Mud volcanoes provide a unique low-temperature window into the Earth s subsurface - including the deep biosphere - and may prove to be significant sources of atmospheric methane. The identification of analogous features on Mars would provide an important new class of sites for geological and astrobiological exploration. We report new work suggesting that features in Acidalia Planitia are most consistent with their being mud volcanoes

Allen, C.C.

Baker, D.M.

Oehler, D.Z.

NASA Technical Reports Server

MUD VOLCANOES - A NEW CLASS OF SITES FOR GEOLOGICAL AND ASTROBIOLOGICAL
EXPLORATION OF MARS. C.C. Allen 1 , D.Z. Oehler 1 , and D.M. Baker2 1NASA Johnson Space Center,
Houston, TX 77058 carlton.c.allen@nasa.gov , dorothy.z.oehler@nasa.gov 2Brown University, Providence,
RI 02912 david_baker@brown.edu
Introduction: Mud volcanoes provide a unique
low-temperature window into the Earth’s subsurface –
including the deep biosphere – and may prove to be
significant sources of atmospheric methane. The iden-
tification of analogous features on Mars would provide
an important new class of sites for geological and as-
trobiological exploration. We report new work sug-
gesting that features in Acidalia Planitia are most con-
sistent with their being mud volcanoes.
Previous Research: Terrestrial mud volcanoes are
low shields or domes, meters to over one kilometer in
diameter, composed of mud and rock. They have been
documented at over 40 sites onshore and over 20 sub-
sea locations [1]. The largest concentration of mud
volcanoes is in Azerbaijan and the adjacent Caspian
Sea. Mud volcanoes are formed when overpressured
gases and liquids from as deep as several kilometers
breach the surface, carrying slurries of fluid, mud, and
rocks [2]. These conditions often occur in regions of
rapid sedimentation and hydrocarbon generation, and
many mud volcanoes emit copious quantities of vola-
tiles, primarily water and methane.
Mud volcanoes have been cited as possible analogs
to martian features from a wide range of locations.
These include the dichotomy boundary regions near
Isidis [3] and Utopia [4], the Borealis “back basin” [5],
and Chryse Planitia [6,7]. Farrand et al. [8] hypothe-
sized that numerous domes and cones in Acidalia are
either mud volcanoes or spring mounds. We have re-
examined these features, using the full range of data-
sets now available from Mars orbit.
Acidalia: Domes and cones, hundreds of meters to
kilometers in diameter, are scattered across much of
Acidalia Planitia. These features overlie the Vastitas
Borealis plains, mapped as Hesperian to Amazonian
sedimentary units of basaltic composition [9,10].
Farrand et al. [8] based their analysis on images
from the MOC (Mars Orbiter Camera; 1.5 to 12
m/pixel) and THEMIS (Thermal Emission Imaging
System; 19 m/pixel visible; 100 m/pixel infrared) in-
struments. We conducted high-resolution morphologic
and spectral analysis of specific Acidalia features em-
ploying HiRISE (High Resolution Imaging Science
Experiment; 0.3 m/pixel) panchromatic and color im-
ages, as well as multi-spectral images and point spectra
obtained by the CRISM (Compact Reconnaissance
Imaging Spectrometer for Mars; 16 to 20 m/pixel;
0.362 to 3.920 jtm spectral range) instrument.
Farrand et al. [8] reported that the domes and cones
appear darker than the adjacent plains in THEMIS
nighttime infrared images. This observation demon-
strates that the domes and cones are composed of ma-
terial with lower thermal inertia than the plains.
HiRISE images show isolated and overlapping
high-albedo domes and cones, many with central de-
pressions. The centers (inferred high points) of the
features often show concentric layering, while the out-
er portions are finely furrowed and generally rock-free
at sub-meter resolution (Fig. 1). The dome material
clearly overlies the plains. Meter-scale texture charac-
teristic of the underlying plains is locally detectable at
the margins of the domes, indicating that this material
can thin to a feather edge. Impact craters that pierce
several domes indicate that the bright material is irre-
gularly layered and tens of meters thick. Small dunes
of bright material, possibly eroded from the domes, are
observable within nearby troughs.
r /
h	 , ,
1
• ." .(;-/;-'	 ..
•:	 ;
•
Figure 1. High-albedo dome in Acidalia Planitia
(HiRISE image PSP_008522_2210 IRB).
A CRISM image (3837 vnir_fem browse product;
11] demonstrates that the Acidalia domes and plains
have distinct and consistent spectral signatures. The
plains in this image appear blue, indicating the pres-
ence of olivine and / or pyroxene. The domes appear
green, indicating coatings on rocks or ferric oxides.
