

wind elements was unfolded on a L-shaped support at some

angle to the lunar surface and perpendicular to the solar wind

ﬂow. The exposure time of each subsequent experiment

increased from 77 min at Apollo 11 to 45 h 05 min at

Apollo 16 [6–10]. After completing the experiment, the foil

was rolled up, placed in a container, and transported to Earth

for further study under laboratory conditions. According to

SWC experiments, the average ratio of helium isotopes

He/

He in the solar wind near the lunar surface was

2350 ±120 [11].

The study of the bulk composition of helium isotopes in

the solar wind continued in 1978–1982 in the International

Sun Earth Explorer 3 (ISEE-3) mission (the Ion Composition

Instrument (ICI)) [12,13] and in 1991–1996 in the Ulysses

mission using the Solar Wind Ion Composition Spectrometer

(SWICS) [14–16], and in the Solar and Heliospheric

Observatory (SOHO) and Advanced Composition Explorer

(ACE) missions [17,18]. Analysis of the data obtained

showed that the ratio of helium isotope ions

He/

He in the

slow and fast solar wind ﬂuxes is different and varies from

2450 to 3030 [15], while the average ratio of helium isotopes

in the outer convective zone of the Sun (in the corona and

chromosphere) is 2632 [19]. From 2001 to 2004, the Genesis

spacecraft exposed solar wind traps made of various ultra-

pure materials at the Lagrangian point L1 at a distance of 1.5

million km from Earth for 852.83 Earth days, which were

then delivered to Earth [20,21]. According to these mea-

surements, the average ratio of helium isotopes in the bulk

composition of the solar wind is 2155 [22].

E. N. Slyuta (&)O. I. Turchinskaya

Vernadsky Institute of Geochemistry and Analytical Chemistry,

Russian Academy of Sciences, 19 Kosygina St., Moscow, 119991,

Russia

e-mail: slyuta@geokhi.ru

©The Author(s), under exclusive license to Springer Nature Switzerland AG 2023

V. P. Kolotov and N. S. Bezaeva (eds.), Advances in Geochemistry, Analytical Chemistry, and Planetary Sciences,

https://doi.org/10.1007/978-3-031-09883-3_21

375

The purpose of studying the gross isotope composition of

solar wind isotopes was to estimate the average solar ele-

ment composition of matter, because due to its mass the Sun

represents 99.8% of the Solar system composition, and to

check the theory of proton-proton cycle of thermonuclear

fusion reaction in the bowels of our star on the basis of

helium isotope ratio. The study of isotopic composition of

implanted noble gases in the lunar soil besides the above

mentioned tasks allows to estimate the change of solar wind

composition since the formation of lunar rocks and regolith

and on the basis of Ar and Xe isotopic composition to

estimate the age of lunar regolith exposure on the surface

and trace the geochemical history of its formation [23]. Since

the 1986 publication of [24], helium-3 isotope has also been

considered as a possible promising source for thermonuclear

energy based on the “pure”thermonuclear reaction

D+

He = p (14.68 meV) +

He (3.67 meV), where p is a

proton [25–27]. On Earth, helium-3 is observed in trace

amounts, i.e., on the verge of its practical absence. Rare in

nature, the gas is mainly formed because of the radioactive

decay of tritium produced in nuclear reactors and during the

storage of nuclear and thermonuclear weapons. This gas is

collected in quantities of several tens of kilograms per year

and is commercially available for use in low temperature

physics and in neutron detectors used for both scientiﬁc and

security purposes [28,29].

In contrast to the Earth, helium isotopes and other noble

gases and cosmogenic isotopes have accumulated in parti-

cles and minerals of the lunar regolith throughout the geo-

logical history of the Moon because of constant irradiation

by the solar wind. Direct measurements of concentrations of

helium isotopes and other noble gases from the solar wind

trapped by regolith particles have been performed for all

regolith samples taken from different regions of the Moon by

Soviet lunar stations Luna-16, Luna-20, Luna-24, and

manned Apollo missions. The study of regolith samples

from the Apollo 11 expedition has revealed almost all basic

features of helium isotope concentration and distribution in

particles and minerals of lunar regolith, which were con-

ﬁrmed by the study of samples from other stations and

expeditions. It was found that the content and isotope ratio

of implanted helium in the lunar soil depend on the size of

the regolith particles: the smaller the size, the greater the

concentration and the smaller the

He/

He isotope ratio [30,

31]. The concentration also increases with increasing age of

exposure and the maturity regolith, i.e., it depends on the

ionizing irradiation dose. However, the greatest change in

the concentration of implanted helium is observed depend-

ing on the chemical and mineral composition of the regolith

particles and can vary in a very wide range, up to 3 orders of

magnitude and more [32]. The maximum content of

helium-3 is observed in ilmenite (FeTiO

), which is the main

ore mineral of titanium in mare lunar basalts. Selective

enrichment by solar wind ions of regolith depending on the

mineral composition leads to heterogeneous regional distri-

bution of helium isotope concentration and other noble gases

in lunar soil [33–35].

To estimate the concentration, distribution and predicted

helium-3 stocks in the lunar soil on the Near and Far sides of

the Moon, different models based on remote optical sensing

of distribution of chloroform elements TiO

and FeO with

correlation of helium-3 content in regolith, as well as the

degree of soil maturity and solar wind ﬂux density at dif-

ferent latitudes [35,36], and model regolith thickness

[34,37] were used. The purpose of this work is studying the

concentration and distribution of helium isotopes in the lunar

soil based on direct measurements of helium content in

different minerals, in the bulk composition of regolith in

areas of distribution of mare low-titanium and high-titanium

basalts and Highlands’s anorthosites, as well as estimating

predicted helium reserves in different geological complexes

with different bulk composition of regolith and underlying

rocks, different helium content and different regolith

thickness.

2 Helium Implantation and Trapping

in Minerals of the Lunar Regolith

Lunar soil consists of bedrock fragments and such particles

as glass, breccias, agglutinates, which were formed during

meteoritic bombardment. The main rock-forming minerals

are anorthite, bitovnite (basic plagioclase), olivine and

pyroxenes. The main ore mineral in mare basalt is ilmenite.

The regolith contains a signiﬁcant amount of glass, mainly

of impact origin. The regolith composition is mainly deﬁned

by underlying rocks composition, with the addition of

impact craters ejects from other areas, and meteoritic com-

ponent (*1 to 2 wt%). The regolith depletion in volatile

components due to impact melting and evaporative differ-

entiation is observed [38]. Constant inﬂuence of solar wind

and cosmic radiation enriches particles and minerals of

regolith with hydrogen, helium isotopes, rare gases, cos-

mogenic isotopes, and probably, promotes formation of

reduced forms Fe, Ti, Si and other elements in surface layers

of mineral particles. According to experimental data,

metallic iron Fe

may form without participation of reducing

agent (implanted hydrogen ions of solar wind), as well as

bypassing process of iron condensation from impact-formed

steam. Formation of chains of nanophase iron spherules in

glasses and on surfaces of particles and minerals can occur

thermo-reductive way during shock wave passage in shock

melt because of meteorite and micrometeorite bombardment

[39].

The general structure of the noble gas content in the lunar

soil quite corresponds to the predicted cosmic prevalence of

376 E. N. Slyuta and O. I. Turchinskaya

these gases. The observed saturated

He concentration on the

surface of ilmenite grains equal to 10

–3

He cm

−2

(3 10

atoms

He cm

−2

) corresponds to the integral solar

wind ﬂux of 7 10

atoms cm

−2

[30]. Such a dose of

irradiation corresponds to an exposure time of about

300 years at the present intensity of the solar wind ﬂux. At

such radiation levels, heavy saturation effects are expected,

which are likely to affect the relative content of captured

solar wind ions. For example, the maximum experimental

dose of saturation with protons on the quartz surface is

observed at 5 10

atom cm

−2

[40].

Lunar soil has a complex layered structure and its own

stratigraphic and geochemical history, which can be traced

back to the formation of underlying rocks (Fig. 1). An

average lunar soil formation rate is approximately 1.5 mm

per 1 Ma [41]. Layers are a stratiﬁed sequence of unstable

along strike deposits of ejections from the surrounding

impact craters, spaced from the ﬁrst meters to several hun-

dred kilometers, depending on size of these craters. There-

fore, a layer of more mature (older) regolith can partially

overlap a layer of immature young regolith. Hyperbolic

distribution of lunar soil density with depth and excessive

compaction and over compaction of regolith not deep from

the surface is explained by micrometeorite and ﬁne meteorite

bombardment, which loosens the surface layer and, on the

contrary, compacts underlying regolith layers [42]. Com-

plete mixing occurs only in the uppermost layer with a

thickness of about 1 mm, until a new ejection covers this

layer and removes it from the exposure zone by solar wind

and exogenous recycling. During this time, the 0.1 mm thick

layer will turn over more than 2000 times, the 1 mm thick

layer will turn over 250 times, and the 1 cm thick layer will

turn over once in 10

years [43].

Each layer can differ in bulk chemical and mineral

composition, particle size, regolith maturity, and exposure

age. At the same time in the layer itself there may be par-

ticles and minerals of lunar rocks not only of different

composition, but also age of formation. The solar wind

exposure age on the lunar soil determined by maturity index

is about 200 Ma [44]. Sometimes the lunar soil exposure age

exceeds this value twice and more. The soil exposure age

buried in 62 cm depth in the Taurus-Litre Valley (Apollo

17) is estimated to be 550 ±60 Ma [45]. Thus, the irradi-

ation dose of minerals and regolith particles by protons and

helium signiﬁcantly exceeds the saturation dose.

