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Volatile Analysis by Pyrolysis of Regolith for Planetary Resource Exploration

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The extraction and identification of volatile resources that could be utilized by humans including water, oxygen, noble gases, and hydrocarbons on the Moon, Mars, and small planetary bodies will be critical for future long-term human exploration of these objects. Vacuum pyrolysis at elevated temperatures has been shown to be an efficient way to release volatiles trapped inside solid samples. In order to maximize the extraction of volatiles, including oxygen and noble gases from the breakdown of minerals, a pyrolysis temperature of 1400ºC or higher is required, which greatly exceeds the maximum temperatures of current state-of-the-art flight pyrolysis instruments. Here we report on the recent optimization and field testing results of a high temperature pyrolysis oven and sample manipulation system coupled to a mass spectrometer instrument called Volatile Analysis by Pyrolysis of Regolith (VAPoR). VAPoR is capable of heating solid samples under vacuum to temperatures above 1300ºC and determining the composition of volatiles released as a function of temperature.
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1
The extraction and identification of volatile resources
that could be utilized by humans including water, oxygen,
noble gases, and hydrocarbons on the Moon, Mars, and
small planetary bodies will be critical for future long-term
human exploration of these objects. Vacuum pyrolysis at
elevated temperatures has been shown to be an efficient
way to release volatiles trapped inside solid samples. In
order to maximize the extraction of volatiles, including
oxygen and noble gases from the breakdown of minerals, a
pyrolysis temperature of 1400ºC or higher is required,
which greatly exceeds the maximum temperatures of
current state-of-the-art flight pyrolysis instruments. Here
we report on the recent optimization and field testing
results of a high temperature pyrolysis oven and sample
manipulation system coupled to a mass spectrometer
instrument called Volatile Analysis by Pyrolysis of
Regolith (VAPoR). VAPoR is capable of heating solid
samples under vacuum to temperatures above 1300ºC and
determining the composition of volatiles released as a
function of temperature.
Keywords Evolved gas analysis, Desert Research And
Technology Studies (DRATS), Lunar volatiles, Mass spectrometry,
Planetary science, Resource utilization, Vacuum pyrolysis, Volatile
Analysis by Pyrolysis of Regolith (VAPoR)
I. INTRODUCTION
Measuring the chemical composition of planetary bodies
and their atmospheres is key to understanding the formation of
the Solar System and the evolution of the planets and their
moons. Moreover, in situ volatile measurements would enable
a ground-truth assessment of the availability of resources such
as water and oxygen, important for a sustained human
presence on the Moon and beyond. Recent data from the
Lunar CRater Observation and Sensing Satellite (LCROSS)
Copyright 978-1-4577-0557-1/12/$26.00 ©2012 IEEE
revealed spectroscopic evidence for water-ice in the impact
plume from Cabeus crater at a level corresponding to ~ 6 wt %
water-ice [1]. Several other volatiles including light
hydrocarbons, sulfur bearing species, and carbon dioxide were
also detected in the impact plume by LCROSS [1]. The
detection of water-ice by LCROSS was consistent with
previous observations by Clementine and the Lunar Prospector
spacecraft showing that the lunar polar regions contain
enhanced levels of hydrogen, a potential signature of water-ice
[2]. One explanation for the presence of enhanced volatiles at
the lunar poles is the delivery of water and other volatile
species to the lunar surface by repeated cometary and asteroid
impacts during the late heavy bombardment period ~4.1-3.8
Ga [3], followed by migration and concentration of the
volatiles in permanently shadowed cold traps. Another
possible source for some of the volatiles detected at the lunar
poles, particularly hydrogen, is implantation by the solar wind.
Any solar wind implanted hydrogen or volatiles in the surface
regolith that migrate to the polar regions would be delayed
from diffusing out of the permanently shadowed regolith by
the extremely low temperatures [4].
Although the volatile content of lunar samples recovered
from the equatorial regions of the Moon during the Apollo
missions has been well studied [5-9], to thoroughly
characterize the volatile abundance, distribution, and isotopic
composition of regolith at the lunar poles, in situ analyses by
pyrolysis instruments with high resolution mass spectrometers
will be required to fully quantify the presence and composition
of the volatiles. To date, there have been no in situ volatile
measurements on the Moon using pyrolysis mass
spectrometry. The Lunar Atmosphere Composition
Experiment (LACE) mass spectrometer on Apollo 17, did
make surface volatile measurements of the tenuous lunar
exosphere, but it was not equipped with pyrolysis ovens for
evolved gas measurements of the regolith [10].
Vacuum pyrolysis is the most efficient way to release the
Volatile Analysis by Pyrolysis of Regolith for Planetary
Resource Exploration
Daniel P. Glavin
1*
, Charles Malespin
1,2
, Inge L. ten Kate
3
, Stephanie A. Getty
1
, Vincent E. Holmes
1,4
, Erik
Mumm
5
, Heather B. Franz
1,6
, Marvin Noreiga
1,7
, Nick Dobson
1,8
, Adrian E. Southard
1,2
, Steven H. Feng
1
, Carl A.
Kotecki
1
, Jason P. Dworkin
1
, Timothy D. Swindle
9
, Jacob E. Bleacher
1
, James W. Rice
1
, and Paul R. Mahaffy
1
1
NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA;
2
University Space Research Associates, 10211
Wincopin Circle, Columbia, MD 21044, USA;
3
University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway;
4
Bastion Technologies,
Lanham, MD 20706, USA;
5
Honeybee Robotics, 460 W. 34
th
Street, New York, NY, 10001, USA;
6
Center for Research and Exploration in
Space Science and Technology, 5523 Research Park Drive, University of Maryland Baltimore County, Baltimore MD 21228, USA;
7
ADNET Systems, Inc., 164 Rollins Ave., Rockville, MD 20852, USA;
8
Northrup Grumman Corporation, 2980 Fairview Park Drive, Falls
Church, VA 22042, USA;
9
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
*Corresponding author email: daniel.p.glavin@nasa.gov
charles.a.malespin@nasa.gov, science@ingeloes.com, stephanie.a.getty@nasa.gov, vincent.e.holmes@nasa.gov,
mumm@honeybeerobotics.com, heather.b.franz@nasa.gov, marvin.g.noreiga@nasa.gov, nick.dobson@gmail.com,
adrian.e.southard@nasa.gov, steven.h.feng@nasa.gov, carl.a.kotecki@nasa.gov, jason.p.dworkin@nasa.gov, tswindle@u.arizona.edu,
jacob.e.bleacher@nasa.gov, james.w.rice@nasa.gov, and paul.r.mahaffy@nasa.gov
2
widest range of volatiles from regolith samples, especially if
the sample has been crushed prior to heating [11]. It has been
shown previously in laboratory measurements that 90% of the
volatile materials in Apollo samples can be released by
pyrolysis stepped heating to 1400ºC [6]. Many of the key
volatiles of interest for planetary resource exploration can be
extracted at temperatures of 1000ºC or less (see Table 1).
