Sky and Telescope - October 2016 - 24

Mars Exploration
Mars. As TGO loops around the planet, the spacecraft
will study sunlight as it reﬂects oﬀ the surface, scatters
in the air above the horizon, and passes through the
atmosphere to the craft when it's ﬂying through Mars's
shadow. TGO will circle Mars every 2 hours, so it will be
eclipsed by the planet 12 times a day (with a few exceptions due to the spacecraft's migrating orbit). During
these frequent occultations, the spacecraft will depend
on two lithium-ion batteries instead of its solar panels,
which wingtip-to-wingtip span 17.5 meters (57.4 feet), or
nearly the length of a bowling lane.
The fourth instrument, the neutron detector, will
determine how much water ice exists within the top
meter of the planet's surface. This detection will be an
indirect one. When cosmic rays slam into the surface,
they free neutrons from the atoms there. These neutrons
scatter every which way, like the splat of a paint-gun
pellet. Some of them even make it all the way to space,
where TGO will catch them. The distribution of their
velocities reveals how much hydrogen comprises the
material they passed through. Since most hydrogen will
be in water molecules, scientists (fairly safely) assume
that any hydrogen they detect is a proxy for water.
Water ice is a big deal for long-term Mars exploration.
Its abundance will inﬂuence future landing-site selections, both robotic and crewed. For instance, those working on NASA's Journey to Mars initiative - which aims to
launch the ﬁrst crewed mission to the Red Planet in 2035
- are currently exploring strategies for extracting water
ice and other resources from the rust-stained Martian soil.

ExoMars Schiaparelli: Fast Facts
Diameter

1.65 m (without heat shield)

Height

1.8 m

Mass

600 kg

Power

battery

Communication

UHF link (2 antennas) with TGO

Science instruments
* science payload: Dust Characterisation, Risk Assessment, and
Environment Analyser on the Martian Surface (DREAMS)
* entry/descent tests: Atmospheric Mars Entry and Landing Investigation and Analysis (AMELIA); Combined Aerothermal and
Radiometer Sensors Instrument Package (COMARS+); Descent
Camera on Schiaparelli (DECA)
* Instrument for Landing - Roving Laser Retroreﬂector Investigations (INRRI)

WHY " S C HIAPARE LLI"?
The lander's name honors the Italian astronomer
Giovanni Schiaparelli (1835-1910), who mapped the Red
Planet's surface and drew the famous canali - dark
lines that started a debate about Martians' existence.

October 2016 sky & telescope

Touchdown
The second part of ExoMars 2016 is Schiaparelli. It's a
lander, not a rover - it's just going to sit there. But it is a
technology testbed for the upcoming rover.
Schiaparelli will separate from TGO on October 16th.
Three days later, it will enter the upper atmosphere in a
daredevil dive of nearly 21,000 km/h (13,000 mph). As it
plummets, the ﬂying-saucer-like lander will measure the
atmosphere's density, pressure, and temperature. Engineers will also use the dive to test the heat-shield design.
In less than 6 minutes, Schiaparelli will fall about
120 km and, thanks to aerobraking, a 12-meter-wide
parachute, and three clusters of hydrazine thrusters, will
slow to a standstill hover 2 meters above the surface (see
illustration, page 23). Then the thrusters will cut and
drop it to the ground. A crushable bottom, similar to a
car's crumple zone, will absorb the thud.
Once on the surface, Schiaparelli will operate on
battery power for 2 to 8 Martian days, or sols, which are
24.7 hours long. It will monitor local weather conditions, including humidity, dust, and wind speed, as well
as electric ﬁelds near the surface, which might help
maintain or even increase the atmosphere's dust levels
(scientists don't yet know, because they've never measured these surface ﬁelds).
Airborne dust could pose a problem. Due to orbital
mechanics, the lander arrives in the middle of the
planet's storm season. Plus, its landing site in Meridiani
Planum - roughly 50 km from where NASA's Opportunity rover is exploring the crater Endeavour - lies close
to a track frequented by dust-laden winds. But storms
usually occur in two peak periods, and Schiaparelli
should arrive after the ﬁrst peak. Regardless, engineers
have designed it to handle blustery conditions.
All this is merely ExoMars's ﬁrst act; next comes the
rover. Originally scheduled for a 2018 launch, the rover
has been delayed to 2020 (S&T: Sept. 2016, p. 9). When
it does reach the Red Planet, it will drill into the surface
and collect samples, both to conduct exobiological and
geochemical research and as a test for an upcoming
international sample-return mission.
ExoMars won't be the only project heading to the Red
Planet that year. NASA's Mars 2020 rover will also cache
samples and look for hints of past life. In addition, it will
test technology to extract oxygen from the atmosphere's
carbon dioxide, in preparation for human exploration.
And the Mars race extends beyond Europe, Russia,
and the United States. Japan, India, the United Arab
Emirates, China, and even the private company SpaceX
(cooperating with NASA) are all exploring ways to reach
the Red Planet or its moons within the next decade. Our
obsession with Mars continues. ✦
Science Editor Camille M. Carlisle would never, ever, ever go
to Mars.

Sky and Telescope - October 2016

Table of Contents for the Digital Edition of Sky and Telescope - October 2016