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THEMIS observes possible cave skylights on Mars


Abstract and Figures

1] Seven possible skylight entrances into Martian caves were observed on and around the flanks of Arsia Mons by the Mars Odyssey Thermal Emission Imaging System (THEMIS). Distinct from impact craters, collapse pits or any other surface feature on Mars, these candidates appear to be deep dark holes at visible wavelengths while infrared observations show their thermal behaviors to be consistent with subsurface materials. Diameters range from 100 m to 225 m, and derived minimum depths range between 68 m and 130 m. Most candidates seem directly related to pit-craters, and may have formed in a similar manner with overhanging ceilings that remain intact.
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THEMIS observes possible cave skylights on Mars
G. E. Cushing,
T. N. Titus,
J. J. Wynne,
and P. R. Christensen
Received 16 May 2007; revised 23 July 2007; accepted 14 August 2007; published 15 September 2007.
[1] Seven possible skylight entrances into Martian caves
were observed on and around the flanks of Arsia Mons by
the Mars Odyssey Thermal Emission Imaging System
(THEMIS). Distinct from impact craters, collapse pits or
any other surface feature on Mars, these candidates appear
to be deep dark holes at visible wavelengths while infrared
observations show their thermal behaviors to be consistent
with subsurface materials. Diameters range from 100 m to
225 m, and derived minimum depths range between 68 m
and 130 m. Most candidates seem directly related to pit-
craters, and may have formed in a similar manner with
overhanging ceilings that remain intact. Citation: Cushing,
G. E., T. N. Titus, J. J. Wynne, and P. R. Christensen (2007),
THEMIS observes possible cave skylights on Mars, Geophys. Res.
Lett.,34, L17201, doi:10.1029/2007GL030709.
1. Introduction
[2] The existence, physical properties and possible bene-
fits of extraterrestrial caves have been a subject of scientific
discussion for as long as spacecraft have observed planetary
surfaces. Oberbeck et al. [1969] compared lunar and ter-
restrial lava-tubes, and Carr et al. [1977] examined similar
structures on Mars. Horz [1985] suggested using lunar lava
tubes as shelters for human habitation, and Boston et al.
[2004] discussed the same for Mars along with favorable
implications for astrobiology. Even now, engineers are
developing technologies to allow both human and robotic
missions to physically explore extraterrestrial caves [Boston
et al., 2004; Boston and Dubowsky, 2005]. Unfortunately,
cave detection by spacecraft is difficult because their instru-
ments have limited resolution and generally point nadir
(straight downward), requiring detectable cave entrances to
face skyward and be large enough to be resolved from orbit.
[3] The Martian surface experiences a range of signifi-
cant hazards. Micrometeoroids, solar flares, UV radiation,
high-energy particles from space and intense dust storms
regularly bombard the surface [Mazur et al., 1978; Kuhn
and Atreya, 1979; Frederick et al., 2000; Boston et al.,
2004; Schulze-Makuch et al., 2005], where absolute temper-
atures can double over a single diurnal cycle [Cushing et al.,
2005]. Caves may be among the only structures on Mars
that offer long-term protection from such hazards.
[4] We have identified seven candidate cave entrances
(skylights) located on or near the flanks of Arsia Mons
(southernmost of the three massive shield volcanoes of
Tharsis Montes, Figure 1). This region has widespread pit
craters and grabens, suggesting an abundance of subsurface
void spaces [Ferrill et al., 2003; Wyrick et al., 2004]. These
candidates may have formed in a manner comparable to pit
craters (which are usually found nearby) except that an area
of competent surface materials may have remained intact to
form a ceiling as subsurface materials collapsed and drained
into the subterranean voids below (see Figure 2 and auxil-
iary material).
These candidate skylights appear to descend
100 meters or more beneath the surface and may either
(1) open laterally into cavernous spaces; (2) plunge deeply
into subsurface faults; or (3) may not be caves at all, instead
being deep cylindrical shafts with sheer vertical walls. With
currently available data, we cannot determine which of
these cases is correct because THEMIS only observes from
nadir and can’t see whether the candidates have vertical or
subvertical walls. In any case, these are extremely unusual
and interesting features worthy of further investigation.
