Sky & Telescope - January 2020 - 40

Life on Mars, Reconsidered

Mars South Polar Region

Mars Express Radar Footprints

Radar Image of Subsurface

Brightest
radar echo
Permanent
ice cap

Surface
1.5 km

Brightest
radar echoes
Ice and
dust layers
Study area

Another open question is the availability of liquid water
below the surface. Orbiters have found that a frozen layer of
soil and water ice called permafrost is common in the polar
regions and covers large swaths of the rest of the planet,
including equatorial areas. But little is known about what
lies below. In July 2018, scientists using the MARSIS radar
instrument onboard the European Space Agency's orbiter
Mars Express announced they'd detected hints of liquid water
1.5 kilometers deep below the southern polar cap. While the
ﬁnding remains controversial, researchers think that these
are probably brines, bodies of water-soaked salt.
The detection would support the idea of an underground
where high pressure and milder temperatures can make liquid
water available. Although water's presence wouldn't mean life
is present, it certainly would make things easier. "Life doesn't
need a lot of water," says Amils. "Until now it was said that if
there isn't liquid water there can't be life. Well, there is water."
Obviously, the most direct way to solve these questions
is drilling, but current and future planned missions have
limited digging capabilities. The Curiosity rover can grind just
a few centimeters into the rock, and the upcoming European
ExoMars 2020 rover will be able to drill up to 2 meters down.
Insight, meanwhile, spent months stalled at a fraction of its
3-meter goal - still nowhere near where a deep biosphere
might have existed.
"Mars exploration has been focusing so much on the surface that there has been very little investment in real subsurface exploration," says Stamenkovic´, who is leading a concept
design for a solar-powered Martian drill called Ares Subsurface Great Access and Research Drill (ASGARD), able to reach
depths of at least 1 kilometer. Stamenkovic´ was recently part
of a workshop hosted by the Keck Institute for Space Studies,
where scientists and industry representatives discussed the
future of underground Martian exploration. "We've realized
that, actually, drilling technology has a lot to offer, there has
40

JANUARY 2 02 0 * SK Y & TELESCOPE

been just little investment so far," he says. "As with many
things on this planet, it's not the technology. It's the funding
that is limiting."
However, Stamenkovic´'s optimism clashes with Onstott's
experience chasing deep life. Even on Earth, he warns, drilling through frozen rock is an energy-intensive process that
is prone to equipment failures and unexpected engineering
challenges, from frozen pipes to broken drill bits.
For the time being, researchers will have to exploit other
opportunities to study the Martian subsurface until drilling technologies become available. That means relying on
indirect measurements and looking for certain features
that are far less exciting than those uncovered by drilling
kilometer-deep holes. Instead, researchers could look for
exposed crustal rocks with unusual metal or carbonate accumulations, biotextures in rocks caused by interactions with
microbes, or the buildup of organic molecules in fractures or
ﬂuid inclusions in rocks.
While the arguments for going deep in Martian exploration are sound and the possible outcomes fascinating, it
seems that we will have to put our curiosity on hold. Even
if indirect methods can reveal hints at what lies below the
surface, only specialized instruments and drilling will provide
deﬁnitive answers. Based on his experience, Onstott thinks
that humans will not reach the Martian underground until
after humans establish a base on Mars and need to access
water below the surface for a permanent colony. "That's an
important question for them," Onstott says. "When they
access the water, will there be Martian organisms in it?"

¢ Former S&T intern JAVIER BARBUZANO is a freelance writer
based in Barcelona.
Read the story of the 1977 hydrothermal vents discovery at
https://is.gd/1977ventsdisc.

ESA / N ASA / JPL / ASI / UNIV. RO ME, R. OROSEI E T A L. 2018

p SUBSURFACE LAKE? Multiple passes by the European Mars Express orbiter reveal a highly reflective layer about 1.5 km below layers of ice and
dust near Mars's south pole. Scientists suspect the 20-km-wide "anomaly" (blue triangle in radar footprints, center image) is a brine patch or lake. The
righthand panel shows an example radar profile of the region.

https://www.is.gd/1977ventsdisc

Sky & Telescope - January 2020

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