However, vacuum pyrolysis experiments of lunar simulants
show that O
2
can only be released at temperatures greater than
1200ºC [12]. In addition, the release of the noble gases Ne,
Ar, Kr, and Xe trapped in higher temperature mineral phases
requires stepped heating to temperatures up to 1400ºC [13,
14]. Although other approaches have been used for the
extraction of volatiles, including mechanical agitation [15] and
laser heating [16], vacuum pyrolysis using a stable controlled
heating ramp coupled with mass spectrometry will enable
evolved gas measurements that can be used to determine the
volatile distribution in a solid sample and provide important
constraints on bulk chemistry and mineral composition.
Table 1. Release temperatures of gases targeted by the VAPoR
pyrolysis mass spectrometer instrument for compound identification
and isotopic analyses.
[17]
VAPoR target gases Temperature range (°C)
CHONS-
Inorganics
Atmospheric volatiles Not applicable
H
2
O, H
2
, CO
2
, CO, N
2
, SO
2
0-1400
[6, 7, 18]
13
C/
12
C ratio of CO
2
100-1400
[18]
15
N/
14
N ratio in N
2
600-1400
[18]
HDO/H
2
O ratio 0-1400
Noble
Gases
He, Ne, Ar 300-1400
[18, 19]
Isotope ratios (
3
He/
4
He,
36
Ar/
40
Ar)
He: 200-500
[5]
Ar: 300-1400
[18, 20]
Organics
13
C/
12
C ratio in CO
2
from
organics combustion
400-500
[19]
Volatile hydrocarbons:
methane, ethane, benzene,
amines, alcohols,
formaldehyde
300-1000
[18]
Other
Resources
Water-ice in regolith 0-100
O
2
1100-1400
[5]
Reduced inorganic gases
such as HCN, NH
3
, and
H
2
S
HCN/NH
3
: 100-900
[18]
H
2
S: 700-1300
[6]
3
He relative abundance He: 200-500
[5]
3
He relative abundance He: 200-500
[5]
Several previous and current flight instruments used the
pyrolysis approach to extract volatiles from solid regolith
(summarized in Table 2). The Viking landers each carried a
gas chromatography mass spectrometry (GCMS) instrument
equipped with three ovens capable of heating regolith samples
at different temperatures up to 500ºC [21, 22]. More recently,
the Thermal and Evolved Gas Analyzer (TEGA) instrument
on the Phoenix Mars lander heated polar regolith samples up
to 950ºC and analyzed the evolved gases using a mass
spectrometer [23]. The Rosetta mission, currently on its way
to comet 67P/Churyumov-Gerasimenko, includes two evolved
gas mass spectrometer instuments, the Cometary Sampling
and Composition (COSAC) experiment [24] and Ptolemy
[25]. These instruments contain very small pyrolysis ovens,
capable of heating samples to 600ºC and 800ºC, respectively.
Most recently, the Sample Analysis at Mars (SAM) instrument
suite on the Mars Science Laboratory (MSL) mission that is
scheduled to launch in 2011 contains two separate pyrolysis
ovens, each capable of being heated up to 950-1100ºC for
volatile analysis of solid samples by GCMS and tunable laser
spectroscopy [26]. None of these current flight ovens are
designed to heat solid samples to temperatures above 1100ºC
as required to release the full range of volatiles from planetary
samples (Tables 1 and 2).
Future robotic missions to remote planetary surfaces will
likely be highly resource-constrained and will require smaller
and simpler instrumentation than their predecessors.
Therefore, the development of lower mass and power evolved
gas mass spectrometer instruments that maintain or exceed the
performance of previous instruments will be a key challenge
for upcoming missions. The Volatile Analysis by Pyrolysis of
Regolith (VAPoR) instrument is a simplified version of its
predecessor SAM, and enables compositional and isotopic
measurements of volatiles in planetary atmospheres and
exospheres and released from solid surface samples using
pyrolysis mass spectrometry on airless bodies including the
Moon, asteroids and comets, and the icy moons of the Outer
Planets [17]. With the addition of a miniature turbo pump,
VAPoR could also operate in higher pressure planetary
environments including Mars and Titan.
Table 2. Comparison of VAPoR to current planetary flight instrument
pyrolysis systems and their temperature profiles.
[17]
Viking
[22]
TEGA
[23]
COSAC
[24]
Temperature
range
50, 200, 350,
and 500 °C
Ambt. to 950 °C Ambt. to 600°C
Oven
materials
Ceramic. Nickel.
Platinum resistance
wire.
Ceramic coating.
Platinum.
Platinum
resistance wire.
Glass.
Oven/cup size
diameter
length
volume
2 mm
19 mm
60 mm
3
7.2 mm
21.6 mm
38 mm
3
(sample)
3 mm
6 mm
42 mm
3
Number of
ovens
3 8 2
Ptolemy
[25]
SAM
[26]
VAPoR
Temperature
range
Ambt. to
800°C
Ambt. to ~1000°C Ambt. to
1400°C
Oven
material
Platinum.
Platinum
resistance
wire.
Glass.
Inconel 693 tube
surrounded by
alumina sleave.
ZGS Platinum-10%
Rhodium resistance
wire.
Alumina
crucible.
ZGS Platinum-
10% Rhodium
resistance wire.
Oven/cup size
diameter
length
volume
3 mm
6 mm
42 mm
3
7 mm I.D. (qtz. cup)
20.5 mm (qtz. cup)
789 mm
3
(qtz. cup)
6.2 mm I.D.
18.2 mm
539 mm
3
Number of
ovens/cups
3 2 ovens, 74 sample
cups (qtz./inconel)
6
Abbreviations: Ambt., ambient temperature; I.D., internal diameter; qtz.,
quartz; ZGS, zirconium grain strengthened
The preliminary VAPoR flight instrument concept (Fig.