2. Observations
[5] The majority of data were collected by THEMIS,
which observes the surface from nadir at both visible and
thermal-infrared wavelengths. The thermal-infrared camera
(IR) observes nine bands ranging between 6.3 15.3 mm
with a spatial resolution of 100 meters per pixel. The
visible-wavelength camera (VIS) observes at 18 or 36 m/
pixel in 5 bands, though only band-3 images (0.65 mm)
are used for this investigation. THEMIS observes with both
VIS and IR cameras late in the afternoon (1500 1700 hrs,
when the sun has past transit and doesn’t shine as deeply
into the candidates). Only the IR camera is used for
predawn observations (03000500 hrs) which are nec-
essary to provide a diurnal range of thermal coverage
[Christensen et al., 2004].
[6] Cave entrances detectable by THEMIS are probably
rare because they must face skyward and have minimum
diameters of 100 m. While VIS observations can resolve
smaller features than this, they do not show sufficient detail
to verify definite cave-like characteristics. We therefore use
100-meter IR observations to confirm that each candidate
exhibits smaller amplitudes of diurnal temperature varia-
tions than the immediately surrounding terrain. This re-
quirement of minimum 100-m diameters and skyward
facing should seriously limit the number of cave entrances
detectable by THEMIS (the only thermal imaging system
currently orbiting Mars.).
GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L17201, doi:10.1029/2007GL030709, 2007
Astrogeology Team, U.S. Geological Survey, Flagstaff, Arizona, USA.
Department of Physics and Astronomy, Northern Arizona University,
Flagstaff, Arizona, USA.
Department of Biological Sciences, Northern Arizona University,
Flagstaff, Arizona, USA.
Department of Geological Sciences, Arizona State University, Tempe,
Arizona, USA.
Copyright 2007 by the American Geophysical Union.
Auxiliary materials are available in the HTML. doi:10.1029/
Figure 1. MOLA shaded relief map of Arsia Mons. Caldera floor is centered at approximately 239°E, 9°S. Locations of
the seven candidate cave skylights are labeled.
Figure 2. Seven candidate cave skylights: (a) Dena, (b) Chloe¨, (c) Wendy, (d) Annie, (e) Abby (1) and Nikki (2), and
(f) Jeanne. Arrows signify directions of solar illumination and of North. To facilitate our photoclinometry routine, each
candidate is map-projected with sunlight coming from the 9 o’clock direction.
[7] VIS images showing dark, circular features in the
midst of pit-crater chains gave our first indication of
potential skylight openings. These candidates are obviously
distinct from typical pit craters because of their lack of
sloped walls or visible floors, and they also lack the visible
characteristics (such as raised rims or ejecta patterns) that
would associate them with impact craters. Additionally,
thermal behaviors confirm these are not misidentified sur-
face features such as dark sand or rock (analysis section).
Illuminated upper-rims can be seen in several THEMIS VIS
images, and off-nadir observations from other orbiting
instruments (possibly HiRISE) will image these candidates
from the side, (and at much higher spatial resolution)
showing us the interior wall structure, and possibly provid-
ing ceiling thicknesses if such ceilings exist. Observations at
earlier times of day will allow us either to see the floors or
to constrain minimum depths to deeper values than we have
at present (analysis section). Observations of illuminated
floors will provide us with definite depth values, but will
not necessarily determine cave-like characteristics.
3. Analysis
[8] For a convenient aid in identification and visualiza-
tion, we informally identify these ‘seven sisters’ on Arsia
Mons as: Dena, Chloe¨, Wendy, Annie, Abby, Nikki and
Jeanne (Figures 1 and 2, Table 1). Diameters of these
candidates are estimated by taking an average of several
measurements using the 18 m/pixel resolution of
THEMIS VIS, and range between 100 252 meters. Only
minimum values of each candidate’s depth can be estimat-
ed because the floors are completely in shadow during
THEMIS observations. These minimum depths (d
easily constrained using observed diameters (D) and their
respective solar incidence angles (i) where d
= D/tan(i).
Our ‘useful’ incidence angles ranged between 61.5° 69.9°
and returned respective d
values between 68101 m
(Table 1), though actual depths could be considerably
greater. We also model topographic profiles across each
candidate using a 1-dimensional photoclinometry (shape
from shading) routine described in the auxiliary material.