Depending on the mechanism of retention in lunar soil of

trapped noble gases from solar wind two main types of

helium are distinguished: weakly bound, saturating pore

space of lunar regolith, and implanted in particles and

minerals of lunar soil. Due to the high diffusion and evap-

oration rate of weakly bound helium, which reaches 10

[34], most of the helium escapes from the lunar regolith.

Nevertheless, the content of the remaining helium exceeds

the solubility of helium in the lunar regolith by 15–20 orders

of magnitude under the conditions of rareﬁed lunar atmo-

sphere [46], which indicates a certain ability of the lunar soil

to retain implanted volatile components.

The content of weakly bound helium in the lunar soil is

determined by diffusion, the rate of which is determined by

the temperature and different densities of the solar wind ﬂux

at different latitudes [34]. The accumulation of weakly

bound helium in the lunar regolith largely depends on the

surface temperature and does not depend on regolith com-

position. The content of this helium type substantially

increases at high lunar latitudes characterized by low diurnal

temperatures and the minimum amplitude of the diurnal

temperature variations. It is assumed that the content of

weakly bound isotope

He in the Polar Regions of the Moon

can reach 40–50 ppb [34,36]. This type of helium, as

compared to the implanted component, is characterized by a

more uniform distribution, the highest availability, and,

apparently, the highest concentration in the Polar Regions.

Weakly bound helium is easily released under thermal and

mechanical effect on the lunar soil and requires the devel-

opment of special methods for in situ research. The weakly

bound type of gases is one of the least studied in the lunar

regolith [47].

In contrast to weakly bound gases, implanted gases are

stable under mechanical and temperature effects on regolith

within several hundred degrees and can be sampled and

delivered to the Earth together with lunar soil without special

losses and studied in laboratory conditions. This property

makes this type of gas the most studied type. Direct mea-

surements of concentrations of noble gases trapped by

regolith particles from the solar wind composition were

performed for all regolith samples delivered by Soviet

automatic lunar stations and operated Apollo expeditions.

The study of

He concentration in size fractions of regolith

showed a clear dependence of concentration on the size of

fraction—the smaller the size of regolith particles, the

greater the concentration of helium-3. The observed distinct

inverse proportional correlation of gas content depending on

regolith grain size (Table 1) is approximated by the

expression

c1dn;

where cis a gas concentration, dis a particle size, and an

exponent nis estimated in the range from 0.58 to 0.65 for all

noble gases [30]. Lunar regolith consists of 50% of

particles < 50 µm in size [48], which contain up to 80%

of all trapped helium [49]. Thus 90% of the trapped helium

in lunar regolith is contained in fraction of size < 100 l[31].

For ilmenite grains also observed a clear dependence of

the content of trapped gases on the grain size. The exponent

Helium-3 in the Lunar Soil 377

Fig. 1 Schematic section of the structure of the loose layer of lunar

regolith with a borehole in the center. Parallel shading shows the

layered structure of the regolith. The underlying rocks are shown by

cross-hatching. Above is a photo panorama from the Apollo 17 landing

site (Credit NASA)

378 E. N. Slyuta and O. I. Turchinskaya

(n) for grains of ilmenite mineral (FeTiO

) ranges from 1.15

to 0.82. This dependence of a gas content on the grain size

can be explained by concentration of gases in the surface

layer of individual grains, i.e., the smaller the particle size,

the greater the particle surface relative to the soil density.

The dependence degree of gas content on grain size for

ilmenite is higher (Table 2) than for bulk regolith compo-

sition and is approximately constant per unit particle surface.

This means that saturation time of regolith with noble gases

does not depend on size of regolith particles and is deter-

mined only by the exposure time. Helium content in frac-

tions of approximately the same size of ilmenite in

comparison with a similar fraction of regolith, where ilme-

nite in its natural percentage is also present, is almost 4 times

higher (Tables 1and 2). Separate particles of regolith, for

example, glass spherules, which possess an amorphous

structure, in relation to bulk composition of regolith are

characterized by even greater intensity of diffusion losses of

helium and contain the smallest amount of trapped helium in

comparison with other rock-forming minerals [30].

Using the method of successive etching of the surface of

ilmenite particles, it was found that practically all trapped

helium and other noble gases are concentrated in the surface

layer 200 nm thick (Table 3). The content of the isotope

formed as a result of ﬁssion of radioactive element nuclei in

mineral particles of regolith was determined in heavily

etched samples of ilmenite grains, in which the surface layer

containing the implanted isotope

He was removed. The

amount of helium-3 formed by nuclear reactions was esti-

mated to be 0.7 ±0.2 ppb, which is generally in good

agreement with the regolith age estimated from xenon decay

[30]. Taking into account this value, the corrected ratio of

implanted

He/

He isotopes in ilmenite is within 2590–2840

and averages 2720 ±90. For regolith bulk composition for

different size fractions the isotopes ratio is not homogeneous.

For coarse fractions the measured isotope ratio

He/

exceeds 2500, and with correction this value increases about

10% and agrees with the value characteristic of ilmenite

[30]. The isotope ratio for thin regolith fraction is less than

2400. The isotope ratio correction for this fraction is less

than 2%. The difference can be explained either by the effect

of grain size or by a systematic difference in mineral com-

position of different fractions. The addition of the

He iso-

tope because of decay of U and Th over 4.5 billion years is

negligibly small compared to the implanted helium.

The implanted helium content is determined by compo-

sition and structure of minerals in lunar regolith and varies in

a very wide range up to three orders of magnitude or more.

Crystal lattice radiation-induced defects trap and retain

helium ions much efﬁciently than ones in the amorphous

structure retain [50]. The binding energy of a trapped helium

atom in vacancy traps of the crystal lattice is determined by

the occupied defect type and reaches more of 1 eV [51,52].

The theoretical calculations using the SRIM2010 pro-

gram [53] showed that the maximum ionization energy

losses of hydrogen ions (dE/dx) during interaction with

quartz should occur at 80–90 keV energy (Fig. 2)[54].

When hydrogen ions with energies less than 80 keV and

more than 90 keV are irradiated, the ionization losses in the

interaction of hydrogen ions with quartz decrease. This is

explained by the fact that at low velocities of ionizing

radiation particles, when vu, where uis the mean

velocity of electron in atom, the overcharge effect becomes

signiﬁcant, which consists in the fact that the passing particle

captures (and sometimes, on the contrary, loses) electrons

and becomes neutral [55]. Overcharging leads to a reduction

of ionization losses. At high energies, the effect of electric

polarization of the medium under the action of the particle

Table 1 Distribution of helium

isotopes by size fractions of

regolith from the Apollo 11

landing site [30]

# Fraction, µm Content

He, ppb Content

He, ppm

1 130 4.6 11.5

2 90 5.6 14.5

3 42 6.8 17.8

4 15 15.8 40.6

5 3.7 37.2 89.3

6 2.0 64.2 153.4

7 1.4 95.0 221.4

Table 2 Content of helium

isotopes in different fractions of

ilmenite from the Apollo 11

landing site [30]

# Fraction, µm Content

He, ppb Content

He, ppm

1 105 7.5 19.4

2 65 15.3 37.9

3 41 22.2 59.3

4 22 45.6 120.4

Helium-3 in the Lunar Soil 379

ﬁeld is effective. Polarization leads to sharp reduction or, as

they say, to screening of the particle's ﬁeld and, conse-

quently, to reduction of losses.

At low irradiation energies and doses at which hydrogen

ions saturation of quartz samples surface occurs, rapid

destruction of quartz crystal lattice and formation of amor-

phous ﬁlm on the crystal surface [54]. At energies close to

the maximum ionization loss energy of hydrogen ions in

quartz about 90 keV, as X-ray diffraction analysis shows,

inter-nodal defects develop to a depth of 1 µm, which lead to

the increase of the quartz lattice parameter Δd/d [54]. In this

case, the amorphous layer is not formed, but the micro-

crystalline structure of the disturbed layer is preserved.

Unlike quartz, in ilmenite at low irradiation energies, the

microcrystalline structure of the disturbed layer is preserved,

in which radiation defects of the crystal lattice continue to

develop [56], which increases the adsorption capacity and

reduces the degree of diffusion losses of trapped ions.

Amorphization of the crystal structure of ilmenite begins at

energies of about 120 keV [57], which is approximately an

order of magnitude higher than that of quartz and alumi-

nosilicates [58]. Unlike rock-forming minerals of dielectrics,

the main ore mineral of lunar basalts ilmenite is a semi-

conductor with a hole conductivity [59]. It is supposed, that

presence of conductivity at interaction with charged particles

of solar wind allows keeping crystal structure to a mineral.

As in radiation-induced amorphous ﬁlms of silicates and

aluminosilicates [60], the chemical composition of the dis-

turbed microcrystalline layer of ilmenite also changes. At the

boundary with the unchanged phase of the host mineral,

compared with its composition, iron depletion is observed,

while in the upper part of the disturbed layer, on the con-

trary, enrichment with reduced metallic iron [57]. Titanium

in the disturbed layer also changes its valence from Ti

and Ti

. When the ions destroy the bonds of the

ilmenite crystal lattice, a 2–threefold decrease in the O/Fe

and O/Ti ratios is also observed, indicating a signiﬁcant loss

of oxygen.