1) combines a sample carousel of up to six individually heated
pyrolysis ovens with a reflectron time of flight mass
spectrometer [27]. The VAPoR gas processing system
includes two gas manifolds, heated transfer lines, and two
separate gas reservoirs for calibration of the mass
3
spectrometer and oxygen for combustion experiments.
Powdered rock or soil samples collected from a rover or
lander drill or scoop and delivered through the solid sample
tube to one of the VAPoR ovens can then be heated by a
controlled ramp from ambient to temperatures up to 1400ºC to
release the volatile constituents for direct measurement by the
mass spectrometer. Two independent units have been built
and tested to understand the performance of the different
instrument components. A laboratory breadboard was
developed to test, optimize, and calibrate the reflectron time of
flight mass spectrometer (TOF-MS) component of VAPoR
inside a separate vacuum chamber and is discussed in more
detail in Section V and elsewhere [27]. A separate portable
field unit consisting of a custom made pyrolysis oven coupled
to a commercial RGA quadrupole mass spectrometer, vacuum
manifold and turbomolecular pumping station, was built to
demonstrate the feasibility of conducting vacuum pyrolysis
evolved gas measurements in the field and has been discussed
previously [17].
Fig. 1. Cross sectional view of the preliminary VAPoR flight instrument
concept which combines a sample carousel containing six separate pyrolysis
ovens integrated to a reflectron time of flight mass spectrometer for volatile
analyses on the surface of planetary bodies throughout the Solar System.
The focus of this paper will be on the high temperature
pyrolysis oven and six-position oven carousel components that
were recently integrated to the VAPoR field instrument (Fig.
2). Here we will describe the VAPoR instrument and key
science measurement objectives enabled by high temperature
pyrolysis, provide details on the new oven and carousel
designs, and present recent experimental results obtained
during NASA's 2011 Desert Research And Technology
Studies (DRATS) field campaign at Black Point Lava Flow in
Arizona.
II. I
NSTRUMENT AND ANALYTICAL PROTOCOL
A. Science Measurement Objectives
There are at least four key planetary science and resource
exploration measurement objectives that can be achieved
using VAPoR: (1) confirm the abundances of water detected
on the Moon by LCROSS [1] and discriminate between
adsorbed water, water-ice, and water released from hydrated
minerals; (2) measure the distribution and isotopic (D/H ratio)
composition of water and the presence of other volatiles
including hydrocarbons to establish their origin(s), (3)
measure the total abundances of oxygen released by
breakdown of silicate minerals during high temperature
pyrolysis for large-scale in situ resource utilization technology
development, and (4) contribute to in situ geochronology by
thermal extraction of argon and
40
Ar measurements needed for
K-Ar radiometric age dating [28].
VAPoR will focus on the analyses of C, H, O, N, and S
containing volatiles commonly released from minerals,
including H
2
O, CO
2
, CO/N
2
, and SO
2
. The pyrolysis
temperature profile was optimized for the detection of simple
aliphatic and aromatic hydrocarbons such as methane, ethane,
benzene, and alkylbenzene. In addition, VAPoR will measure
the distribution and isotopic composition of the noble gases
He, Ne, and Ar. These measurements are important for
understanding the contribution of noble gases from solar wind
implantation and cosmic ray bombardment and potentially
even outgassing from the interior of a planetary body.
Measurements of
40
Ar extracted from rock samples by VAPoR
high temperature pyrolysis is also important for K-Ar age
dating if K abundances can be derived by another
measurement technique. An overview of the target volatiles
of VAPoR and their release temperatures is given in Table 1.
B. VAPoR Field Instrument Description
The VAPoR field instrument tested during DRATS
shown in Figure 2 consists of a six-port stainless steel vacuum
manifold (MDC Vacuum Products) connected to a six-position
sample manipulation system (SMS, Honeybee Robotics)
containing two custom made high temperature pyrolysis ovens
developed at NASA Goddard Space Flight Center (GSFC).
Fig. 2. The VAPoR field instrument, which includes a new sample
manipulation system and high temperature pyrolysis oven for evolved gas
analysis of powdered solid samples.
The vacuum manifold is also connected to an atmospheric
gas inlet (MDC precision leak valve), a cold cathode ion
pressure gauge (Pfeiffer Vacuum PKR 251), and a residual gas
analyzer (Stanford Research Systems, RGA 300, mass range:
1-300 amu), and is actively pumped using a turbomolecular
pumping system (Pfeiffer Vacuum TSU071E, TC600). A 30V
power supply (Sorensen DLM 20-30) is used to power the
4
ovens and a separate control unit (Honeybee Robotics) is used
to power and command the SMS. Two Watlow EZ Zone
temperature controllers are used to control the pyrolysis oven
ramp rate (set at 20ºC/min) and manifold heater temperature
(set at 50ºC).
A ruggedized laptop computer (Panasonic
Toughbook) with a custom Labview platform is used to
control the RGA and collect mass spectrometer, oven voltage
and current, and oven temperature data obtained from the
instrument. The instrument is set up to enable direct line of
sight from the heated sample in an oven to the ionization
region of the RGA mounted at the top of the manifold. The
RGA was setup to scan over the mass range 1-100 amu during
the pyrolysis heating experiment. The current VAPoR field
instrument does not include the TOF-MS, which is being
tested and optimized separately in a larger vacuum chamber at
NASA GSFC (Section V).
C. Solid Sample Analysis Protocol
A sample collection and analytical protocol was
developed for the VAPoR field instrument prior to NASA's
2011 DRATS field test. The mortar and pestle, stainless steel
spatulas, glass vials, quartz sample holders and glass wool
used in sample preparation and storage were all baked at
500ºC in air for 3 h. Rock and soil samples were collected by
crewmembers in the field using clean metal tongs or shovels.
Samples were subsequently wrapped in ultrahigh vacuum foil
(All-Foils, Inc.) prior to bagging inside polyethylene bags
(Whirl-Pak) in order to minimize hydrocarbon contamination
of the samples during the collection process. This approach
eliminated direct contact between the sample and the bags or
gloves of the crewmembers, as commonly occurs during the
standard sample collection procedure used during DRATS
[29]. Photodocumentation and preliminary microscopic
imaging analyses of the samples were conducted inside the
DRATS Geolab [30], which is a glovebox located inside
NASA’s Habitat Demonstration Unit that is designed for
scientific analyses of samples collected during a mission.