[9] The Mars Orbiter Camera (MOC) observed ‘Dena’
with a partially illuminated floor earlier in the afternoon
with an incidence angle of 40.15°(1430 hrs, Figure 3b).
This valuable observation allows us to tightly constrain the
floor’s depth at the edge of the shadow to 130 m while
the THEMIS minimum depth is only 80 m.
[10] THEMIS IR shows that diurnal temperature varia-
tions are much smaller in the candidate skylights than on
any of their surrounding surfaces. In Figure 4, notice how
‘Annie’ is warmer in the afternoon than the shadows of
adjacent collapse pits, while cooler than the sunlit portions.
Nighttime temperatures, meanwhile, are warmer than all
nearby surfaces. This behavior is consistent in all seven
candidates, and would be expected of cave interiors that
Table 1. Physical Parameters of Candidate Skylights
Name Longitude Latitude Diameter Incidence Angle Minimum Depth Minimum d/D Ratio Elevation THEMIS VIS ID
Annie 240.03°E 6.52°S 225 m 65.9°101 m 0.44 11055 m V18340001
Dena 239.02°E 6.31°S 162 m 63.6°80 m 0.49 9100 m V18053001
Jeanne 241.38°E 5.57°S 165 m 65.7°75 m 0.45 9970 m V18315002
Wendy 240.32°E 7.84°S 125 m 61.5°68 m 0.54 15500 m V17716001
Chloe 239.21°E 4.29°S 252 m 83.1°N/A N/A 5700 m V13448001
Abby 240.54°E 6.713°S 100 m 84.4°N/A N/A 11150 m V14334002
Nikki 240.55°E 6.708°S 180 m 84.4°N/A N/A 11150 m V14334002
Diameter, D; depth, d. Minimum depths are not calculated for observations with very high solar incidence angles (>80°). Minimum d/D ratio is the ratio
of minimum depth to the diameter of each candidate. Small impact craters on Mars typically have d/D ratios of about 0.2.
Figure 3. (a) A THEMIS observation of Dena at 18-m resolution with an incidence angle of 63.6°and a minimum depth
of 80 m. (b) A MOC observation (R0800159) at 6-m resolution with a partially illuminated floor (40.15°incidence
angle). The depth at the edge of the shadow is 130 m.
receive little or no daily solar insolation [Howarth, 1980;
Pflitsch and Piasecki, 2003].
[11] The candidates Wendy, Dena, Annie and Jeanne
have both VIS and diurnal IR coverage, and are large
enough to give distinct IR signatures at 100-m resolution.
Chloe¨ , Abby and Nikki have the same visible and thermal
characteristics as the others, and are also strong candidates,
but their minimum depths could not be constrained to useful
values because they were observed late in the afternoon
when sunlight comes from the side and doesn’t shine deeply
into them (observed incidence angles >83°).
4. Formation Mechanisms
[12] Most of the candidates are either adjacent to pit
craters, or are directly in-line with pit-crater chains, suggest-
ing similar formation processes, though pit craters consis-
tently show distinct walls that slope inward at the angle of
repose (30°). Recent investigations and some terrestrial
analogues suggest these pits are likely caused by the
drainage of loosely consolidated surface materials into deep
extensional fractures or faults that could reach down to 5 km
into the crust [Ferrill et al., 2003; Wyrick et al., 2004].
[13] Some terrestrial pit craters found in Hawaii are
visibly similar to our candidates [Okubo and Martel,
1998]. These form in young basalt with walls that collapse
inward over short geologic timescales. If these Hawaiian pit
craters are truly analogous to the candidates discussed here,
then seismic activity could possibly be an ongoing process
on Arsia Mons at the present time. It’s also possible that
these candidates are much older and fairly stable, and might
be a halted intermediate stage in pit-crater formation. In
either case, some of these Hawaiian pits such as ‘Devil’s
Throat’ [Okubo and Martel, 1998] may still be excellent
terrestrial analogues (the Hawaiian pits do not open into
cavernous spaces, but have been observed to crosscut lava
tubes). Some suggested causes for Martian pit-crater chains
include dike intrusion [e.g., Wilson and Head, 2002; Scott et
al., 2002], and collapsed magma chambers [Mege et al.,
2000]. See Wyrick et al. [2004] for a more detailed expla-
nation of possible pit-crater formation mechanisms. Regard-
less of the mechanism, there is general consensus that
subsurface void spaces with sufficient volume are necessary
to accommodate the immense volume of collapsed materi-
als, which may be up to tens of km
for a single pit [Wyrick
et al., 2004].