Under inﬂuence of ionizing irradiation in amorphized

layer of silicates, aluminosilicates and oxides, apparently,

radiation-induced fractionation of isotopes Fe and, probably,

isotopes Ti and other elements can occur. During irradiation

of quartz samples with energy of 20 and 110 keV by protons

with implanted

and

isotopes it has been founded,

that not only general shift of Fe isotope concentration in

depth on the quantity about 20 nm occurs, but at enough

high energy of hydrogen ions (65–200 keV) radiation-

induced fractionation of Fe isotopes is observed [61]. The

value of the radiation-induced fractionation of Fe isotopes

(5 nm) is approximately equal to the observed value of the

kinetic mass fractionation (5.8 nm), but with the opposite

sign.

The metallic Fe

content in the amorphous mineral layer

is determined by the signal intensity of ferromagnetic reso-

nance (I

)[62]. The ratio of the signal intensity I

to the total

FeO content in regolith by weight % characterizes the

regolith maturity degree. The parameter (TiO

I

/FeO) is

used to describe the total dependence of the

He content on

the ilmenite content and the regolith maturity (Fig. 3)

3He ppbðÞ¼0:2043 TiO2Is=FeOðÞ

0:645;

The formation of an amorphous layer on the mineral surface

as a result of ionizing irradiation, apparently, leads to

decrease in the efﬁciency of traps and, accordingly, to a

decrease in the helium content. Implantation depth of solar

wind ions is determined by the ion mass, their energy and

the target composition (Fig. 4). If hydrogen ions implanta-

tion with energy of 20 keV into quartz does not exceed

250 nm, the implantation depth of hydrogen ions with

Table 3 Distribution of implanted helium in the surface layers of ilmenite grain [30]

# Fraction, µm Layer thickness, µm Content

He, ppb Content

He, ppm

141 –27.0 69.4

2 41 0.16 19.9 52.7

3 41 0.19 10.8 26.4

4 41 0.35 3.3 6.7

Fig. 2 Ionization energy loss of hydrogen ions (dE/dx) related to

interaction with quartz as a function of irradiation energy calculated

using the SRIM2010 program [53]

380 E. N. Slyuta and O. I. Turchinskaya

energy of 90 keV increases three times and reaches 850 nm

[32]. The similar distribution of hydrogen on depth

depending on irradiation energy is observed in crystals of

silicon, and the value of average run of hydrogen ions with

energy about 100 keV also makes about 1 l[40].

Calculations with the program SUSPRE [63] show that

with the increase of energy from 1 to 3 keV the depth of

proton implantation in anorthite (Ca(Al

) increases

three times regardless of the ﬂux density, whereas the degree

and depth of amorphization much more depends on the ﬂux

density [58]. If at a ﬂux density of 1 10

atom cm

−2

, the

implantation depth outpaces the development and depth of

amorphization, then at a ﬂux density of about 1.6 10

atom cm

−2

the implantation is actually localized inside an

already well-developed amorphous layer (Fig. 5). The same

tendencies are observed in the case of irradiation by He

ions

with the only difference that the thickness of the amorphous

layer at high ﬂux density coincides with the maximum depth

of He

implantation. At the same time the implantation

depth and thickness of the amorphous layer at helium irra-

diation is approximately two times greater than at proton

irradiation (Fig. 6).

At increase of energy from 1 to 3 keV the depth of proton

implantation in quartz (SiO

) as well as in anorthite increases

almost three times regardless of ﬂux density. The extent and

depth of amorphization of quartz surface under the action of

ionizing irradiation depends mainly not on energy, but on

ﬂux density. At ﬂux densities of 1 10

atom cm

−2

and

less, the implantation depth greatly exceeds the development

and depth of amorphization, regardless of the proton energy.

At doses, exceeding 1 10

atom cm

−2

the implantation is

actually localized inside the forming amorphous layer

Fig. 3 Content of He depending on the parameter (TiO

I

/FeO)

[28]

Fig. 4 Dependence of the implantation depth of protons and He

ions

in quartz and anorthite on the ions’energy [32]: 1—implantation of

protons in quartz; 2—implantation of protons in anorthite; 3—

implantation of He nuclei in quartz; 4—implantation of He nuclei in

anorthite

Fig. 5 Protons’implantation depth and amorphization degree (disor-

der) in anorthite depending on protons’energy and a dose for 1 keV

D = 0.96 10

atom cm

−2

, for 2 keV D = 1.3 10

atom cm

−2

for 3 keV D = 1.6 10

atom cm

−2

:adistribution of the implanted

protons’concentration; bamorphization degree (disorder) of an

anorthite lattice

Helium-3 in the Lunar Soil 381

regardless of the proton energy (Fig. 7). The complete

(100%) amorphization of quartz surface is developed at the

doses exceeding 8 10

atom cm

−2

, and at ﬂux density of

1.6 10

atom cm

−2

, the thickness of amorphous layer on

the quartz surface achieves 100 nm (Fig. 7). When irradiated

with He

ions, the depth of quartz structure destruction and

amorphization, regardless of energy and dose, always coin-

cides with the maximum ion implantation depth (Fig. 8).

Intensity of amorphization is also mainly deﬁned by a dose

of irradiation (Fig. 8).

Thus, at dose increase up to integral value of ﬂux

(7 10

atom cm

−2

) observed in lunar regolith, all

chemical and physical processes of space (geochemical)

weathering of anorthite and quartz particles in lunar regolith,

apparently, will occur inside the formed radiation-induced

amorphous ﬁlm on crystal surface, not reaching the crystal

structure of mineral. In contrast to protons, the maximum

concentration of He

ions regardless of dose in both anor-

thite and quartz will accumulate in the transition zone

between the amorphous and crystalline phases of the

mineral.

The lowest content of noble gases in impact and volcanic

glasses is observed. Helium-3 in green glass spheres in lunar

soil samples of Apollo-15 is in the range of 0.02–0.3 ppb

(average for all size fractions about 0.2 ppb), and Helium-4

in the range 7–605 ppb (average for all size fractions 100–

200 ppb) [64–66]. It is about 100 times less, than in the bulk

regolith composition.

Similar small helium content in basic plagioclase are

observed, where

He content varies in the range 0.02 to

0.2 ppb, and

He from 33 to 500 ppb [66,67]. As noted

above, for all crystalline minerals of lunar regolith, including

plagioclase, there is an inverse proportional dependence of

helium concentration on particle size—the smaller the size,

the higher the concentration [30,66,68]. In contrast, a direct

proportional dependence, although not as pronounced, is

observed for green glasses: the smaller the particle size, the

smaller the helium concentration [64,66]. Probably, this

dependence is explained by the inclusions of maﬁc minerals

in larger glasses. Helium content in magnetic glasses with

Fig. 6 Implantation depth of He

and amorphization degree (disorder)

in anorthite depending on ions energy and a dose for 4 keV

D=210

atom cm

−2

, for 8 keV D = 2.8 10

atom cm

−2

, for

12 keV D = 3.5 10

atom cm

−2

:adistribution of the implanted

helium concentration; ban amorphization degree (disorder) of an

anorthite lattice

Fig. 7 Protons’implantation depth and amorphization degree (disor-

der) in quartz at constant energy of 3 keV and a doses D = 1 10

atom cm

−2

,D= 8 10

atom cm

−2

, and D = 1.6 10

atom cm

−2

adistribution of the implanted protons’concentration; ban amor-

phization degree (disorder) of a quartz lattice

382 E. N. Slyuta and O. I. Turchinskaya

large number of such inclusions signiﬁcantly increases

compared to green glasses [67].

The helium highest content in ilmenite are observed. In

grains of ilmenite sized 10–14 µm, the

He content can

reach 130 ppb, and

He—360 ppm [68]. Helium isotopes

content in bulk regolith composition of the same fraction in

lunar soil samples of Apollo 12 is 12 ppb of

He and

30 ppm of

He.

He content in bulk regolith composition

without separation into size fractions is almost two times less

and is 7.1 ppb and

He is 16.5 ppm.

The

He content in olivine with a grain size of 25–42 lm

is 2.9 ppb and

He is 6.24 ppm [65]. In the mixed fraction of

olivine and pyroxene grains with a grain size of 25–42 lm,

the helium isotope content is similar: 2.9 ppb and 6.2 ppm,

respectively [66]. However, the pure pyroxene fraction with

approximately similar grain size of 30–48 µm contains

implanted helium two times more (5.7 ppb

He and

13.4 ppm

He) than olivine [67].

Thus, helium content in glasses and plagioclases of the

lunar soil is approximately 100 times less than in bulk

regolith composition, but helium content in ilmenite, on the

contrary, is approximately 10–12 times more than in bulk

regolith composition of similar fraction and about 20 times

more in comparison with bulk regolith composition without

separation into fractions. Olivine and pyroxene are charac-

terized by the medium helium content compared to glass and

ilmenite. Obviously, under equal irradiation conditions, in

which the ilmenite grains were together with other minerals

of the regolith, the different helium content is due to the

different mineral composition and structure of the target, i.e.

due to the variety and number of defects-traps.

3 Helium Content in Regolith of Lunar Maria

and Highlands

Mare rocks are represented mainly by lava rocks of the basalt

type, which ﬁll the depressions of lunar mares. Pyroclastic

material is also found. In general, mare rocks compose about

1% of the lunar crust. The predominant mare rocks of the

Moon are mare basalts. In bulk chemical composition marine

basalts correspond to rocks of gabbro-basalts group and are

usually deﬁned as ilmenite, olivine, cristobalite basalts (gab-

bro), etc. [69,70]. The petrographic speciﬁcity of mare basalts

is in the smaller grain size (hundreds of microns) and in the

practical absence of volcanic glass. The major rock-forming

minerals are clinopyroxenes and plagioclase (An50-95),

sometimes olivine (Fo50-75); the major ore mineral is ilmenite

(FeTiO

). The ilmenite content varies from 0.1–1wt%in

low-titanium basalts [71,72]to10–20 wt% in high-titanium

basalts [73]. Formation of mare basalts which cover about

20% of the Moon's surface [74] is connected with the pro-

cesses of partial mantle melting, and the difference in mineral

composition of basalts, apparently, with different depth of

melt formation, and/or lateral changes in composition of lower

crustal layers and upper mantle [41,75].