During the field test VAPoR was a standalone instrument
physically located outside of the Geolab and subsequent to the
standard crew analyses a small fragment of each sample was
chipped off for VAPoR evolved gas measurements. One of
the Geolab samples studied by VAPoR (sample 0212, Fig. 3)
was a vesicular basalt containing up to 3 mm diameter
vesicles. Results from the evolved gas analysis of a small
fragment of this sample is discussed in Section IV.
Fig. 3. Image of rock sample 0212 processed in the Geolab and analyzed by
VAPoR. Sample 0212 is a vesicular basalt fragment covered with light brown
soil with a total mass of 156 g (photo credit: NASA).
Prior to VAPoR analysis, each sample fragment was
crushed using a ceramic mortar and pestle and the resulting
powder passed through a stainless steel metal sieve (ASTM
No. 100, < 150 m). The sieved powder was transferred into
a clean 8 ml screw capped glass vial using a stainless steel
spatula. Since many rock samples will melt inside the oven
crucible when heated to temperatures above 1200°C, the rock
powders (~ 10 mg) were each loaded inside a separate quartz
tube sample holder (3 mm ID, 5 mm OD, ~ 25 mm length)
packed with quartz glass wool at the bottom, and the entire
quartz holder was inserted into the VAPoR oven (see Fig. 4).
Although the VAPoR pyrolysis oven can handle much
larger sample sizes (up to ~ 1 gram), we have found that at
elevated temperatures, samples with masses over 10 mg can
lead to high manifold pressures (> 10
-4
mbar) during pyrolysis,
which prohibits the use of the mass spectrometer during the
evolved gas measurements. A < 150 m fused silica powder
(120/P, Precison Electro Minerals Co., Inc.) that had been
baked in air for 6 h at 900ºC was used as a procedural blank to
characterize the background of volatiles in the VAPoR system
during a solid sample pyrolysis experiment. The fused silica
powder was also used in the solid sample temperature
calibration experiments to determine the relationship between
the oven ramp temperature and the actual temperature of a
sample inside the quartz tube holder (see Section IIIB).
Fig. 4. Diagram of the main components of the high temperature pyrolysis
oven custom made for the VAPoR field instrument. Solid samples are placed
inside quartz tube sample holders (right inset), which are then inserted directly
into the alumina oven crucible for evolved gas analysis. For the flight
instrument, solid samples would be dropped by an astronaut or robotic sample
acquisition system through an inlet tube directly into the alumina crucible.
After each quartz sample tube is loaded with a sample, the
SMS is rotated into the sample receive position that places the
oven directly beneath the solid sample inlet tube port. The
quartz tube is then dropped inside the alumina crucible oven
as illustrated in Figure 4. The oven is then rotated by the SMS
into the pyrolysis position directly under a knife-edge
interface to the vacuum manifold (additional details on SMS
in Section IIID). The pyrolysis oven is raised up to engage the
SMS knife-edge interface and create a vacuum tight knife-
edge seal on the inner copper gasket on the top flange of the
oven. After sealing, the turbo pump is started and allowed to
spin up to 1500 Hz. The vacuum manifold is pumped down to
a pressure of ~10
-7
to 10
-8
mbar prior to pyrolysis oven
5
heating. In this pressure range, the RGA is turned on and the
filament left on for 15 minutes to warm up. The oven power
leads are connected from the power feedthroughs on the base
of the oven directly to the front panel of the power supply and
the oven set to an initial temperature of 50ºC.
For each EGA measurement, the pyrolysis oven crucible
was heated at a controlled rate of 20ºC/min from 50ºC up to
1000ºC using the Watlow temperature controller based on type
C thermocouple temperature measurements of the bottom of
the alumina crucible (Fig. 4 left). Previous evolved gas
measurements have shown that ramp rates of 20ºC/min or less
are desired for sufficient time separation of volatiles released
from the sample required for improved volatile mass
identification. It should be noted that at 1000ºC, the actual
temperature inside the oven that the sample is heated to is
much higher than the measured oven temperature based on
direct type C thermocouple measurements of the inside of the
quartz sample holder made in separate experiments (discussed
in Section IIIB). The vacuum manifold was kept at 50ºC
through the entire pyrolysis experiment to keep water and
other volatiles from condensing on the internal surfaces of the
manifold.
While ramping the oven, analyses of the volatiles
released from the sample were made by the RGA quadrupole
mass spectrometer by repeated unit mass scans (mass range 2
to 100 Da) throughout the pyrolysis experiment. The
sensitivity of the faraday cup collector used in the RGA is 2 x
10
-4
A/Torr and the measured current for each mass/charge
(m/z) ratio is converted to a partial pressure (Torr) and stored
in LabView. Each individual mass can then be plotted
separately as a function of oven temperature in LabView to
obtain an evolved gas plot. In addition to the primary volatile
components typically released from terrestrial samples (water,
carbon dioxide, sulfur dioxide, and nitrogen/carbon
monoxide), we are also interested in identifying characteristic
mass fragments of simple aliphatic (e.g., m/z 27, 43, 55, 57)
and aromatic (e.g., m/z 78, 91) hydrocarbons released from the
samples. The unit mass resolution of the RGA was not
sufficient to measure the isotopic ratios of C, N, and H in the
volatiles released; however future integration of a higher mass
resolution TOF-MS to the VAPoR pyrolysis oven should
greatly improve current capability.
III. PYROLYSIS OVEN AND CAROUSEL MECHANISM
A. Oven Design
The VAPoR pyrolysis oven (Fig. 4) was designed to bring
the sample to a maximum temperature of 1400
o
C to release
volatiles for direct mass spectrometer analysis. In contrast to
the SAM instrument ovens [26], where quartz or metal cups
containing the solid sample are inserted into an inconel tube
surrounded by a platinum wire threaded alumina insulator, the
VAPoR alumina oven crucible is the cup. This enables more
efficient and direct heating of a solid sample placed at the
bottom of the crucible. Like SAM, the VAPoR oven uses a
zirconium grain strengthened (ZGS) platinum-rhodium alloy
wire (0.51 mm) as the heater. This wire is threaded up and
down through small channels in a custom-made alumina
crucible (Technology Assessment and Transfer, Inc.) with an
internal volume of 539 mm
3
. The VAPoR alumina crucibles
are designed to hold up to ~1 gram of sample powder
(assuming a density of 2 g/cm
3
). As discussed previously,
VAPoR requires only a very small volume of sample (~ 5
mm
3
or ~ 10 mg) for each evolved gas analysis, which means
that each oven can be refilled multiple times for over 100
evolved gas analyses before the crucible volume is completely
full. However, it should be noted that the power required to
heat a full oven would be substantially higher than in an oven
containing a single 5 mm
3
sample volume aliquot.