[14] Because Annie and Dena lie directly along the
centerline of pit-crater chains (and Abby, Nikki and Wendy
are immediately adjacent to similar chains), we propose
these candidates may have formed through a similar process
of collapse that has either halted or is still in progress. Local
topography indicates a possibility that these candidates have
intact ceilings above laterally extending cavernous spaces,
or may extend deeply into subsurface voids that have not
been completely filled by the collapsed materials. Chloe¨ and
Jeanne are unique from the other candidates because they
have no nearby collapse features to indicate a local presence
of subsurface void spaces. This could indicate a different
formation mechanism, but otherwise, their sizes, appearan-
ces and thermal behaviors are identical to the other candi-
dates. These two skylights may still open into subsurface
voids although local topography does not indicate such
spaces. Many cave skylights on Earth expose subsurface
voids such as lava tubes or sink-holes that are not otherwise
discernible by local terrain features [Calvari and Pinkerton,
1999; Miyamoto et al., 2005].
5. Conclusion
[15] Appearances and thermal behaviors of all seven
candidates are consistent with those we should expect from
skylight openings into subsurface cavernous spaces, and the
terrain surrounding most of the candidates indicates a likely
presence of subsurface voids. There is much more to be
learned about these features and future observations will
look into these candidates at different angles, different
wavelengths, higher resolutions and at different times of
day which may show internal structures and possibly
provide more clues about how they formed and why they
[16] As exploration targets, these candidates are too small
and too high in elevation (>5.7 km) to reach with our
current landing technologies. Astrobiological possibilities
may also be poor at these locations because if microbial life
ever did flourish on Mars, it may not have migrated to these
elevations. Furthermore, if these candidates happen to be
Figure 4. THEMIS VIS and IR images show diurnal thermal behavior of the candidate ‘Annie’. (left) The visible image,
(middle) an afternoon IR image observed concurrently with the VIS (1500 hrs), and (right) an early-morning observation
at 0400 hrs. This example shows the thermal behavior typical of all seven candidates.
cylindrical shafts without protective overhanging ceilings,
then microbial life would probably not survive due to direct
exposure to sunlight during those seasons and times of day
when the sun is directly overhead.
[17] Evidence of past fluvial activity has been docu-
mented in the Tharsis Montes region [Mouginis-Mark and
Christensen, 2005; Basilevsky et al., 2006], and water-ice
clouds are observed nearly every day of the year around
Arsia Mons [Benson et al., 2003]. Accordingly, further
research and modeling could give valuable insights about
whether these clouds affect conditions at the surface (or in
the candidate skylights). Additionally, possible evidence of
liquid water reaching the surface was recently identified in
Centauri Montes by Malin et al. [2006]. If this is true, then
caves found at lower elevations (probably below 0 km)
could hold some of this moisture, providing a potential
resource for future explorers and improving the possibility
of finding past or present microbial life.
[18] The discovery of potential skylight openings into
Martian caves is an exciting step towards exploration and
discovery. Future observations will provide more detailed
information and inspire deeper insights about the character-
istics and history of these features. A detailed search
covering other volcanic regions across Mars is currently
underway for similar targets—especially for those at lower
elevations which are easier to reach and have a greater
potential for holding some form of water and/or life. This
discovery challenges us with fresh insights and new possi-
bilities for the future of Mars exploration.
[19]Acknowledgments. This article was significantly improved by
insights given by Peter Mouginis-Mark, and from Windy Jaeger and Lazlo
Kesthelyi. Valuable ideas were also gained through conversations with
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P. R. Christensen, Department of Geological Sciences, Arizona State
University, P.O. Box 876305, Tempe, AZ 85287-1404, USA.
