Hope for present-day Martian groundwater dries up

Date:
January 24, 2022
Source:
University of Texas at Austin
Summary:
Liquid water previously detected under Mars' ice-covered south
pole is probably just a dusty mirage, according to a new study of
the red planet.

The finding challenges a 2018 study that appeared to find liquid
water under Mars' south polar cap.



FULL STORY ========================================================================== Liquid water previously detected under Mars' ice-covered south pole is
probably just a dusty mirage, according to a new study of the red planet
led by researchers at The University of Texas at Austin.


========================================================================== Scientists in 2018 had thought they were looking at liquid water when
they saw bright radar reflections under the polar cap. However, the
new study published Jan. 24 in the journal Geophysical Research Letters
found that the reflections matched those of volcanic plains found all
over the red planet's surface.

The researchers think their conclusion -- volcanic rock buried under
ice -- is a more plausible explanation for the 2018 discovery, which was already in question after scientists calculated the unlikely conditions
needed to keep water in a liquid state at Mars' cold, arid south pole.

"For water to be sustained this close to the surface, you need both
a very salty environment and a strong, locally generated heat source,
but that doesn't match what we know of this region," said the study's
lead author, Cyril Grima, a planetary scientist at the University of
Texas Institute for Geophysics (UTIG).

The south polar mirage dissolved when Grima added an imaginary global
ice sheet across a radar map of Mars. The imaginary ice showed how Mars' terrains would appear when looked at through a mile of ice, allowing
scientists to compare features across the entire planet with those under
the polar cap.

Grima noticed bright reflections, just like those seen in the south pole
but scattered across all latitudes. In as many as could be confirmed,
they matched the location of volcanic plains.



==========================================================================
On Earth, iron-rich lava flows can leave behind rocks that reflect radar
in a similar way. Other possibilities include mineral deposits in dried riverbeds.

Either way, Grima said, figuring out what they are could answer important questions about Mars' history.

Although there may not be liquid water trapped under the southern polar
cap, there is plenty of water ice on Mars, including in the thick polar
caps. In fact, the new study hints at Mars' wetter past.

Isaac Smith, a Mars geophysicist at York University, believes the bright
radar signatures are a kind of clay made when rock erodes in water. In
2021, Smith, who was not part of either study, found that Earth-based
clays reflected radar brightly, just like the bright spots in the 2018
south pole study.

"I think the beauty of Grima's finding is that while it knocks down the
idea there might be liquid water under the planet's south pole today, it
also gives us really precise places to go look for evidence of ancient
lakes and riverbeds and test hypotheses about the wider drying out of
Mars' climate over billions of years," he said.

Grima's map is based on three years of data from MARSIS, a radar
instrument launched in 2005 aboard the European Space Agency's Mars
Express that has accumulated tremendous amounts of information about
Mars. Grima and co-author Je're'mie Mouginot, a research scientist at
the Institute of Environmental Geosciences in Grenoble, France, plan to
dig further into the data to see what else MARSIS can turn up about Mars.

For Smith, the study is a sobering lesson on the scientific process that
is as relevant to Earth as it is to Mars.

"Science isn't foolproof on the first try," said Smith, who is an alumnus
of the Jackson School of Geosciences at UT Austin. "That's especially
true in planetary science where we're looking at places no one's ever
visited and relying on instruments that sense everything remotely."
Grima and Smith are now working on proposed missions to find water on
Mars with radar, both as a resource for future human landing sites and
to search for signs of past life.

The current study was partially funded by NASA and CNES, the French
national space agency. The Institute of Environmental Geosciences
(Institut des Ge'osciences de l'Environnement) is a joint research
unit of the French National Centre for Scientific Research, Universite' Grenoble Alpes and other institutions in France. UTIG is a research unit
of the UT Jackson School of Geosciences.

========================================================================== Story Source: Materials provided by University_of_Texas_at_Austin. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* A_view_of_Mars'_south_pole ========================================================================== Journal Reference:
1. C. Grima, J. Mouginot, W. Kofman, A. He'rique, P. Beck. The Basal
Detectability of an Ice‐Covered Mars by MARSIS. Geophysical
Research Letters, 2022; 49 (2) DOI: 10.1029/2021GL096518 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220124090503.htm

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