Lunar pyroclastic material is a rare type of lunar marine

formations [76,77]. Pyroclastic material is represented by

green and orange glasses—mainly in the form of glass

globules and their fragments, which have no direct equiva-

lents in chemical composition among crystalline rocks.

Green glasses have a primitive maﬁc composition and are

considered to be the least differentiated lunar matter. The

particle surface of green and orange glasses is strongly

enriched with Zn, Pb, F and other volatile components,

which is associated with the processes of condensation of

volcanic (fumarolic) products. The glasses have an amor-

phous structure and are characterized by the lowest content

of noble gases trapped from the solar wind.

Ultrabasic rocks, which, as well as pyroclastic material,

are extremely rare, occur as xenoliths in mare basalts. The

rocks are represented by cataclased and recrystallized

dunites, and less frequently by peridotites. They consist

mainly of olivine (Fo9-12) with an admixture of pyroxenes,

Fig. 8 Implantation depth of He

and amorphization degree (disorder)

in quartz depending on dose of D = 1 10

atom cm

−2

D=110

atom cm

−2

and D = 3.33 10

atom cm

−2

at constant

energy of 12 keV: adistribution of concentration of the implanted

helium; ban amorphization degree (disorder) of a quartz lattice

Helium-3 in the Lunar Soil 383

plagioclase, metallic iron, and troilite. Formation of these

rocks is associated both with the early stage of global dif-

ferentiation of the Moon (age of mantle dunites is close to

the age of the Moon), and with later stages of formation of

the lunar crust [69,70].

Highlands’s rocks are represented by feldspathic rocks,

which are subdivided according to their chemical and min-

eralogical composition into two main groups: lunar anor-

thosite rocks and lunar non-maria basalts [69,70].

Structurally, these rocks are predominantly breccias with

blast and cataclase matrix, granulites, and cataclasites. They

are the oldest lunar rocks whose age—up to 4.5 billion years

—is close to the time of planetary body formation. Minimum

age of brecciation (metamorphism) is *3.9 billion years.

Formation and brecciation of Highland rocks occurred dur-

ing intense meteorite bombardment. Highlands’s rocks are

the main type of lunar crust rocks.

Among Highlands’s rocks the most widespread are rocks

of anorthosite-norite-troctolite (ANT) series, gabbro-norites

and gabbro-anorthosite. The latter are the main type of rocks

of the lunar Highlands. The rocks are characterized by high

content of Al (Al

> 24 wt%), Ca, Mg and some rare

elements. The main minerals are basic plagioclase (mainly

anorthite), olivine (Fo70-95), orthopyroxenes (enstatite and

bronzite), and clinopyroxenes (diopside, augite, pigeonite).

The content of ilmenite in the anorthosite rocks is usually

less than 0.1–0.2 wt% [78]. It is assumed that the rocks of

the ANT series are the product of gravitational differentia-

tion, i.e., plagioclase surfacing or precipitation of ferro-

magnesian minerals in the primary maﬁc melt [75].

Lunar non-mare basalts are a sparsely distributed group

of Highland rocks of the Moon with Al

content of 15–24

wt%. An important feature of non-mare basalts is the

increased content in some of them of the so-called

KREEP-component characterized by enrichment of K,

REE (rare-earth elements) and P (English abbreviation

K-REE-P), as well as Zr, Ba, U, Th and some other litho-

phile elements. According to this parameter, basalts with low

content of KREEP elements and KREEP-basalts are distin-

guished. In the American special literature, the “non-marine

basalt”is a medium-potassium Fra Mauro basalt. The pet-

rographic speciﬁcity of all non-mare basalts is that most of

them are breccias, which consist of clasts with a pronounced

magmatic structure with grain sizes up to hundreds of

microns. The formation of non-mare basalts is associated

with the processes of partial melting of lunar crust rocks at

relatively low pressures.

Acidic rocks of the Moon are the most exotic type of

lunar matter. Lunar acidic rocks occur as individual small

fragments in regoliths and breccias, and as cementing mas-

ses of breccias. The main minerals are pyroxene, tridymite,

cristobalite, and K-Ba-feldspar; secondary minerals are

medium plagioclase, apatite, vitlockite, and zircon. The

biggest and the most famous granite specimen is breccia

12013, delivered from the Apollo-12 landing site [79].

Formation of acidic rocks of the Moon is associated with the

process of residual melt liquation during fractional crystal-

lization of basaltic magma.

Regolith samples delivered from 9 different regions of the

Moon by Soviet lunar automated stations and American

Apollo manned expeditions have made it possible to mea-

sure the content in the bulk composition of regolith of dif-

ferent rocks—from low-titanium to high-titanium mare

basalts and in Highland anorthosite.

The observed dependence of the helium isotope content

on the size and composition of the regolith particles imposes

signiﬁcant restrictions on the use of measured values to

estimate predicted reserves of this isotope in the lunar soil.

First of all, it concerns representativeness of these estimates

to reﬂection of total particle size in regolith and total (bulk)

composition of regolith. The content estimates obtained for

discrete size fractions of the regolith as well as for separate

components of the regolith distinguished by mineral,

chemical, or other characteristics are unsuitable for use. In

contrast, the most objective and optimal estimates are those

obtained for representative samples of regolith with a full

range of particle sizes (< 1 mm) without partitioning into

fractions and components, i.e., for bulk samples. If data are

available for several bulk samples of regolith, the weighted

average value of

He content is found for the mass of the

investigated sample, which is taken as the basic value for the

speciﬁed landing area.

The average weighted contents of helium in bulk samples

of regolith with particle size fraction < 1 mm from the

Apollo 11 landing site can be obtained only for two values

(16.5 and 14.6 ppb) out of four, for which the mass of the

studied sample is indicated (Table 4). The weighted average

content of the isotope

He, equal to 15.1 ppb, and the iso-

tope

He, equal to 41.1 ppm, is taken as a value character-

izing the average isotope content in the regolith in the

Apollo 11 station area and in the Mare Tranquillitatis. The

weighted average value for the data in Table 1is 20.4 ppb,

but also cannot be used for reserves assessment because it

characterizes only a few discrete size fractions of the

regolith.

The

He content for a representative sample of regolith

from the Apollo 12 landing area in the Oceanus Procellarum

is 7.1 ppb and

He is 16.4 ppm [68]. The absence of data on

the mass of the investigated regolith samples from the

Apollo-14, and -15 landing sites does not allow us to obtain

an average weighted helium content for each of the landing

sites (Table 5), but the small scatter of values allows us to

use the average value [82]. An average value of

He equal to

5.7 ppb is taken for Apollo-14 station and 4.4 ppb for

Apollo-15 station. The average

He isotope content is taken

to be 15.1 ppm and 11.1 ppm, respectively.

384 E. N. Slyuta and O. I. Turchinskaya

Average concentration of

He and

He in regolith in the

landing area of manned expedition Apollo 16 (Table 6)is

1.4 ppb and 3.9 ppm accordingly.

The content of helium isotopes in bulk samples of rego-

lith at depth to 3 m according to the data of core drilling in

the area of Apollo 17 expedition landing in the southwest

part of the Mare Serenitatis (Table 7) is characterized by

relatively uniform distribution with small variations on

depth. This is also quite consistent with the relatively uni-

form distribution of the absolute age of the regolith expo-

sure, which averages over 62 cm depth to 550 ±60 Ma

[45]. The average content of

He and

He isotopes in this

area is 8.0 ppb and 20.8 ppm, respectively.

At the Soviet Luna-16 station in the eastern part of the

Mare Fecunditatis, sampling was carried out by means of

core drilling to a depth of 35 cm. Data on helium content are

known from several sources with different degrees of rep-

resentativeness of the samples depending on the fraction size

of the samples studied (Table 8). The most representative

sample of regolith studied is sample L16-19 [84], which is

the least enriched and most fully reﬂects the size range of

lunar regolith particles among the values presented in

Table 8. Thus, the content of

He equal to 7.9 ppb and

equal to 20.1 ppm is taken as the most representative.