G. E. Cushing andT. N. Titus, Astrogeology Team, U.S. Geological Survey,
2255 N. Gemini Drive, Flagstaff, AZ 86001, USA. (
J. J. Wynne, Department of Biological Sciences, Northern Arizona
University, P.O. Box 5640, Flagstaff, AZ 86011, USA.
... 100-225 m diameters, 68-130 m minimum depths. These prospective skylights may (1) open laterally into cavernous spaces, (2) descend deeply into underground faults, or (3) not cave at all but instead be deep cylindrical shafts with steep vertical walls (Cushing et al. 2007; Viúdez-Moreiras 2021). These minimal depths (dmin) are readily determined using measured diameters (D) and sunlight incidence angles (i), where dmin = D/tan (i). ...
... These minimal depths (dmin) are readily determined using measured diameters (D) and sunlight incidence angles (i), where dmin = D/tan (i). however, actual depths may be significantly larger (Cushing et al. 2007). Shielding relies on void geometry D and depth d. ...
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Research Proposal
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The uncovering of the actual cave of the Seven Sleepers tale through several scientific domains and a new method of Quran interpretation will result in a paradigm shift. We suggest that the Dog Cave near Naples, Italy is the actual cave for this tale. Moreover, the tale occurred in the period of the emperor Vespasian in 71 A.D., and the Seven Sleepers awoke in 380 A.D., the years of the confession of faith of the emperor' Theodosius I. We argue that the new approach will allow us to decode numerous mysteries and contribute to uncovering evidence in many scientific fields, including history, physics, cosmology, and geology. This study examines a heuristic approach to unraveling the tale of the Seven Sleepers. Associating what is stated in the legend with the historical record is critical, and uncovering the evidence that might give the idea of time travel and how this evidence could be formed via a new method of Qur'an interpretation is crucial. Also, attempt to figure out who the Seven Sleepers are. Because the restrictions of specific sources limited previous research of the Seven Sleepers narrative, the outcome was toward a definite place, emperor identity, and date of the tale's occurrence, despite the interest in uncovering the Quran's secret. A few scholars attempt to think outside the box to link Quranic results with scientific fields that consider the preliminary meaning of the word Quran. Furthermore, there are restrictions on the Arabic language rules. Introduction Revealing the actual cave of the Seven Sleepers will be an underground revolution for much of the evidence that is uncovered in the cave in many domains of physics, cosmology, and geology. In addition, it helps explain many concerns that have been lingering about hazy parts of history that have been attributed to myth and legend. For example, the Seven Sleepers have traditionally been seen by researchers in the scientific community as a myth concocted by the ancient people's creative minds. In the period from the 9th to the 13th-century, over 200 manuscripts study the legend of the seven sleepers. Previous work has only focused on the study of the legend's origin. The legend address historical records by identifying the period of two Roman emperors, Decius 251 AD to Theodosius II 448 AD(Archer 2016; Grysa 2015). Our knowledge of the tale of the seven sleepers is mainly based on some information. The research aimed to present a new approach, revealing the cave of the seven sleepers based on literature and linking it with information extracted from the Quran using a new interpretation process. Giving new light on the foggy history of that time and uncovering the evidence that compelled them to travel ahead in time and hypothesize how it formed. In this research, we shall refer to the Seven Sleepers as "tales" rather than "legends." This investigation will be divided into five main sections. The first section summarizes the study's purpose, contribution, and literature review. In the second section, we propose a new method for Quranic interpretation of the cave chapter relating to the tale of the seven sleepers. The third section will outline the advantages of our interpretation procedure and provide the results. The fourth segment emphasizes noteworthy findings. Finally, the last section contains our conclusion.
... Terrestrial planets elsewhere in the Solar System are known to contain similar pit craters features associated with basaltic lava flows. These pit craters have been located on the lunar surface (Greeley, 1971a;Haruyama et al., 2009;Kaku et al., 2017;Sauro et al., 2020), as well as on the surface of Mars Crown et al., 2019;Cushing et al., 2007;Sauro et al., 2020;Zhao et al., 2017). In some cases on the Moon these pits are indicative of more extensive subsurface void spaces that are interpreted as lava tubes based upon corroborating geophysical gravity and radar sounding observations Kaku et al., 2017). ...