In order to minimize the power required to heat a sample,
a set of four evenly spaced rhenium-coated precision-
fabricated molybdenum vertical radiation shields surround the
alumina crucible. In addition, a stack of ten custom made
tungsten shields located below and above the alumina crucible
is also used to improve the thermal design of the oven. To
minimize the heat loss through the bottom of the crucible, an
inconel bellows support structure is used. The entire oven
assembly is housed inside a standard 2.75 in. stainless steel
304 flange and nipple assembly so that the oven can be
mounted and sealed directly to the VAPoR vacuum manifold
via a copper gasket and knife-edge. The bottom flange of the
oven was modified to include a set of two copper power
feedthroughs as well as two type C thermocouple
feedthroughs (not seen in Fig. 4 cross-section). The platinum-
rhodium heater wire is connected directly to the power
feedthroughs and a type C thermocouple wire (0.25 mm dia.)
connects from the thermocouple feedthroughs directly to the
base of the oven directly below the quartz sample tube. A
separate type C thermocouple was placed at the bottom of the
quartz tube and connected to type C thermocouple
feedthroughs in a separate flange mounted directly above the
oven at the top of the vacuum manifold. The thermocouple
inside the sample was only used during the sample
temperature calibration experiment and was removed during
actual pyrolysis EGA measurements given concern that some
of our samples would melt around the thermocouple at
temperatures above 1200ºC. In SAM, the ovens do not use
thermocouples to determine the temperature of the ovens
during pyrolysis heating, but instead the oven temperature is
derived from the resistance of a second platinum heater wire
threaded through the alumina insulator.
Based on SAM pyrolysis oven testing, and the fact that
the volume heated by the VAPoR oven is smaller than in the
SAM ovens (Table 2), we expect that the VAPoR oven would
achieve maximum sample temperatures of 1400°C with a
power consumption that is less than the equivalent power
consumption of the SAM flight ovens at the same temperature
(~ 36 W at 950°C for SAM). Furthermore, in the SAM oven
design the temperature of a sample inside a cup is ~ 50-100°C
lower than the external platinum wire temperature as
determined by thermocouple measurements of the interior of
the quartz cup. Therefore with the SAM ovens, the power
required to get the sample to 950°C would likely be higher
than 36 W.
B. Solid Sample Temperature Calibration
In order to determine the relationship between the oven
temperature measured from the bottom of the crucible and the
actual temperature that a powdered sample reaches inside the
quartz sample holder, we mounted a second type C
6
thermocouple to the top of the VAPoR vacuum manifold cross
so that the end of the thermocouple was located directly inside
the quartz sample holder filled with 10 mg of fused silica at
the bottom of the oven crucible (Fig. 4). The oven crucible
was then heated at a controlled ramp rate of 20°C/min from
ambient temperature up to 1000°C as measured by the
thermocouple located at the bottom of the crucible. During
the heating ramp we measured the oven crucible temperature,
the temperature inside the quartz tube with and without fused
silica, and the oven current and voltage. A plot of the oven
crucible temperature compared to the actual sample
temperature inside the quartz tube holder is shown below (Fig.
5).
Fig. 5. Plot showing sample temperature (ºC) vs. alumina oven temperature
(ºC) as measured with separate type C thermocouples during vacuum
pyrolysis of an empty quartz tube and quartz sample tube containing 10 mg of
fused silica powder after heating the oven at a pressure of ~10
-7
mbar to
1000ºC at a rate of 20ºC/min. The solid line represents the case where the
sample temperature inside the quartz tube is identical to the temperature of the
bottom of the alumina crucible. The dashed line is the polynomial best fit of
the temperature of the fused silica sample as a function of oven temperature.
The thermocouple data show that when there was no solid
sample inside an empty quartz holder, the temperature inside
the quartz tube was significantly higher (~100-200°C) at
temperatures above 200°C than the temperature measured at
the bottom of the alumina crucible. This is likely due to the
fact that the platinum-rhodium heater wires are wrapped
predominately around the sides of the alumina crucible and
most of the oven-generated heat is reflected directly to the
center of the crucible by the vertical and horizontal shielding
(Fig. 4). We also observed a significant sample temperature
lag of ~ 100°C at lower temperatures compared to the oven
crucible temperature when 10 mg of fused silica powder was
placed inside the quartz sample holder. A much slower ramp
rate than the 20ºC/min ramp rate used in these experiments
would be required to reduce this measured sample temperature
lag. At ~600°C the sample temperature and oven temperature
reached equilibrium; however, above 600°C the sample
temperature increased rapidly up to a temperature of ~1300°C
(Fig. 5), greatly exceeding the temperature measured at the
bottom of the crucible (1000°C). Although the platinum-
rhodium heater wire used in the crucible could be heated to
higher temperatures (up to 1400°C), we stopped the
experiment at a sample temperature of ~1300°C to ensure that
we did not melt the quartz sample tube and risk damage to the
alumina crucible.
Since we did not measure sample temperature directly
during an actual evolved gas analysis run (many rock samples
will melt at 1300°C and could destroy the thermocouple), the
fused silica sample temperature data was fit (Fig. 5 dashed
line) to a polynomial function. Through a comparison of the
polynomial fit to repeated actual sample temperature
measurements, we have found that the sample temperature can
be calculated directly from the measured oven crucible
temperature with an accuracy of ± 5°C over the entire
temperature range. It should be noted that the relationship
between sample temperature and oven temperature was
determined for a 10 mg sized fused silica sample and samples
with a different mineral composition or with larger masses
might not follow the same polynomial fit.
C. Oven Power Data
In order to determine the power required to heat a solid
sample, the oven current and voltage were measured as a
function of oven temperature during each pyrolysis EGA run.
The oven temperature was then converted to sample
temperature based on a polynomial fit and the sample
temperature then plotted vs. oven power (W). In Figure 6,
plots of the oven power vs. calculated sample temperature are
shown for the empty quartz holder and the quartz tube
containing 10 mg of fused silica. We found that a peak power
of 64 W was required to heat the inside of the quartz tube up
to a temperature of 1300°C and ~60 W continuous power (15
V, 4 A) was required to maintain that temperature. A slightly
higher power (~ 70 W peak) was required to heat up the fused
silica powder to the same temperature as the empty quartz
tube, which is probably due to a higher mass in the oven
crucible.
