2020 will be a banner year
for the exploration of Mars.
In addition to the launch of
NASA's Mars 2020 rover, the
European Space Agency and
Roscosmos are sending the
ExoMars rover to the red planet.
As it descends from its landing
platform, ExoMars will embark on
an enterprising mission: to
uncover buried signs of past or
present life.
The Martian surface is a harsh
environment, bombarded with
cosmic radiation, but the
subsurface
could offer better protection.
For this reason, ExoMars is
equipped with an extending drill
that can retrieve samples
from up to two meters
below the surface.
Studying these samples will be
the job of the Analytical Lab, a
trio of instruments designed
to search for the molecular
fingerprints of life.
The Mars Organic Molecule
Analyzer, or MOMA, is the
largest and most complex
instrument on the rover.
Its mass spectrometer subsystem
and its main electronics were
built and tested at NASA's
Goddard Space Flight Center,
which also contributed
mass spectrometers to NASA's
Curiosity rover
and MAVEN orbiter.
MOMA is designed with a mix of
proven hardware and innovative
new technologies.
Here's how it works: in gas
chromatograph mode, crushed
Martian rock is put into an
oven and heated to 900 degrees
Celsius in just two
minutes, vaporizing the sample.
Molecules of hot gas rise up,
and flow into a narrow, twenty
meter-long tube.
Special coatings inside the tube
cause molecules with certain
chemistries to slow down more
than others, separating the
mixture of molecules over time.
Next, a beam of electrons
ionizes the molecules, giving
them a positive electric charge
and deflecting them towards the
linear ion trap.
The ions are caught by a
fluctuating electric field, and
sent to a detector to
determine their chemical makeup.
While gas chromatography has
been used to study Mars since
the Viking program, MOMA has
a second method for preparing
samples that has never
been used on another planet.
In laser desorption mode, a
sample is placed beneath a
powerful ultraviolet laser.
A beam of energetic light builds
within the laser and fires in a
billionth of a second,
concentrating its energy onto a
spot smaller than
a grain of sand.
This rapidly vaporizes a portion
of the sample, releasing large
organic molecules that could
be broken down by oven heating.
The laser shot also ionizes some
of the molecules, allowing the
vapor to head directly
to the linear ion trap.
Neutral molecules are ejected
by a vacuum, while the remaining
ions are sent to the detector to
determine their chemical makeup.
Laser desorption will enable
MOMA to detect long molecules
like lipids, the building
blocks of cell membranes, a leap
forward in the
search for life on Mars.
MOMA's linear ion trap is
another first
for the red  planet.
It will scan for the
fingerprints of life using
techniques normally confined
to laboratories on Earth.
One technique, called SWIFT,
repeatedly ejects unwanted
molecules from the trap.
Over time this builds up
molecules of interest,
improving detection.
Another technique is tandem mass
spectrometry, or MS/MS, which
identifies large molecules
by breaking them apart and
analyzing their fragments.
By combining SWIFT and MS/MS,
MOMA can determine an individual
molecule's formula and its
structure, both important
criteria in the search for life.
The question of life on Mars
is among the most important in
planetary science, and the
evidence may be buried just
below the surface.
With the help of MOMA, ExoMars
will take us one step closer to
uncovering the answer.
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