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Lava tubes are a commonplace feature on the terrestrial planets, and knowledge of tube size and location informs lava flow processes. Future exploration of lava tubes on the Moon can provide access to geologic environments that likely remain unaltered from their emplacement billions of years ago. Lunar lava tubes may also provide astronauts protection from thermal extremes, meteoroid impacts, and radiation. High‐resolution magnetic identification and characterization of lava tubes can be used to help inform future scientific investigations of lava tubes for human exploration and utilization. We demonstrate how magnetometry is useful for determining the geometry and extent of lava tubes on the Earth and, by proxy, the Moon, by relating the magnetic anomalies produced by lava tubes to their location and geomorphology. Using a proton‐precession total field magnetometer, we surveyed an area of more than 100,000 m², with cross‐tube linear traverses spaced at 3–5 m, perpendicular to an approximately 1,000 m length of the Modoc Crater lava tube complex, within the Lava Beds National Monument (California, USA). The observed magnetic anomalies of the sections known as Incline, Skull, and Ship Caves are compared against synthetic predictions, and the sensitivity of the magnetic anomalies to the tube geometry used to derive a basic relationship between the two. We use our model of terrestrial lava tube magnetic anomalies and adjust for the lunar magnetic environment to predict the signature of anomalies resulting from tubes on the Moon.
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Plain Language Summary Future Mars explorers will face a hostile environment that includes high radiation, extreme temperatures, and high windstorms. Establishing safe living quarters for prolonged stays presents problems like those of early man on Earth. The choices are whether to bring a suitable structure; to build a structure; or to find and adapt underground facilities. Of these choices, finding natural shelters requires less transported materials and less expenditure of energy than surface shelters. Lava tunnels may be useful, but future explorers will require safe quarters in the areas of Mars where sedimentary rocks are common, which will be important exploration targets to determine the geologic history of Mars. Caves in sediments on Mars may be difficult to find, but alcoves may be present. Unlike caves, alcoves have large openings at the surface in rock escarpments. Early humans used alcoves as natural shelters. Even as construction techniques developed, structures were placed within alcoves for additional protection. The Mesa Verde alcoves and pueblos in Colorado are examples of the adaptation of terrestrial alcoves for protected sites. Similarly, future astronauts to Mars could adapt shelters within alcoves as bases for operation. The earliest shelter could be as simple as a sealed tent containing a suitable atmosphere and pressure erected in an alcove.
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Lunar pits are small (∼10–300 m wide) collapse features with vertical walls and sometimes overhangs. We have identified almost 300 pits, mostly in ponds of cooled impact melt inside large craters younger than ∼1 billion years. Several of these pits may provide access to lava tubes or other caves, and those in the maria expose the layering record of the top 20–100 m of basaltic lava flows. We investigated the 21 known pits outside of impact melt ponds to determine possible origins, ages, and present‐day access to the lunar subsurface. We used Lunar Reconnaissance Orbiter Narrow Angle Camera images (<2 m per pixel) to produce detailed 3D reconstructions of six pit interiors. We evaluated the general morphology and geologic context of all twenty‐one. While four pits have contexts suggestive of lava tubes, the majority are ambiguous, although all occur in or near the maria. We also propose that pit formation is an ongoing process, as the degree of degradation of a pit is unrelated to the age of the host terrain. Much of the original volume of most pits is now filled with debris, but some exhibit significant overhangs and may have present‐day cave access. Viewing pit walls and floors, even from the rims, requires navigating steep slopes of loose material. Since the floors are also covered with rough debris piles, we recommend simple flying vehicles for initial reconnaissance.
The Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research. There are many pits on Mars, but some of them look like collapsed cave roofs. These special pits are formed by the collapse of the surface materials into the subsurface voids space. The signature of life is probable in a subsurface cave on Mars as the subsurface environment can protect life from the harsh and dangerous radiation environment of the surface. In a cave, there may be an abundance of minerals, fluids, and other key resources. Therefore, locating the access point of the subsurface cave is essential and crucial for formulating plans for robotics/human explorations of the Red Planet, Mars. We have used remote sensing data from MRO (Mars Reconnaissance Orbiter; NASA), MGS (Mars Global Surveyor; NASA), and Mars Odyssey (NASA) for identifying, mapping, and classifying selected special pit candidates on the flank of Elysium Mons, Mars. A total of thirty-two special pit candidates have been identified and classified based upon morphology and geological context. Out of these, twenty-six are newly discovered ones. The thermal behavior of twenty-three special pit candidates confirms that the special pits are radiating heat energy at nighttime, similar to potential caves. Also, cave entrances have been detected in nine candidates using the data from HiRISE camera onboard MRO. These sites could be important destinations for future robotics/human exploration and the search for life on Mars.