Fig. 6. Plot showing the peak power consumption (W) as a function of
calculated sample temperature (ºC) of the alumina oven containing an empty
quartz tube and a quartz tube filled with 10 mg of fused silica powder. The
oven was heated at ~10
-7
mbar to 1000ºC at a rate of 20ºC/min.
To reach a temperature of 950°C, only 33 W of power
was required for the VAPoR oven, which is less power than
required by SAM pyrolysis at the same temperature. Based
upon the power trends measured for the VAPoR oven (Fig. 6),
we estimate that ~75-80 W of power would be required to heat
7
a 10 mg solid sample to 1400ºC, although less continuous
power would be required to maintain that temperature.
Further optimization of the VAPoR oven design including the
addition of alumina insulating material at the base of the
Inconel 693 bellows support structure could help reduce heat
loss from the base of the oven.
D. Oven Carousel Design
The sample manipulation system (SMS) developed for
VAPoR is a two degree of freedom robotic system capable of
accommodating up to six independent pyrolysis ovens (Fig.
7). A similar SMS concept was developed for the SAM
experiment on the MSL mission which contains a total of 74
sample cups that can also accept solid sample through a solid
sample inlet tube (SSIT) and then be raised individually inside
one of two stationary pyrolysis ovens and sealed inside the
oven using a knife-edge against a copper gasket on the cup
stem. Unlike SAM, in the VAPoR SMS design the entire
pyrolysis oven is rotated and sealed directly to the mass
spectrometer vacuum manifold. One degree of freedom
rotates the carousel to position a selected pyrolysis oven
directly beneath the mass spectrometer vacuum manifold or
the SSIT.
The second degree of freedom raises and lowers the
carousel as well as the cleats which preload an annealed
copper gasket brazed to the top flange of the oven into a 1055
medium carbon steel knife-edge seal at the manifold location.
The seal force has an accuracy of
±
10% and was designed to
provide repeated leak tight (< 1 x 10
-5
cc He/sec) seals at the
oven manifold interface. Both degrees of freedom are
actuated via the same gearmotor. A toggle/clutch mechanism
dictates whether the gearmotor rotates or elevates the carousel.
Fig. 7. A cross sectional view of the VAPoR SMS mechanical design (left)
and fully assembled SMS hardware containing one pyrolysis oven (right) prior
to integration to the field instrument.
Although a solid sample inlet tube was included in the
VAPoR flight instrument concept, this component was not
integrated to the VAPoR SMS. The sample reservoir shown
in the mechanical design (Fig. 7, left) can be utilized as a
"trash-can" for excess sample inside the SSIT, but is not
included in the current SMS hardware. The SMS also
includes a plastic enclosure to protect the moving parts within
the SMS from dust contamination. The SMS control unit (Fig.
2) provides a graphical user interface to issue commands to
the SMS and monitor the system status. Fully autonomous
software routines allow the user to select between a stow, a
detach, and a pyrolysis sequence. The control system also has
the capability to direct power to a selected pyrolysis oven.
Thus, all pyrolysis oven electrical connections (power and
thermocouple leads) are self contained inside the SMS and the
control system ensures that only the oven selected for an
experiment is powered by the VAPoR power supply.
The stow routine preloads the carousel and the ovens into
the primary plate in the center of the SMS mechanism. The
purpose of the stow routine is to secure the system for
transport (field unit). This routine can also be used for a flight
instrument to secure the SMS and the pyrolysis ovens for
launch and roving operations during surface operations of a
landed mission. The pyrolysis routine sequences the system
through the steps necessary to load the sample into an oven
and initiate the pyrolysis heating sequence for an evolved gas
measurement. The routine first places the specified oven at
the sample inlet so that the sample quartz tube can be inserted
into the pyrolysis oven crucible. When the sample has been
delivered to the oven, the SMS rotates the carousel to place
the oven beneath the knife-edge at the vacuum manifold
interface to the mass spectrometer. Once in position, the
carousel lifts the oven into the knife-edge (Fig. 7, right inset)
and cleats on either side of the oven top flange preload the
copper gasket on the oven flange to the 1055 steel knife-edge
mounted to the manifold to create a leak tight seal.
Based on experience testing the SAM SMS, we decided to
issue the same command, regardless of the number of seals
that have been made with the oven. The nature of the steel
knife-edge on the annealed soft copper gasket is such that if a
sufficient amount of force is used, a seal can be made multiple
times without the need for incrementing the force on
successive seals. To date we have demonstrated over 20 leak
tight seals with the SMS on a single VAPoR oven, each
capable of holding a pressure of ~10
-8
mbar inside the oven
with active pumping. Although dust contamination of the
VAPoR could not be avoided in the field, the presence of dust
on the oven and SMS surfaces did not affect the ability to
obtain repeated leak tight seals. It should be noted that
VAPoR operation on the Moon or a different airless body
would not require a vacuum pump. However, a leak tight seal
to the oven provided by an SMS would still be desirable in
order to maintain gas pressure inside the mass spectrometer
for static measurements of noble gases and other trace volatile
components that would require much longer mass
spectrometer integration times to increase signal to noise.
Finally, the SMS detach routine allows for easy insertion
and removal of pyrolysis ovens without extensive disassembly
of the SMS. All routines were tested during the DRATS
campaign. The SMS successfully demonstrated robotic
pyrolysis experiments in the field. Samples collected by
DRATS crewmembers consisting of a team of astronauts and
geologists were crushed and sieved by the VAPoR team.
Approximately 10 mg of sample powder was transferred to a
quartz sample tube, the tube delivered to the pyrolysis oven
through the SMS sample inlet location and subsequently
sealed at the mass spectrometer interface, and the sample
pyrolyzed for evolved gas measurements by the RGA.
8
IV.
EVOLVED GAS MEASUREMENTS
Evolved gas data provided by VAPoR can be used to
select the most volatile-rich samples for large scale in situ
resource utilization (ISRU) and/or sample return. To establish
the volatile background inside the instrument, several
procedural blank measurements of the fused silica and empty
quartz sample tube and wool were made throughout the
DRATS field test. Evolved gas analysis (EGA) data from a
quartz tube procedural blank (Fig. 8) showed minor amounts
(< 3 x 10
-7
Torr) of H
2
O (m/z 18), CO/N
2
(m/z 28), and CO
2
(m/z 44), with only traces (< 4 x 10
-9
Torr) of aliphatic (m/z
27 and m/z 30) and aromatic hydrocarbon fragments (m/z 78),
and O
2
(m/z 32). Other procedural blanks ran in the field
yielded similar EGA results. The outgassing levels observed in
the procedural blanks were much lower than the partial
pressures of the same volatiles observed during pyrolysis of
samples collected in the field (~10
-5
to 10
-8
Torr range).