Core drilling to a depth of 30 cm was carried out at the

landing site of the Luna-20 station in the Highland area. The

data obtained [88] were evaluated for the thin regolith

fraction with particle size less than 83 µm, the larger regolith

fraction was withdrawn (Table 9). The 2002-1 regolith

sample was taken from a depth of 5–10 cm from the lunar

Table 4 Content of helium

isotopes in regolith samples from

the Mare Tranquillitatis at the

Apollo 11 landing site

# Sample Mass, mg Content

He, ppb Content

He, ppm

He/

He References

1 10,084.40 3.507 16.5 44.0 2665 [80]

2 10,084.40 10.827 14.6 40.2 2750 [80]

3 10,084.18 –14.1 36.0 2550 [31]

4 10,084.59 –24.3 51.8 2130 [81]

Table 5 The content of helium

isotopes in the regolith at the

Apollo 14 and Apollo 15 landing

sites [82]

# Spacecraft Sample Content

He, ppb Content

He, ppm

1 Apollo 14 14,003 5.3 15.4

14,163 5.7 14.3

14,259 6.2 15.5

2 Apollo 15 15,601 4.6 11.0

15,091 4.2 11.2

Table 6 Content of helium

isotopes in the regolith in the

Highland region at the Apollo 16

landing site [83]

# Sample Content

He, ppb Content

He, ppm

1 63,321.7 1.6 4.5

2 63,341.4 1.5 4.2

3 63,501.22 1.4 3.9

4 67,941.15 1.0 3.0

Table 7 Content of helium

isotopes in regolith in the Apollo

17 landing site [45]

# Depth, cm Content

He, ppb Content

He, ppm Exposure soil age, Ma

10–5 11.2 27.7 360

2 26 3.4 8.9 330

3 62 7.0 19.1 560

4 93 6.6 16.8 610

5 133 7.1 18.2 490

6 173 8.2 21.6 530

7 213 9.6 26.1 610

8 253 8.5 22.6 550

9 290 9.8 26.0 490

Helium-3 in the Lunar Soil 385

surface and the 2004-1 sample from a depth of 15–20 cm

from the surface. The data obtained [89] were evaluated for

the size fraction of regolith < 400 µm. Taking into account

the dependence of the helium concentration on the size

fraction of regolith particles, this sample is less enriched and,

accordingly, more representative. Therefore, the

He content

equal to 3.1 ppb and

He content equal to 8.2 ppm are taken

as characteristic for the Highland area between the Mare

Fecunditatis and the Mare Crisium at the landing site of the

Luna-20 station.

The helium content for the offshore area in the southern

part of the Mare Crisium was obtained by studying the

regolith samples delivered by the Luna-24 station. Sampling

at the station-landing site was carried out using core drilling

to a depth of 225 cm. Helium content data were obtained for

regolith fractions of size 375 lm[89] and 250 lm

[90]. Table 10 shows the weighted average values for each

regolith sample for a particular depth interval, since the

regolith samples were divided into three or four size groups

during the study. The interval-weighted average

He content

at the landing site of Luna-24 station at a depth of 218 cm is

3.4 ppb and

He content is 7.2 ppm. It should be noted that

the data for station Luna-24 are the most optimal from the

point of view of estimation of

He reserves as they not only

reﬂect almost all basic size range of regolith particles

without exclusion, but also allow to estimate average

weighted content at a depth up to 218 cm. It should be noted

that the content of implanted helium isotopes in the regolith

of low-titanium basalts in the Mare Crisium gradually

decreases with depth [92].

In general, the average ratio of

He/

He isotopes in the

regolith of different bulk composition is about 2500. Based

on the analysis of the available data on the content of helium

in the lunar regolith in the landing areas of Soviet automatic

stations and American manned expeditions, the most repre-

sentative values have been determined, which are recom-

mended for use at estimation the predicted reserves of

helium in the lunar regolith of the corresponding composi-

tion (Table 11).

Thus, the loose regolith layer in the area of distribution of

high-titanium basalts is characterized by the highest con-

centration of implanted helium isotopes and, accordingly,

other noble gases. The concentration of implanted helium

isotopes in the bulk composition of regolith decreases with

Table 8 Content of helium

isotopes in the regolith at the

Luna-16 landing site

# Sample Fraction, µm Content

He, ppb Content

He, ppm References

1 L16-19 1–400 7.9 ±0.35 20.1 [84]

2 7-1a 83 12.4 33.1 [85]

3 G-7 125 14.3 33.6 [86]

4 G-49 40–150 4.2 14.1 [87]

Table 9 The content of helium

in the regolith at the Luna-20

landing site

# Sample Content

He, ppb Content

He, ppm References

1 L2010 3.1 8.2 [89]

2 2002–1 4.0 ±0.36 10.0 [88]

3 2004–1 5.89 ±0.45 15.0 [88]

Table 10 The content of helium

in the regolith at the Luna-24

landing site

# Sample Depth, cm Content

He, ppb Content

He, ppm References

1 24,077.9 77–85 4.9 12.1 [91]

2 24,092.4 92–95 4.4 10.9 [90]

3 24,109.13 109–121 3.3 7.4 [91]

4 24,118.4 118–121 4.3 10.4 [90]

5 24,143.4 143–146 4.1 10.5 [90]

6 24,149.15 149–163 3.1 5.9 [91]

7 24,174.10 174–183 3.1 7.3 [91]

8 24,182.15 182–196 2.2 4.3 [91]

9 24,184.4 184–187 2.3 5.7 [90]

10 24,210.9 210–218 2.6 6.0 [91]

386 E. N. Slyuta and O. I. Turchinskaya

decrease of ilmenite content in basalts from high-titanium to

low-titanium. The minimum concentration of helium is

observed in Highlands’s anorthosite rocks characterized by

the minimum content of ilmenite and a lower content of

maﬁc rock-forming minerals olivine and pyroxenes.

4 Lunar Soil Thickness

One of the ﬁrst estimates of the thickness of the loose

regolith layer according to data from automatic stations was

made at the landing site of Luna-9 station in the South-

eastern part of the Oceanus Procellarum. Based on the

analysis of the depths of the largest craters (about 1 m)

observed on the panoramic images, it was concluded that the

thickness of the regolith at the landing site exceeded 0.2 m

[93]. Attempts to directly measure the thickness of the

regolith were made in the process of sampling the regolith

by means of core drilling and core tubing at the landing sites

of the Luna-16, Luna-20, Luna-24, and Apollo manned

expeditions. The maximum drilling depth (225 cm) by the

automatic drill rig LB-9 was achieved at the landing site of

Luna-24 in the Mare Crisium [94], and the maximum dril-

ling depth (305 cm) by the hand-held perforator was

achieved at the Apollo-17 landing site in the Mare Sereni-

tatis [95]. At the Apollo-15, and -16 stations, core drilling

was performed to a depth of 236 cm and 224.3 cm,

respectively [95]. Regolith sampling with core pipes was

carried out to a depth of 70 cm at all Apollo stations [96]. In

none of the 9 sites of direct sampling of the regolith at the

landing sites, the base of the loose regolith layer was

reached.

The thickness of the regolith was also evaluated by the

size of the craters, which had uncovered the underlying

rocks at the base of the regolith. The evidence of opening of

the underlying rocks was the presence of a placer of rocks on

the rim and in the area of the ejection of such a crater. This

method of estimation was used in the analysis of the regolith

thickness according to Lunokhod-1 and Lunokhod-2 data. In

the western part of the Mare Imbrium, in the Lunokhod-1

study area, the regolith thickness was estimated to be within

1–5m [97]. Regolith thickness in the eastern part of the

Mare Serenitatis in the Lemonier Crater (Lunokhod-2) was

estimated within of 2–3m[98].

Studies of the granulometric composition of lunar rego-

lith have shown a close relationship between the parameters

of particle size distributions, regolith thickness and regolith

maturity indices, which characterize the degree of processing

of lunar regolith [99]. The standard deviation of particle

sizes has the highest correlation dependence among the

parameters of particle size distributions with regolith thick-

ness. The found dependence is deﬁned by expression

rcm ¼1:53 þ0:102h;

where his the regional regolith thickness. The regolith

thickness estimates thus obtained at the landing sites of

Luna-16 (Eastern part of the Mare Fecunditatis) and Luna-20

(Highland area to North of the Mare Fecunditatis) were 5.3

and 11.6 m, respectively [99].

The statistical analysis of impact crater morphology and

crater population characteristics has also been successfully

applied to estimate the regolith thickness [100]. The former

is based on the dependence of crater shape on the regolith

thickness, the latter on the determination of the characteristic

crater size from which the deviation of the equilibrium crater

distribution is observed. The size of these craters at the

boundary of the equilibrium and non-equilibrium crater

populations is directly proportional to the age of the surface

and, correspondingly, the regolith thickness. Regolith

Table 11 The average content of

helium isotopes in the regolith at

the landing sites of the Soviet

automatic stations and the

American Apollo expeditions

# Spacecraft Landing site Regolith composition Content

He,

ppb

Content

He,

ppm

1 Apollo 11 Mare

Tranquillitatis

High-titanium basalts 15.1 41.1

2 Apollo 12 Oceanus

Procellarum

Basalts with medium ilmenite

content

7.1 16.4

3 Apollo 14 Fra Mauro Low-titanium basalts 5.7 15.1

4 Apollo 15 Mare Imbrium Low-titanium basalts 4.4 11.1

5 Apollo 16 Highland Highland anorthosites 1.4 3.9

6 Apollo 17 Mare Serenitatis Basalts with medium ilmenite

content

8.0 20.8

7 Luna 16 Mare

Fecunditatis

Basalts with medium ilmenite

content

7.9 20.1

8 Luna 20 Highland Highland anorthosites 3.1 8.2

9 Luna 24 Mare Crisium Low-titanium basalts 3.2 7.2

Helium-3 in the Lunar Soil 387

thickness data were obtained for 12 sites ranging from 336 to

3179 km

[100]. According to these estimates, the lowest

thickness (3.3 m) is observed in the Southern part of the

Oceanus Procellarum in the area of the Flamsteed crater

(landing area of the Servier 1 spacecraft). Moderate regolith

thickness (4.6 m) is observed in western and southern parts

of the Mare Tranquillitatis (Landing Region of Apollo 11),

in the southern part of the Sinus Medii (Landing Region of

SC Servier 6), in the northern part of the Mare Cognitum

(Landing Region of SC Servier 3 and manned expedition

Apollo 12), and in the central part of the Oceanus Procel-

larum (Landing Region of SC Luna-13). The increased for

mare areas regolith thickness (7.5 m) is observed in the

northern part of the Sinus Medii and in the central part of the

Mare Imbrium. The regolith thickness at the Hipparchus

crater bottom in the Highland area reaches 16 m [100].

