Sky and Telescope - November 2017 - 19

p EURASIAN MARS ROVER ExoMars's standout feature is its drill (tall
black cylinder), which will penetrate 2 meters beneath the surface.

EUROPE A N ROV ER: ESA / ATG MEDIA L A B; UA E IM AG ES: M OH A M MED BIN R ASHID SPACE CEN TRE

Why go to the trouble of returning samples to Earth? One
word: skepticism. A decade ago scientists probed a Martian
meteorite (ALH 84001), found in Antarctica in 1984, and
concluded that it contained microscopic fossilized evidence
of bacteria. The resulting media attention even led to a
statement from then U.S. President Bill Clinton in which
he proclaimed: "If this discovery is conﬁrmed, it will surely
be one of the most stunning insights into our universe that
science has ever uncovered." But when other teams scrutinized the results using every possible instrument and various
independent labs, they found that the Martian rock's unusual
features could all be explained without life.
"I think we'd be in the same situation, so we need to bring
those samples back and run the best possible analyses on
them," says Bell.

The ESA/Roscosmos ExoMars mission is a two-part project
to launch an orbiter and lander in 2016 and then a rover in
2020. With the ﬁrst part of the mission being less than a
stellar success (S&T: Feb. 2017, p. 10), whether the rover will
land successfully or tragically crash is an open question. But
if it does gently touch down on the Red Planet, ExoMars will
be a highly capable machine, with a raft of instruments to
rival Mars 2020's.
Like NASA's rover, it boasts cameras, infrared/visible
and Raman spectrometers, and ground-penetrating radar.
However, unfortunately bringing the deep drill means there
is simply not enough room for a cache system. "It's very difﬁcult to combine nice instruments, a large caching system,
and a deep drill," notes Vago. "We tried, but found that it is
almost impossible to do these three things on a single rover."
Hence, ExoMars will have to rely on its onboard instruments'
tests if it is to ﬁnd evidence of life.
The best chance ExoMars has of ﬁnding these biosignatures
is by detecting organics, carbon-based molecules that on Earth
are the building blocks of life. This responsibility rests on the
unique Mars Organic Molecule Analyzer (MOMA) instrument. MOMA will analyze organic molecules in much the
same way as the Viking landers or Curiosity rover. Essentially it has a number of ovens to heat up Martian dirt. Any
volatile materials will evaporate in
the heat, at which point they can be
extracted to see if they are organic.
One problem is that this technique is
plagued by perchlorates - salts
that decompose when heated
and oxidize the sample being
studied. Results from such
experiments in the past have
proven inconclusive. However,
the ExoMars team believes it has

Drilling for Life
While caching and returning samples is universally acknowledged as the best solution to quelling skepticism, many think
ancient life or its vestiges can only remain preserved deep
below the surface. Sadly, Mars 2020 doesn't carry any deep
digging tools. "The Martian atmosphere is extremely tenuous
- the pressure is roughly one hundredth that of Earth - so
radiation from the center of the galaxy and Sun penetrates
unimpeded," explains Jorge Vago, project scientist on the ESA/
Roscosmos mission to send the ExoMars 2020 rover to the
surface of Mars. "This radiation acts like a million little knives
that over millions of years cuts away the functional groups of
the molecules you are trying to study, degrading them eventually beyond the point where you can recognize them."
To solve this issue, the ExoMars rover will carry the longest
drill ever sent to the Red Planet, in order to tunnel a full
2 meters below the radiation-affected upper layers to more
pristine rocks. "We think that it's going to be a big deal in
terms of gaining access to better or more well-preserved
samples for analysis," Vago enthuses.

p EMIRATES' ENTRY The UAE's Hope orbiter (schematic above)
measures about 21/3 meters wide by 3 meters tall (7¾ by 9½ feet) and,
including fuel, will weigh about half again as much as NASA's rover. Here,
engineers discuss disassembling the craft's sun shield baffle for inspection in the lab.
s k y a n d t e l e s c o p e . c o m * N O V E M B E R 2 0 17

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Sky and Telescope - November 2017

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