Fig. 8. Procedural blank background evolved gas profile of an empty quartz
sample holder heated to 1300ºC. Selected inorganic and organic volatiles
released from the sample as function of sample temperature. N
2
and CO and
cannot be separated with the RGA used and are therefore plotted together.
EGA data obtained from Geolab sample 0212, a vesicular
basalt collected from the Black Point Lava Flow in Arizona is
shown in Fig. 9. The primary volatile released between 300-
600ºC was CO
2
(m/z 44) derived from the breakdown of
carbonate minerals and possibly some oxidation of organic
matter in the sample. Hydrocarbons were released from the
sample at temperatures above 200ºC, consisting primarily of
alkanes as indicated by characteristic alkane hydrocarbon
fragment peaks at m/z 27 and m/z 30. Only trace levels of
aromatic hydrocarbons (m/z 78, benzene) were detected in the
sample. Some of these organics were released over the same
temperature range as the carbonate mineral decomposition and
therefore may have been trapped within the carbonate mineral
matrix.
The water (m/z 18) peaks indicate the presence of
multiple hydrated mineral phases, possibly hydrous oxides or
phyllosilicates as well as hydrated sulfate minerals at trace
levels, evidenced by the high-temperature SO
2
(m/z 64) peak
seen at ~960ºC. SO
2
release also occurred at the same
temperature as carbonate decomposition, suggesting that a
sulfate mineral was trapped in the carbonate mineral matrix.
At temperatures of ~350-600ºC, we observed a large m/z 32
peak, derived from a combination of
32
S from SO
2
and O
2
released from multiple sources, including CO
2
, SO
2
, H
2
O, and
possibly oxides. The peaks at m/z 28 primarily indicate CO
associated with degradation of carbonate minerals and
oxidation of organic compounds, but a small percentage may
represent N
2
. The high-temperature m/z 28 peak that is
observed in both sample 0212 and the procedural blank is
believed to derive from N
2
and/or CO outgassing from the
alumina crucible itself. To enable more accurate mineral
assignments using this instrument in the future, an EGA
library will be created from analysis data of a variety of pure
mineral standards under the same pyrolysis conditions.
Fig. 9. VAPoR evolved gas analysis of DRATS sample 0212, a vesicular
basalt collected at Black Point Lava Flow in Arizona, showing selected
inorganic and organic volatiles released from the sample as a function of
sample temperature.
V. T
IME OF FLIGHT MASS SPECTROMETER
To identify trace volatiles of interest with similar masses
(e.g.
3
He/HD, N
2
H
4
/O
2
) and make isotopic measurements,
mass spectrometers with higher mass resolution and sensitivity
than our current RGA quadrupole mass spectrometer will be
required. We are currently developing a miniaturized
reflectron time of flight mass spectrometer (TOF-MS) for
VAPoR. The design of the TOF-MS component of VAPoR
has been described previously [27], but the mass spectrometer
has recently been modified with a new extended ion source
and lens assembly needed to improve instrument sensitivity.
The new TOF-MS has been systematically tested in both
linear and reflectron modes (Fig. 10). In the reflectron (ion
mirror) mode the direction of the ions is reversed in the
reflectron and the ions are measured at a detector placed close
to the ion source. The TOF-MS is mounted inside a vacuum
chamber with a base pressure of 10
-8
Torr. In parallel with the
experimental testing, electrodynamics simulations of the TOF-
MS with the new extended ion source have been conducted
using SIMION in both linear and reflectron modes.
The TOF-MS above consists of a carbon nanotube (CNT)
field emission electron gun, NiCr ion extraction, steering, and
focusing lenses, a monolithic curved-field reflectron, and two
microchannel plate (MCP) detectors (one each for linear and
reflectron modes) operated in ion counting mode (Fig. 10).
9
During operation, ions are first generated by electron
ionization within the ion source. High-speed electronics then
pulse the ion lens voltages to accelerate ionized species into
the TOF analyzer. The ions are then separated by mass and
arrive as isomass packets at the detector.
Fig. 10. The VAPoR TOF-MS shown inside a vacuum chamber at NASA
Goddard can now be operated in both linear and reflectron modes. A new
extended carbon nanotube electron gun (CNT e-gun) has recently been
integrated to the TOF-MS for improved sensitivity over the previous small
format e-gun.
By measuring MCP voltage as a function of time, a mass
spectrum is acquired. The new extended ion source has a
much larger ionization volume and ion transmission. Based
on our calculations and SIMION modeling, we estimate that
the new extended ion source will yield a sensitivity
improvement of three orders of magnitude over previous
reports using a smaller electron gun [27]. Details of the
scaled-up electron gun design will be discussed elsewhere
[Southard et al. in preparation].
The highest mass resolution performance is obtained in
the reflectron mode of the TOF-MS. The effect of the
reflectron is to lengthen the flight path for better temporal
separation and better spatial focusing of the ion packets. In
the current TOF-MS prototype, we conducted similar
optimization efforts to that described in the linear case above,
with the addition of tuning the curved field profile of the
reflectron by adjusting individual voltages along the reflectron
length. Experimentally, performance improvements have
been demonstrated in mass separation and mass resolution,
compared to the linear case above. For example, at mass 28
(N
2
/CO), the mass resolution (m/m) is 120, nearly twice the
mass resolution of the linear case which is ~ 65. We are
continuing to optimize the tuning and alignment of the TOF-
MS instrument to improve performance and achieve the mass
resolution and sensitivity requirements for the VAPoR
instrument. Our ultimate target for the VAPoR TOF-MS is to
achieve a mass resolution of ~600-1000 to enable separation
of several key volatile species of interest on the lunar surface
and improve the sensitivity of the mass spectrometer to ~ 3 x
10
-4
counts/sec/molecule/cc. The addition of a time of flight
mass spectrometer with enhanced sensitivity and improved
mass resolution compared to the current RGA on a flight
instrument should make it possible to identify some species
(e.g.,
3
He/HD) that we are currently unable to resolve with the
VAPoR field unit.