We show how a GIS‐based approach on 3D morphologies can be used to analyze volume variations from the microscopic scale on rock samples to large collapse pits on Earth and Mars. The microscale analyses were performed on scans acquired by a confocal laser scanning microscope from carbonate rock plates dissolved by immersion in slightly acidic solutions. Each studied sample underwent an increasing number of immersions aiming to calculate the recession rate of such stones commonly used in cultural heritage when exposed to acidic rain. We achieved this by creating a synthetic reference surface and calculating the difference in height with the scanned sample surface. The same approach was applied in planetary remote sensing to evaluate the actual volume of collapsed conduit sections of Earth and Martian lava tubes from DEMs. Lava tubes can be up to tens of kilometers long on Earth and up to hundreds of kilometers on Mars but a numerical estimate of the collapse volumes (and thus of the voids) was never attempted. The creation of a synthetic surface on top of collapses best approximating the pristine topography and calculation of the volumes in between allows comparing the total volume of the collapsed sections in distinct planetary bodies.
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The interior of a crater should have a lower mean areal density of smaller impact craters than nearby plains have, because the impacts are spread out over a larger surface area, and because the crater’s wall partially shields its interior. Inside a crater shaped like a spherical bowl (a spherical cap turned upside-down), smaller primary impact craters should be spread uniformly, but secondary craters have a more complicated distribution, usually concentrated near the center. These results may help to distinguish between populations of primary and secondary craters, and should be of interest for interpreting counts of craters within craters.
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The Mars Odyssey Thermal Emission Imaging System (THEMIS) imaged a Martian dust devil in both visible and thermal-infrared wavelengths on January 30, 2004. We believe this is the first documented infrared observation of an extraterrestrial dust devil, and the highest to be directly observed at more than 16 kilometers above the equatorial geoid of Mars. This dust devil measured over 700 meters in height and 375 meters across, and the strongest infrared signature was given by atmospheric dust absorption in the 9-micron range (THEMIS IR band 5). In addition to having formed in the extremely low-pressure environment of about 1 millibar, this dust devil is of particular interest because it was observed at 16:06 local time. This is an unusually late time of day to find dust devils on Mars, during a period when rapid surface cooling typically reduces the boundary-layer turbulence necessary to form these convective vortices. Understanding the mechanisms for dust-devil formation under such extreme circumstances will help to constrain theories of atmospheric dynamics, and of dust lifting and transport mechanisms on Mars.
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The formation of lava tubes is one of the most significant factors controlling the emplacement of lava flows. However, extents and structures of lava tubes are typically not precisely known due to the difficulty in finding lava tubes in the field. We developed a new stepped-frequency ground penetrating radar (GPR) system with shielded antennas, which allows measurements that have both high spatial resolution and large penetration depth. We performed two types of measurements over an inactive lava flow and show that this method can easily detect the existence of a lava tube. Importantly, phase reversals of the reflection signals can help identify reflections from a lava tube. Using these reflection patterns, we estimate the vertical dimension and the depth of a lava tube at Fuji volcano, which are validated by survey measurements. The presented method may be the most practical way to map terrestrial and perhaps extraterrestrial lava tubes.