The regolith thickness at the landing sites of the Apollo

manned expeditions was also determined by instrumental

methods using electrical and seismic surveys. As a result of

seismic experiments it was found that the lunar regolith layer

is characterized by very low velocities of elastic longitudinal

waves (80–120 m s

−1

). The landing areas of the Apollo 11, -

12 and -15 expeditions are distinguished by relatively young

surface age and moderate thickness of the regolith. The

regolith thickness in the south-western part of the Mare

Tranquillitatis in the area of the spacecraft Apollo 11 landing

according to the data of seismic experiment is estimated at

4.4 m, in the northern part of the Mare Cognitum in the

landing area of the spacecrafts Servier 3 and Apollo 12 it is

estimated at 3.7 m, and in the foothills of the Montes

Apenninus in the Hadley Rille area in the Apollo 15 landing

area it is estimated at 4.4 m [101]. The thickness of the

low-velocity layer of lunar regolith (104 m s

−1

) in the Fra

Mauro area in the area of the Apollo 14 landing, according

to instrumental data, was 8.5 m, and in the Highland area in

the area of the Apollo 16 landing, 12.2 m [102]. The regolith

thickness within the mare area in the area of the Apollo 17

station landing (intermountain plain Taurus-Littrow to the

east of the Mare Serenitatis) according to less detailed

regional seismic model is estimated in the range of 7–12 m

[102]. The regolith thickness in the area of Apollo 17 station

according to the assessment [103], also made on the basis of

seismic experiment, does not exceed 8.5 m. A step change

of the dielectric constant typical of the transition from loose

regolith to denser underlying rocks according to electrical

prospecting data in the same area was observed at a depth of

7±1.0 m [104].

A model map of the regolith thickness distribution for the

Moon Near Side based on the correlation of the depolarized

and polarized components of the radio response at a wave-

length of 70 cm with the optical albedo (0.65 lm) and the

color index (0.65/0.42 lm) with a resolution of about 3 km

in the center of the hemisphere was obtained [105], which is

in satisfactory agreement with data obtained by other

methods (Table 12). The highest thicknesses of regolith

(more than 13 m) in Highland areas are observed in the

southeastern part of the Moon Near Side in the Highland

region. In the southwest part of the Near Side in Highland

region are observed moderate thicknesses of regolith—7to

11 m. This area represents the framing of the Mare Orientale

and corresponds to the age of formation of the Mare Ori-

entale basin. The northeastern part of the Moon Near Side is

represented by the Highland region with regolith thickness

from 9 to 13 m.

The model distribution of regolith thickness has a

bimodal character with maximums of about 5 and 10 m,

which corresponds to the average values of regolith thick-

ness for mare and Highlands [105]. The regolith thickness in

mare areas varies from 3 to 11 m. A small regolith thickness

(about 3 m) in some small areas of the Mare Serenitatis and

the Mare Nubium is observed. The maximum regolith

thickness in mare areas (9–10 m) in the areas adjacent to

some large craters (e.g., Aristillus Crater) is observed.

Among the mares, the Mare Humorum is characterized by an

average minimum regolith thickness of about 4.0 m, and the

Mare Nectaris is characterized by the deepest, about 9.6 m

(Table 13).

The dispersion of regolith thickness at Highland areas is

much wider—from 1 m in the highlands to 18 m and more

in the plateau areas with the age of underlying rocks of the

Donectarian system (>3.92 billion years). The minimum

values at the bottoms of impact craters (craters Tycho,

Theophilus, Langren, Copernicus, etc.) and near Schickard

Crater are observed. The highest thickness of regolith (more

than 13 m) in the southeastern part of the Moon Near Side at

Highland areas formed at the Donectarian period (>3.92

billion years) [108] is observed. The Donectarian age

Highland rocks are distributed at the southern, southeastern,

and central part of the Moon Far Side and occupy about half

of the hemisphere. Moderate regolith thicknesses of 7–11 m

at the southwestern part of the Near Side in the Highland

region [107] are observed. This area represents the framing

of the Mare Orientale and corresponds to the age of the

formation of the Mare Orientale basin in the early Imbrian

epoch. Approximately equal in area part of this framing is

traced on the Far Side of the Moon. The northeastern part of

the Near hemisphere of the Moon is represented by Highland

of the Nectarian period with a regolith thickness from 9 to

13 m. Highlands of the Nectarian age at the Far Side

occupies about one third of the area in the northeastern and

western parts of the hemisphere.

There is a direct dependence of the regolith thickness on

the surface age, which is explained by the time of exposure

of the rocks’surface from the moment of their formation -

the greater the surface age, the greater the regolith thickness.

This dependence agrees rather well with the

388 E. N. Slyuta and O. I. Turchinskaya

Table 12 The regolith thickness

at the landing sites of unmanned

spacecrafts and Apollo

expeditions

Spacecraft Regolith thickness [105], m Regolith thickness, m References

Luna-9 4.8 > 0.2 [93]

Luna-13 3.6 4.6 [100]

Luna-16 4.0 4.0 [106]

5.3 [99]

Luna-17 5.1 1.0–5.0 [97]

4.0 [106]

Luna-20 9.2 0.4 [106]

11.6 [99]

Luna-21 3.9 2.0 [106]

2.0–3.0 [98]

Luna-24 3.0 > 2.0 [94]

Surveyor 1 3.5 3.3 [100]

Surveyor 3 5,3 4.6 [100]

Surveyor 5 4.6 –

Surveyor 6 –4.6 [100]

Apollo 11 4.7 4.6 [100]

4.4 [101]

Apollo 12 5.3 4.6 [100]

3.7 [101]

Apollo 14 8.1 8.5 [102]

Apollo 15 6.0 4.4 [101]

Apollo 16 10.1 12.2 [102]

Apollo 17 7.0 7–12 [102]

8.5 [103]

7.0 ±1.0 [104]

Table 13 Average regolith

thickness in lunar Maria [107]Mare Regolith thickness,

Standard deviation (r

), m

Mare Serenitatis 4.1 0.8

Mare Tranquillitatis 4.1 1.1

Mare Crisium 4.6 1.6

Mare Fecunditatis 5.9 1.4

Mare Frigoris 7.4 2.1

Mare Imbrium 6.2 2.0

Mare Humorum 4.0 0.9

Mare Nectaris 9.6 2.3

Mare Vaporum 5.4 1.1

Mare Nubium 5.7 1.7

Mare Cognitum 4.9 0.7

Sinus Roris 7.5 1.9

Sinus Iridium 4.6 0.6

Sinus Aestuum 6.3 1.4

Oceanus Procellarum 4.8 1.6

Helium-3 in the Lunar Soil 389

chronostratigraphic subdivisions of lunar formations [101,

109], i.e. with the age of rocks of mare and Highland

regions. Thus, based on the geological map [108] it is pos-

sible to extrapolate these data for the Far Side of the Moon,

which can also be used to estimate the predicted helium

reserves on the Moon.

5 Predicted Reserves of Helium in the Lunar

Soil

Selective enrichment by cosmogenic isotopes of regolith

depending on its mineral composition, which is determined

mainly by underlying rocks, leads to non-uniform regional

distribution of concentration of helium isotopes and other

implanted gases in lunar soil. The highest concentration of

helium isotopes, as shown above, is observed in

high-titanium mare basalts, in which the content of the main

ore mineral ilmenite reaches 20 wt%. The areas of spreading

of high contents of TiO

oxides (5–10%) according to the

spectral remote sensing data actually reﬂect the content of

ilmenite in regolith and, correspondingly, the distribution of

high-titanium mare basalts. The spectral survey method is

based on correlation of the content of the main chromophore

elements Fe and Ti for albedo with albedo and color indices

in the visible and near-IR spectral ranges [110–112]. The

percentage content of TiO

according to spectral survey data

varies in the range from 0.01 in Highland areas to 10% and

Category

deposits

Near side Far side Total, t

He, t

He, т

He, t

He, т

I 90,695 246,859,399 –– 90,695 246,859,399

II 120,717 313,865,411 711 1,849,836 121,428 315,715,247

III 59,491 150,080,056 371 935,959 59,862 151,016,015

IV 138,777 367,088,777 5275 13,953,986 144,052 381,042,763

V 356,719 993,717,291 534,152 1,487,994,198 890,871 2,481,711,489

Total, t 766,399 2,071,610,934 540,509 1,504,733,979 1,306,908 3,576,344,913

392 E. N. Slyuta and O. I. Turchinskaya

6 Summary

Depending on the mechanism of trapping and accumulation

of trapped noble gases in lunar regolith, weakly bound

helium, which saturates the pore space of lunar regolith, and

helium implanted into particles and minerals of lunar rego-

lith are released from solar wind. The accumulation of

weakly bound helium in the lunar regolith largely depends

on surface temperature and solar wind ﬂux density

depending on geographic longitude and latitude, and prac-

tically does not depend on regolith composition. The content

of this type of helium increases essentially at high lunar

latitudes characterized by low diurnal temperature and

minimal amplitude of diurnal temperature variations; it is

extremely unstable and is easily released during temperature

and mechanical inﬂuences on the lunar soil, and requires

development of special methods of in situ investigation

[115]. It is assumed that the reserves of weakly bound

helium in the polar regions of the Moon may signiﬁcantly

exceed the reserves of implanted helium.