VI. C
ONCLUSION
In situ vacuum pyrolysis evolved gas measurements of the
lunar regolith and other airless bodies including asteroids are
needed to characterize and determine the origins of volatiles,
particularly, water, an important resource for future human
exploration. Using the VAPoR instrument during NASA's
2011 Desert RATS field campaign, we successfully
demonstrated that high temperature vacuum pyrolysis of solid
samples to temperatures exceeding 1300°C coupled with line
of sight detection of volatiles by mass spectrometry can be
used for the identification of resources including water and
oxygen in surface samples. The inclusion of evolved gas
analysis capability in the field and continued testing of
instruments such as VAPoR in future field tests will be critical
to the success of future robotic and human planetary resource
exploration missions. The development of sample collection
protocols designed to minimize or eliminate contamination
from analyses such as those conducted by VAPoR are critical
considerations for future space exploration architecture
planning.
A
CKNOWLEDGMENTS
The authors would like to acknowledge support from the
NASA Astrobiology Science and Technology Instrument
Development Program (07-ASTID07-0020), the NASA Moon
and Mars Analog Mission Activities Program (10-
MMAMA10-0001), and the NASA Goddard Space Flight
Center Internal Research and Development Program. We also
thank B. A. Janoiko for logistical support in the field and J.
Farmer and C. Evans for assistance with the sample collection
and allocation protocol for VAPoR.
R
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BIOGRAPHIES
Daniel Glavin received a B.S. in
Physics from the University of
California, San Diego in 1996 and a
Ph.D. in Earth Sciences from the
Scripps Institution of Oceanography in
2001. He has been with NASA's
Goddard Space Flight Center for the
past 8 years where he is involved in
instrument development for Astrobiology missions. He is
the Planetary Protection lead for the Sample Analysis at
Mars (SAM) instrument suite on the Mars Science
Laboratory (MSL) and is leading the development of the
VAPoR pyrolysis mass spectrometer instrument designed to
detect volatiles released from rock samples on the Moon.
Inge ten Kate received a M.S. in
Aerospace Engineering from Delft
University of Technology in 1999 and a
Ph.D. in Astronomy from Leiden
University in 2006, both in the
Netherlands. From 2006-2011 she
worked at NASA Goddard Space Flight
Center where she was involved in the
development of several instruments including as Co-
Investigator of the VAPoR instrument described here. She
currently works as visiting scientist at the Centre for Physics
of Geological Processes at the University of Oslo, Norway.
Her research interests include degradation and preservation
of organic material, with a current focus on Mars.
Stephanie Getty is a Spectrometer
Instrumentation Engineer at NASA
Goddard Space Flight Center,
emphasizing the development of
advanced scientific instrument
technologies for space. Her current
research interests include
carbonaceous field emission materials for electron impact
ionization mass spectrometry, detection of astrobiologically
relevant organic molecules by advanced analytical and
ionization techniques for planetary mass spectrometers, and
the use of carbon nanotubes as new stray-light suppression
coatings for space-based observatories. She received her
Ph.D. in Physics from the University of Florida in 2001 and
held a Director of Central Intelligence Postdoctoral
Fellowship in the Physics Department at the University of
Maryland, College Park, prior to joining NASA Goddard
Space Flight Center in 2004.
Adrian Southard received his bachelor
of arts in physics from New College of
Florida in 2000 and his Ph.D. in
chemical physics from University of
Maryland in 2009. His Ph.D. research
focused on transport in organic
semiconductors and novel device
fabrication methods. He joined the VAPoR team at NASA
Goddard about 2 years ago to work on development of its
Time Of Flight Mass Spectrometer.
11
Heather Franz is a Research Analyst
with the Planetary Environments
Laboratory at NASA's Goddard Space
Flight Center. She is currently a Ph.D.
candidate in Geology at the University
of Maryland, specializing in Martian
sulfur isotope geochemistry. She also holds an M.S. in
Applied Physics from The Johns Hopkins University and a
B.S. in Aerospace Engineering from the University of
Maryland. She has been a member of the science team for
the SAM instrument for 6 years, using the prototype system
to develop experimental protocols for the MSL operations
phase. Prior to joining the SAM team, she worked briefly as
a flight controller for the Earth Radiation Budget Satellite
before enjoying 14 years designing trajectories for
spacecraft in a variety of orbital regimes at GSFC's Flight
Dynamics Facility.
Steven Feng received a B.S. in
Electrical Engineering from the
University of Maryland, College Park
in 1989 and a M.S. in Electrical
Engineering from John Hopkins
University in 1995. He has been NASA
Goddard Space Flight Center for 21 years where he is
involved in instrument electronics development for
numerous space flight mass spectrometers in planetary
missions, such as Cassini-Huygens INMS and GCMS,
Nozomi NMS, Contour NGIMS, and MSL-SAM QMS.
Jason Dworkin began research into the
origins of life at the University of
Houston, where he studied amino acids
and co-enzymes. He received an A.B. in
Biochemistry from Occidental College
in 1991 and completed his Ph.D.
in biochemistry at the University of
California, San Diego in 1997, where he
investigated pre-RNA nucleobases. He then carried out
postdoctoral research at NASA Ames on astrophysical ices
until 2002 when he founded the Astrobiology Analytical
research group at NASA Goddard Space Flight Center to
study extraterrestrial organics. He is currently Chief of the
Astrochemistry Branch at NASA Goddard and Project
Scientist for the OSIRIS-REx mission.
Jacob Bleacher has been a research
scientist at NASA’s Goddard Space
Flight Center in the Planetary
Geodynamics Lab since 2006. His
research focuses on the development and
modification of planetary volcanic
terrains through a combination of
terrestrial field studies and spacecraft data analysis. He
combines his expertise in field and planetary geology to help
build and test the science capabilities of NASA’s newest
instrument, suit and rover technologies and has served as a
Desert Research And Technology Studies crewmember since
2009. He holds a B.A. in Geosciences from Franklin &
Marshall College and a Ph.D. in Geological Sciences from
the Arizona State University.
... For all parameter combinations, the partial pressures as well as the total gas pressure show a very similar trend at temperatures above 300 C. It is assumed that outgassing is caused by volatiles released from mineral decomposition rather than from surface desorption. Similar conclusions were drawn by Street et al. (2010), ten Kate et al. (2010), and Glavin et al. (2012), who measured a release of CO 2 , SO 2 , H 2 S, and S between 300 C and 600 C. Table 2 lists the major mineral abundances of NU-LHT-2M for particles with a single phase (99.2% of all particle compositions are a single phase). According to Street et al. (2010) the source material of NU-LHT-2M has undergone hydrothermal alteration, which could explain the release of trapped H 2 O at higher temperatures. ...
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