https://ntrs.nasa.gov/search.jsp?R=20090010218 2019-08-30T06:26:58+00:00Z
The CRISM spectra of individual domes, with cor-
rections for the martian atmosphere and dust, were
ratioed to spectra representative of the adjacent plains
(Leah Roach, Brown Univ.; Fig. 2). The visible (VIS)
portion of the ratio shows a steep shoulder near 0.6
jtm, indicative of ferric iron. The near-infrared (NIR)
portion of the ratio shows positive features in the same
positions as the negative features in spectra of high-
calcium pyroxene. These imply that the dome spec-
trum is essentially flat in the NIR, and that the ratio is
showing the inverse signatures of pyroxene in the
plains material. The ratio spectrum shows no features
corresponding to precipitates or evaporite minerals.
Figure 2. CRISM 3837 ratio spectrum (dome / plains
material).
These observations, in combination, argue against a
number of possible origins for the Acidalia domes in-
cluding impact, volcanic eruption, or deposition from
springs. Impact craters of similar scale exhibit deeper
depressions and blockier ejecta blankets than the
domes. The dome materials have lower thermal inertia
than the plains, as well as featureless NIR spectra, in-
dicating that the domes are not composed of basalt.
The lack of spectral signatures for evaporites and pre-
cipitates argues against a spring mound origin.
Conversely, the observations are consistent with
mud volcanoes. Dried mud has lower thermal inertia
than rock, and is likely friable enough to be smoothed
by wind erosion. The lack of specific mineral signa-
tures in the VIS and NIR spectra is consistent with
amorphous or poorly-crystalline materials like those
found in clay-rich mud. The ferric iron signature indi-
cates that dome material is more oxidized than plains
material, suggesting an origin associated with water.
This is consistent with conclusions by Wyatt [10] that
aqueous alteration occurred in Acidalia Planitia. It is
also consistent with regional assessment by Oehler and
Allen [7] that the Chryse-Acidalia area is a prime can-
didate for having developed extensive mud volcanism.
Implications for Astrobiology: If the Acidalia
domes or similar features elsewhere on Mars have an
origin similar to that of terrestrial mud volcanoes, then
these martian features are potentially important sites
for martian geology and astrobiology. Mud volcanoes
bring material from depth to the surface at tempera-
tures well below those associated with impact cratering
or volcanism. On Earth some mud volcanoes sample
deep sedimentary strata, carrying physical and chemi-
cal biosignatures to the surface. While the depth
sampled by the martian features is unknown, seismic
and stratigraphic studies demonstrate that terrestrial
mud volcanoes sample as deep as several kilometers.
Terrestrial mud volcanoes also erupt significant
quantities of water. The Acidalia domes do not show
evidence of channeling, suggesting that large amounts
of water did not flow from their craters. The lack of
channels may also reflect this material’s susceptibility
to wind erosion. The oxidized nature of the dome ma-
terial, as witnessed by its abundance of ferric iron,
suggests that the material interacted with water at
depth. Thus, these domes may hold important clues to
the subsurface hydrosphere.
Many terrestrial mud volcanoes are located in re-
gions of abundant hydrocarbons. The Azerbaijan and
Caspian features are closely associated with major oil
and gas fields. Mud volcanoes are known to erupt
large amounts of methane derived from subsurface
hydrocarbons [1]. Methane has been detected in the
martian atmosphere, where its short lifetime suggests
currently active sources [12-14]. We are exploring the
possibility that a portion of this methane may derive
from the martian equivalents of mud volcanoes.
References: [1] Milkov A.V. (2003) AAPG Ann.
Mtg. Abs. [2] Kvenvolden K.A. & Rogers B.W.
(2005) Marine Petrol. Geol. 22, 579-590. [3] Tanaka
K.L. et al. (2000) LPS XXXI, Abs. #2023. [4] Skinner
J.A. & Tanaka K.L. (2007) Icarus 186, 41-59. [5] Kite
E.S. et al. (2007) AGU Fall Mtg. Abs. [6] Rodriguez
J.A.P. et al. (2007) Icarus 191, 545-567. [7] Oehler
D.Z. & Allen, C.C. (2009) LPS XL, Abs. #1034. [8]
Farrand W.H. et al. (2005) JGR 110, E05005:1-14. [9]
Tanaka K.L. et al. (2005) USGS Sci. Invest. Map 2888.
[10] Wyatt M.B. (2008) GSA Ann. Mtg. Abs. #268-3.
[11] Pelkey S.M. et al. (2007) JGR 112, EO8S14,
doi: 10:1029. [12] Krasnopolsky A. et al. (2004) Ica-
rus 172, 537-547. [13] Mumma M.J. et al. (2004) 36th
DPS, Abs. #26.02. [14] Formisano V. et al. (2004)
Science 306, 1758-1761.


Mud Volcanoes - A New Class of Sites for Geological and Astrobiological Exploration of Mars

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