As I write a new spacecraft has arrived at Mars, and its lander is preparing for its nerve-wracking descent.
ExoMars is a joint European and Russian mission. It aims to
place two landers on the surface of Mars between now and 2020, as well as
putting a new satellite in orbit. The first stage of the mission has reached
the most nerve-wracking point. The Trace Gas Orbiter (TGO) has arrived over
Mars, and the Schiaparelli lander has detached and is about to attempt to land in
the Meridiani Planum region. Another spacecraft will follow in 2020 delivering a
second lander to the red planet.
So what is this mission about and what do we hope to learn
from it?
ExoMars stands for Exobiology on Mars, so unsurprisingly one
of its key goals is to look for evidence of past or present life. To this end the
Trace Gas Qrbiter will be examining the thin martian atmosphere in far more detail
than ever before. The atmosphere of Mars is mainly composed of carbon dioxide,
with a small amount of nitrogen. However there are also very small amounts of
other “trace” gasses.
These trace gasses only make up a few parts per billion (ppb)
of the martian atmospheric composition, a fraction of a fraction of a percent.
Nonetheless they could hold a key to understanding the martian environment. Of particular
interest is methane. On earth Methane is produced by a variety of processes,
including human activity, volcanic eruptions and biological processes.
These trace gasses break down over fairly short time scales.
I should note that this is “fairly short” as far as geologists are concerned.
Methane is expected to have a life time of a few hundred years in the martian
atmosphere, making its formation very recent in geological terms. This means
that these gases were likely produced in the present era, rather than being a
relic of a time when there were dramatically different environmental conditions
on Mars.
Methane has been observed by the Mars Express orbiter, and
by telescopic observations from Earth. It was also detected by NASA’s Mars
Science Laboratory Curiosity Rover in Gale Crater, which estimated the local methane
concentration to be around 0.7 ppb. Observations of Methane have been
contentious, because it is very hard to make reliable measurements of such
small concentrations. The TGO satellite will produce far more reliable data. It
will confirm the observations of Methane, and will be able to map their source
regions, and study their variations over time.
Since microorganisms produce most of Earth’s methane its
presence on Mars could indicate life. However an abiotic source of methane,
that is one which is not related to biology, could be just as exciting, for us
geologists at least. The hydrogeochemical processes that produce methane at
deep sea vents on Earth could well be responsible for producing it on Mars as
well. This explanation wouldn’t make as many headlines, but would tell us a lot
about subsurface aquifers on Mars, and the chemical processes which are going
on in them.
The TGO can tell us where the methane is coming from, but it
can’t delve into the ground to work out whether it’s being produced by
microorganisms or not. For that we need landers which can conduct experiments
on the surface. These sorts of measurements are called “in situ” data, and can
be used to confirm the observations of remote instruments such as those on TGO.
Getting this in situ data is the goal of the 2020 Lander, which will have a
rover and an extensive scientific payload.
However there is always going to be a limit to what can be
done on Mars. We are getting very good at miniaturising scientific instruments
and shipping them to other planets, but for best results we need to bring
martian material back to earth to examine it here. Such a “sample return” mission
is still a long way from being feasible, but the other main goal of ExoMars is
to demonstrate the technology which will one day allow us to do it.
The 2016 The Schiaparelli lander is an “Entry, descent and landing Demonstrator Module” (EDM), and
it is all about testing the landing technology. Landing on Mars is hard,
and many missions have failed to reach the surface. If we want to land
expensive scientific payloads on Mars, or collect samples for analysis on Earth
then we need a reliable means of landing spacecraft. If this week’s landing
goes without a hitch then that will be great. The stationary lander will be
able to make some useful observations of the martian surface. However its
battery will only last a few days. Its main function is to allow us to fine
tune the landing systems which will take future spacecraft to the surface. To this
end its scientific payload is mainly made up of instruments to study the descent.
Over the coming years the data from the TGO will be used to
inform the aims of the 2020 mission, and the information collected by Schiaparelli
will allow the ExoMars engineers to improve on their landing technology and increase
the likelihood of success.
I wish the ExoMars team the best of luck over the coming
hours. A great many people will be waiting with baited breath to see how this
mission progresses.
Live coverage of the landing from ESA will be taking place over the 19th and 20th of October. See this website for more details.
Live coverage of the landing from ESA will be taking place over the 19th and 20th of October. See this website for more details.
Further Reading:
Information about the ExoMars
Mission at the ESA Website
More information about the
detection of methane on Mars:
Image Credit: Schiaparelli separating from the Trace Gas Orbiter, ESA/ATG medialab
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