Capture and accumulation of implanted helium in the

lunar soil depends on chemical and mineral composition of

regolith particles, on age of exposure and regolith maturity

degree, on particle sizes, and can vary in a very wide range

up to few orders of magnitude. The helium and noble gases

lowest content are characteristic of glasses of impact and

volcanic origin and the main rock-forming mineral of lunar

Highland rocks—anorthite. The highest concentration of

implanted helium is characteristic for the main ore mineral of

mare basalts—ilmenite. Amorphization of the crystalline

structure of ilmenite under solar wind irradiation begins at

energies of ions an order of magnitude higher than those of

silicates and aluminosilicates, and crystal lattice

radiation-induced defects trap and retain helium ions much

stronger than amorphous structure retain. As the content of

ilmenite in basalts decreases from high-titanium to

low-titanium, the concentration of implanted helium isotopes

in the bulk composition of regolith decreases correspond-

ingly. Minimal concentration of helium is observed in

Highland anorthosite rocks characterized by minimal content

of ilmenite and lower content of maﬁc rock-forming min-

erals olivine and pyroxenes with average helium content as

compared to basalts. Selective enrichment of regolith with

solar helium depending on its mineral composition, which is

determined mainly by underlying rocks, leads to

non-uniform regional distribution of helium isotope con-

centration and other implanted gases in lunar regolith. The

highest concentration of helium isotopes is observed in

high-titanium mare basalts, in which the content of the main

ore mineral ilmenite reaches 20 wt%.

Depending on mineral composition of regolith and con-

centration of implanted isotopes ﬁve categories of deposits

are distinguished. The ﬁrst three categories cover areas of

distribution of high-titanium and low-titanium basalts and

are located in the territory of lunar mares in the Moon

equatorial region. Deposits with maximum content belong to

the richest and highest I category. Most reserves of

implanted helium in this category are concentrated in the two

largest ﬁelds located in the Mare Tranquillitatis and in the

Oceanus Procellarum. The predicted reserves of helium in

Category II deposits occupy an area twice as large, are

distributed much more evenly and are located in almost all

mare regions of the Moon. Approximately the same distri-

bution is typical for the deposits of the third category. The

fourth category of deposits unites low-titanium mare basalts

and adjacent complexes of Highland rocks in the coastal

zone where the mutual enrichment of Highland and mare

components occurs due to horizontal transfer of emissions

from impact craters with formation of extensive coastal

mixing zones. The ﬁfth category, the poorest by helium

content in lunar soil but the largest by reserves unites all

lunar Highlands that occupy more than 80% of lunar surface.

In general, in the loose regolith layer on the Moon, the

total predicted reserves of helium-3 are estimated as

1.3 10

tons, and helium-4 as 3.5 10

tons, that are

characterized by an extremely inhomogeneous distribution.

The reserves of implanted helium isotopes in the richest

deposits of categories I and II, which are of the greatest

practical interest, are concentrated on a relatively small area

and are estimated at about 2.1 10

tons of

He and about

5.6 10

tons of

He.

Acknowledgements The article is dedicated to the memory of Aca-

demician E. M. Galimov, a scientist and teacher, who initiated these

studies at the Vernadsky Institute. Chapter 5.“Predicted reserves of

helium in the lunar soil”was supported by a grant fromthe Russian Science

Foundation No. 21-17-00120, https://rscf.ru/project/21-17-00120/.

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396 E. N. Slyuta and O. I. Turchinskaya

基于溅射过程与降温历史的玄武质月壤来源反演

Article

Full-text available

Apr 2025

月表覆盖着一层结构松散的月壤, 是遥感和卫星观测及探月工程的重要研究对象. 成熟的月壤经历了复杂的撞击、溅射和翻耕过程, 其现今位置相比原岩发生了一定程度的转移. 确定月壤相对原岩的转移距离对相关研究具有重要意义, 这通常基于遥感数据及撞击模型分析展开. 基于玄武质岩浆喷发至月表后的冷却历史模拟, 本文证明月表熔岩流冷却历史主要受岩浆在熔岩流内部所处深度控制, 相似深度岩浆的冷却过程与熔岩流厚度关系较弱. 因此, 矿物扩散所记录的热历史不是熔岩流喷发强度/厚度的准确指标. 将熔岩流冷却历史与撞击溅射过程结合, 我们提出了基于扩散年代学恢复玄武质月壤来源(原地或异地)的新方法. Lunar soil, or regolith, which blankets the Moon’s surface, contains vital information about the Moon’s formation, geological history, and surface evolution. Understanding the origin and evolution of this material is essential for interpreting data collected during past and future lunar missions. One of the key challenges in lunar geology is tracing the provenance of lunar soil — that is, determining where it originally came from. This is especially critical because lunar soil is often transported and reworked over time, meaning its current location may not reflect its source. Mature lunar soil generally undergoes two distinct processes. The first is initial formation, which occurs through high-energy impact events that physically break down bedrock, generating fragments and ejecting them across the surface. The second is the gardening process, where micrometeorite bombardment and continual impacts churn and mix the upper regolith layers. This prolonged mixing leads to a homogenized material in terms of its original depth within the lava flow. Previous efforts to trace the origin of lunar soil have mainly relied on remote sensing data and theoretical impact ejecta models, which estimate the contribution of material from known craters or distant sources. Here we propose a novel method that combines impact modeling with thermal diffusion chronometry to link soil samples to depths within their source rocks as mare basalts. Using the Maxwell Z-model, which describes the excavation flow field of a crater-forming impact, we simulate the depth distribution of ejecta from a basaltic lava flow. This model allows us to predict how deep within a lava flow the material originated, based on the distance it was ejected from the impact site. Additionally, we simulate the cooling history of lunar lava flows. As a lava flow cools, minerals located at different depths within the flow experience different thermal histories, which are recorded in their diffusion profiles. These profiles can be measured using diffusion chronometry, providing a time-temperature record for individual mineral grains. Our findings show that the depth at which a mineral formed in the original lava flow is the primary control on its thermal history, rather than the overall thickness of the flow or eruption rate. While this demonstrates that diffusion chronometry provides a minimum estimate on the flux and/or volume of basaltic lava flow, it also enables us to estimate the original depth of soil grains with the lava flow. This integrated approach offers a new method for tracing the provenance of lunar soil using diffusion chronometry. It enhances our ability to interpret lunar samples in a geological context and provides useful information for future lunar missions.

The Influence of Lunar Environment Exposure on Characteristics of Nuclear Energy He-Xe Closed Brayton Cycle

Article

Jul 2024
ACTA ASTRONAUT

Unlocking the future of space resource management through satellite remote sensing and AI integration

Article

Apr 2024
RESOUR POLICY

This scientific study investigates how artificial intelligence (AI) and satellite remote sensing could work together to transform space resource management. As human activity in space continues to expand, the effective and sustainable utilization of celestial resources is of paramount importance. It begins by highlighting the evolution of space exploration and the growing interest in resource extraction beyond Earth's boundaries. It emphasizes the critical role of resource management for the success of future space missions. Advances in technology in recent times, including the implementation of in-situ resource utilization (ISRU) and self-governing mining systems, have significantly enhanced the possibility of extracting resources from celestial entities. While the economic feasibility of space mining is compelling, environmental concerns, sustainability, and intricate governance challenges necessitate careful examination. An approach for comprehending the complex field of space resource management is presented in this research. It delineates a clear roadmap of its content, offering a succinct summary of key objectives and sections, facilitating reader comprehension. The methodology includes a literature review of relevant research materials from Web of Science, Scopus, and Google Scholar sources. It investigates celestial bodies' resource potential, main challenges, and environmental implications. Preliminary contributions include one analysis of the potential applications of satellite remote sensing and AI technologies in mitigating these challenges, highlighting their pivotal roles in resource identification and management, proposing terrestrial solutions applicable to space resource management. The integration of AI into space resource management is discussed, emphasizing its potential to enhance safety protocols, resource allocation, and overall efficiency. Furthermore, it discusses international agreements and treaties governing space exploration and resource utilization while advocating for cooperation among space-faring nations and stakeholders. It concludes discussing the implications, benefits, challenges, areas requiring further attention, and future directions of integrating these technologies in space resource management.

Early steps toward the lunar base deployment: Some prospects

Article

Full-text available

Jan 2021
ACTA ASTRONAUT

The paper deals with key problems related to the initial stage of the Moon exploration in the coming decades. Moon exploration plans are on the agenda of the world's leading powers. Some important issues linked to of the Lunar Base development and the pre-construction studies on the selection of the most suitable regions for the purpose and along with their natural properties are discussed. We consider a scenario in which robots are widely used for further study and exploration of the Moon. The plan includes developing a global geological and geophysical reference network on the lunar surface and use mobile equipment equipped with drilling rigs. Such means (lunar rovers of a new generation) are in demand for the preliminary selection of the most suitable places for the Lunar Base construction as an initial element of the complex lunar infrastructure. Two types of lunar rovers are considered in detail: the prospecting and exploration lunokhod of the middle class “Geologist-Explorer” and the heavy lunokhod “Robot-Geologist”. They are intended to carry out regional geological, geochemical and geophysical surveying, sampling, analysis and comparison of data on the natural conditions of selected areas on promising routes with a radius of up to 500 km on the Near and Far side of the Moon. An important goal is data collection on the availability of such important local resources as water ice, frozen volatile and ore deposits. The issues of safety of humans stay in harsh conditions on the lunar surface and the possibility of protection from external factors are discussed, which plays an important role in the implementation of plans for the future lunar exploration.