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Three distinct sets of graben are associated with the volcano Alba Patera on Mars. One set, approximately circumferential to the edifice, has long been accepted to have formed as a tectonic response to an extensional stress regime associated with the evolution of the Alba Patera edifice. A second set includes mainly linear structures interpreted by many workers to have formed in response to very large-scale regional stresses. We infer that the third set of graben, all of which are relatively linear, none of which are strictly parallel to members of the second set, and many of which contain numerous pit craters, formed above long (~1000 km), laterally propagating regional dikes emanating from a volcanic center located to the south within the Tharsis region. The expected geometries of such dikes (several hundred meters depth to dike top, ~20 km depth to dike base, mean dike width ~30-90 m) are modeled on the assumption that they were fed from a shallow magma reservoir centered on a neutral buoyancy horizon, expected to be present at a depth of ~10 km on Mars. The volumes of magma in the dikes are consistent with a reservoir similar in size to those inferred to be present under the Tharsis shield volcanoes provided that the dikes were emplaced during caldera collapse episodes. The sizes of the graben associated with these dikes are consistent with the relaxation, during or immediately after dike emplacement, of preexisting regional extensional stresses of a few tens of MPa.
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Analyses of radon gas tracer measurements and observation of the variability of thermal structures have long been thought to indicate the presence of weak air currents in Niedzwiedzia (Bear) Cave, Kletno, Poland. However, only after ultrasonic anemometers were installed could different circulation systems of varying origin and the expected air movements be observed by direct measurement. This paper presents: a) the different methods applied in order to determine the weakest air currents both directly and indirectly; b) a summary of hypotheses on the subject; and c) the first results that air indeed moves in so- called static areas and that visitors affect both cave airflow and temperature. First results show that even in so-called static caves or within corresponding parts of cave systems, the term "static" has to be regarded as wrong with respect to the air currents as no situation where no air movements took place could be proven so far within the caves. Moreover, the influence of passing tourist groups on the cave climate could unequivocally be identified and demonstrated.
The deep cave zone, to which the obligatory species are restricted, is perpetually dark, nearly isothermal, has a nearly constantly saturated atmosphere possibly above the limits of most terrestrial arthropods, and usually an apparent food-limited ecosystem. I postulate that in adapting to exploit the rigorous cave environment, terrestrial troglobites have had to cope with a water surplus and have become more like aquatic organisms in their water balance mechanisms. This hypothesis is corroborated by the general observation that the drying power of the cave environment is an important parameter in understanding the distribution of terrestrial troglobites. Three main physical factors all tend to create a drier and less stable cave environment in the tropics and reduce the proportion of colonizable area in tropical caves for terrestrial troglobites. These factors are (1) tropical caves are warmer and the rate of evaporation rises almost exponentially with temperature; (2) in the tropical regions the night-time temperature usually falls below the average annual temperature, so that for tropical caves nearly every night is a winter in terms of water vapor exchange; and (3) the higher solution and erosion rates in tropical caves create more entrances, larger passages, and raised relief, allowing more air communication with the surface. These factors do not preclude the existence of terrestrial troglobites in the tropics, but caves in the tropics that meet the requirements of an adequate moisture supply and a stable environment are more difficult to find and to survey In fact, the bioclimatic model predicts that many more troglobites will be discovered as more tropical caves are surveyed and also predicts that they will be found only in cave passages that have a stable saturated or nearly saturated atmosphere.
Consideration of the effects of gravity on lithostatic stress on Mars indicates that dilational faulting found in the upper 2 km on Earth may extend to depths of 5 km on Mars.
Images obtained by the THEMIS instrument on Mars Odyssey permit the identification of many new volcanic features on Mars. Several new types of vent systems, including fissure vents within the Tharsis region, flank vents on Olympus Mons and Ascraeus Mons, and lava shields on the floor of Arsia Mons have been found. The valley networks on Hecates Tholus are seen to be more complex than previously believed. Extending from the caldera rim to the base of Hecates Tholus volcano, individual valleys change width and depth in apparent response to local topography. Valley formation spanned the time period during which lava flows from Elysium Mons embayed the southern flank of Hecates Tholus, as demonstrated by the burial of some valleys by the lava flows and the formation of sediment fans on top of adjacent parts of the flows. THEMIS images now allow new constraints to be placed on the dynamics of lava flow emplacement, with the identification of flows with well-defined lava channels on the northern flank of Ascraeus Mons, as well as an enigmatic braided lava channel. Three previously unreported collapse events (3.7 to 4.3 km in diameter) are identified within the caldera of Ascraeus Mons. Details of the mode of formation of parts of the Olympus Mons aureole can also be identified, supporting the idea that the aureole had a landslide origin. THEMIS images show that parts of the aureole have been modified by water discharged to the east of Olympus Mons.