Evidence for a Stratified Upper Mantle Preserved Within the South Pole‐Aitken Basin

Article

Full-text available

Jan 2021

The evolution and compositional structure of the lunar mantle has been extensively modeled but insufficiently constrained by observations. Here, we identify and characterize mantle materials exposed by the Moon's largest impact basin to better understand the composition, stratigraphy, and evolution of the upper mantle. The vast South Pole‐Aitken Basin (SPA) exhibits a broad, crescent‐shaped thorium and potassium distribution. These incompatible elements are predicted to be concentrated in the dregs of the lunar magma ocean during end‐stage crystallization. Through consideration of basin formation models convolved with subsequent geologic evolution, we demonstrate that the distribution and implied stratigraphy of Th‐ and K‐bearing materials across SPA are consistent with an upper mantle ejecta origin. The most pristine exposures of these materials are confined to northwest SPA and also exhibit elevated Ti and Fe (relative to the farside highlands) in association with a gabbronoritic mineralogy. This is consistent with late‐stage magma ocean assemblages predicted by petrologic models. In contrast, SPA impact melt derived from greater depths is associated with a low‐Ca pyroxene‐dominated assemblage. Together, these compositional patterns are evidence for a stratified ancient upper mantle. Importantly, the incompatible‐element‐enriched, ilmenite‐bearing ferroan gabbronoritic cumulates evidently had not participated in gravitational overturn at the time of SPA formation. Contrary to recent hypotheses invoking nearside sequestration of incompatible elements to explain hemispherical differences in crustal building and volcanic resurfacing, it follows that incompatible elements were globally distributed in the magma ocean at the time of SPA formation.

Experimental Model of the Formation of Nanophase Metallic Iron in the Lunar Regolith

Article

Full-text available

Jun 2020

One of the signs of “space weathering” on the Moon, including the effect of the solar wind and micrometeorite bombardment, is the formation of nanophase metallic iron (np-Fe0) in the lunar regolith, which is observed in condensate films on the surface of regolith mineral grains and in agglutinate glasses. The results of pulsed laser experiments simulating a micrometeorite “impact” on a basalt target are reported. Iron nanoglobules structured into chains and most likely marking the front of the shock wave were discovered in its melt products. The experiments clearly showed that np-Fe0 may be formed without participation of a reducing agent, such as implanted hydrogen ions of the solar wind, as well as bypassing the process of iron condensation from shock-generated vapor. The similar np-Fe0 chain structures were detected in the impact glass of the lunar regolith.

Experimental Modeling of a Micrometeorite Impact on the Moon

Article

Full-text available

Feb 2020

The shock-explosive processing of rocks by micrometeorite and meteorite bombardment on the sur-face of the Moon and other airless bodies of the solar system is a dominant geological and geochemical process that produces the loose layer of regolith. The paper presents results of modeling the process of a micrometeorite impact using a millisecond laser. The targets in the experiment were a sample of basalt of composition similar to those of basalts at Moon’s mare areas and a sample of basalt glass obtained by melting this basalt. At the laser “impact”, products ejected from the crater (glass spherules, droplets of various shapes, and condensates) and melting products in the crater were studied by electron microscopy, electron microprobe analysis with energy-dispersive spectrometers, X-ray diffraction, and X-ray fluorescence analysis. It has been shown that the glasses (melt drops) obtained in the experiment with the basalt target are characterized by a heterogeneous distribution of chemical composition. They were mixed in variable proportions as a result of melting the original minerals of the basalt. The spherules that have undergone significant evaporation differentiation in the experiment with a basalt target (crystalline basalt) make up about 25%. When the target was basalt glass, the proportion of the spherules (that have undergone profound evaporative differentiation) was ~90%. The glass was depleted in high-and medium-volatility components (Na2O, K2O, FeO, etc.). The most strongly differentiated glasses corresponded to high-alumina HASP glasses found on the Moon (Al2O3>34 wt%, SiO2<32 wt%)

Basic types of Moon’s resources and their mining and processing

Article

Full-text available

Apr 2017

E. N. Slyuta

The aim of the article is to give a brief review of the major problems connected with the determination of basic types of Moon's resources, conditions of their occurrence and spread in the regolith of the Moon and appraisal of possible reserves. It is shown that the most promising Moon's resources are either concentrated in the regolith, or occur in the regolith in the enriched condition ready for the extraction. The scope of the review embraces the structure of the lunar regolith and various methods to estimate its thickness, which can be used in combination depending on the objective to be reached. Each method has a certain area of estimation. It is also shown that the drilling depth down to 15 m is sufficient across the nearly entire Moon's surface and provides an ample stratifi ed geological column of the regolith starting from the base rock formation. All extraterrestrial resources are divided into two basic categories. The first category includes resources required for the industrial use on the spot. The second category of the extraterrestrial resources are the materials, crude or elements that are in deficit or absent on the Earth, and their extraction and shipment to the Earth can be profitable. Under discussion are volatile gas components that are divided into three basic types depending on the mechanism of retention and the form of occurrence in the regolith - implanted, loosely bound and frozen volatile matter. Implanted gases are resistant to mechanical impact and temperature in the range of several hundred degrees. Weakly bound gases that pervade pore space of the lunar regolith, on the opposite, readily escape under thermal and mechanical attacks on the regolith. Frozen volatile gases are in open pore space of the lunar regolith and are intolerant relative to mechanical and temperature effects. The article shows that extraction of weakly bound and frozen volatile matter featuring weak concentration and availability is impossible using the classical technology of excavation, transportation and heating of the lunar soil. In the capacity of the most promising technology for the development of the Moon's resources, the controllable selective extraction of gases from the natural and industrial silicates using electromagnetic resonance is considered.

Application of Thermodesorption Mass Spectrometry for Studying Proton Water Formation in the Lunar Regolith

Article

Full-text available

Jan 2017

In this paper, we report experimental data on the implantation of hydrogen ions of different energies into crystalline quartz samples. It was shown that irradiation with protons with an energy of 20 keV produces an amorphous film on the surface of a quartz sample, and irradiation with 90-keV protons results in the formation of a layer with interstitial defects and an increase in the unit-cell parameter of quartz with preservation of the crystal structure of the disturbed layer. The examination of the samples by thermodesorption mass spectrometry showed that high-energy irradiation resulted also in loosening of the surface layer and considerable expansion of high-potential adsorption sites, which was the reason for the observed peak desorption of gases. The existence of desorption peaks allowed us to calculate the activation energy of surface desorption of gas components. It was also found that an increase in irradiation energy tends to enhance the total degassing of samples.

Distribution of implanted hydrogen in amorphous silicon dioxide α-SiO2

Article

Full-text available

Jan 2004

Deuterium and Helium-3 in the Protosolar Cloud

Article

Jan 2000

New measurements of the isotopic composition of helium in the solar wind obtained from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses are presented and compared with earlier SWICS results and previous mass spectrometric determinations of this ratio with the Apollo Solar Wind Composition (SWC) experiment and the Ion Composition Instrument (ICI) on the International Sun Earth Explorer 3 (ISEE 3). The new SWICS data from both the fast and slow solar wind are extrapolated to the photosphere to obtain a representative value of the present-day ratio of 3 He/ 4 He = (3.75 ± 0.27) × 10 −4 in the Outer Convective Zone (OCZ) of the Sun. After corrections of this ratio for secular changes caused by diffusion, mixing and 3 He production by incomplete H-burning (Vauclair 1998), we obtain (D + 3 He)/H = (3.6 ± 0.38) × 10 −5 for the Protosolar Cloud (PSC). Adopting the Jovian 3 He/ 4 He ratio = (1.66 ±0.05) × 10 −4 measured by the Galileo Probe mass spectrometer (Mahaffy et al. 1998) as representative for the PSC, we obtain (D/H) protosolar = (1.94 ±0.39) × 10 −5 . Using results of galactic evolution studies (Tosi 1998, 2000) and the D and 3 He abundances in the Protosolar Cloud and the Local Interstellar Cloud (Linsky 1998; Gloeckler &Geiss 1998), we estimate (D/H) primordial = (2.4 − 4.2) × 10 −5 . This range corresponds to a universal baryon/photon ratio of (5.9−4.2) × 10 −10 .

Helium-3 on the moon: Model assumptions and abundances

Article

Jan 1994

Lawrence A. Taylor

Solar-wind particles are present in the outer few 100 angstroms of each soil particle of the Moon. Of particular interest, are the volatiles hydrogen (40-100 ppm) and helium (5-45 ppm). The potential use of D-3He fusion for energy generation requires a ready supply of 3He, and there is a distinct paucity of this on Earth. However, compared to the Earth, the Moon is a virtual `oasis with springs of solar-wind helium.' Conservative estimates of the helium contents of the regolith are 3 ppb (5.4 mg/m3) of 3He for the highland areas and 6 ppb (10.8 mg/m3) for the maria. This would require the mining of about 300 mare football fields per year, an area of 1.5 km2 (<400 acres), to a depth of 3 m, to supply sufficient 3He for a 500 MW fusion D-3He plant.

Clementine images of the lunar sample-return stations: Refinement of FeO and TiO 2 mapping techniques

Article

Jan 1997

Clementine UVVIS images of the lunar sample-return sites have been processed and used to produce refined calibrations for the iron and titanium determination algorithms of Lucey et al. [1995, 1996]. The high spatial resolution of the Clementine data permits individual sampling stations to be resolved at the Apollo 15, 16, and 17 landing sites. We find an excellent, linear correlation between the spectral Fe and Ti parameters and the average FeO and TiO 2 contents of soils sampled at each site or station. This correlation demonstrates that these techniques can confidently be applied to other areas of the Moon. The Luna 24 site does not fit the Ti relation found for other sites, suggesting that either its sample is nonrepresentative or the reported landing coordinates are incorrect.

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