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Want to Colonize Mars? Aerogel Could Help Raising crops on Mars is far easier in science fiction
than it will be in real life: The Red Planet is an inhospitable world. Among
other challenges, subzero temperatures mean water can persist on the surface only
as ice, and the planet's atmosphere offers little protection to plants (or
people) from the Sun's radiation.
Of course, NASA has plans to eventually put humans on
Mars, using lessons it will learn from its Artemis lunar explorations.
And those humans will need to eat. Being able to produce food on Mars would
help reduce the quantity of supplies consuming valuable space and fuel on
crewed missions to the Red Planet. But figuring out how - and where - to
produce that food, while also being exceedingly careful not to contaminate Mars
with Earth-borne bacteria, are some of the challenges scientists and engineers
face.
In a new paper in Nature Astronomy, researchers propose
that a material called aerogel might help humans one day build greenhouses and
other habitats at Mars' mid-latitudes, where
near-surface water ice has been identified. The study was funded by Harvard
University's Faculty of Arts and Sciences.
Aerogel is a Styrofoam-like solid that is 99% air, making
it extremely light. It's adept at preventing the transfer of heat as well,
making it an excellent insulator; in fact, it's been used for that purpose on
all of NASA's Mars rovers. Moreover, aerogel is translucent, allowing visible
light to pass through while blocking ultraviolet light's harmful radiation. Most
aerogel is made from silica, the same material found in glass.
In an experiment conducted by lead author Robin Wordsworth
of Harvard, 2-3 centimeters of silica aerogel allowed light from a lamp tuned
to simulate Martian sunlight to heat the surface beneath it by up to 150
degrees Fahrenheit (65 degrees Celsius) - enough to raise
temperatures on the Martian surface and melt water ice.
"The study was meant as an
initial test of aerogel's potential as a Martian building material," said
second author Laura Kerber, a geologist at NASA's Jet Propulsion Laboratory in
Pasadena, California.
Kerber participated in a 2015
NASA workshop to identify the best places on Mars to send astronauts. "The
ideal place for a Martian outpost would have plentiful water and moderate
temperatures," she said. "Mars is warmer around the equator, but most
of the water ice is located at higher latitudes. Building with silica aerogel
would allow us to artificially create warm environments where there is already
water ice available."
Broadening the regions on Mars
where humans could grow things also opens up new areas where they could conduct
valuable scientific research, Kerber added.
'Dark Spots' on Mars
The aerogel experiment was inspired
by the heating process that creates so-called dark spots that dot Mars' carbon
dioxide ice caps during the spring. This kind of ice is better known on Earth
as dry ice. Like aerogel, carbon dioxide ice is translucent, allowing sunlight to
heat the surface below. As the soil warms, carbon dioxide gas accumulates
between the ice and the warm surface, eventually causing the ice to rupture.
That, in turn, creates a puff of gas that tosses soil beneath the ice onto its
surface.
The experiment explored a
similar process with aerogel. The paper details how both a solid piece of
aerogel as well as chunks of crushed aerogel can be used to heat the surface
below. The researchers used varying levels of illumination produced by Martian
seasons. The results suggest aerogel could even provide a heating effect
in the bitter Martian winter. In the mid-latitudes, winter nighttime
temperatures can be as cold as minus 130 degrees Fahrenheit (minus 90 degrees
Celsius).
The next step, Wordsworth said,
is taking the experiment out of the lab and into Martian analogues like Chile's
Atacama Desert or Antarctica's McMurdo Dry Valleys. Like Mars, these
environments reach subzero temperatures and are exceptionally dry.
"Our prediction is
that aerogel shielding should provide more efficient heating as it scales in
size," Wordsworth said. "That would be important to see under field
conditions."
Challenges to Be Overcome
While the experiment was an
encouraging proof of concept, Wordsworth acknowledged there are still
significant engineering challenges to overcome. Based on a climate model
produced along with the experiment, it would take lots of aerogel and at least two
Mars years (or four Earth years) of warming to produce a permanent region of
liquid water underneath. Although aerogel is several times lighter than air,
building structures with roofs made out of the
material would require shipping large quantities of it to Mars or somehow
manufacturing it there.
Silica aerogel is very fragile
and porous; layering it within another translucent material, or combining it
with flexible materials, could prevent fracturing. Doing so could increase air
pressure under a structure made with an aerogel roof or shield as well,
allowing liquid water to pool more easily on
the surface instead of vaporizing in the thin Martian atmosphere.
But the study's authors noted
that developing small habitability zones on Mars is more plausible than
attempting to "terraform" the planet, as science-fiction writers have
proposed doing in the past. A NASA
study last year dashed the hopes of thickening
the Martian atmosphere enough to create an Earth-like greenhouse effect.
"Anything that would help make long-term habitability
possible is exciting to consider," Wordsworth said.
More information
about NASA's Mars program is at:
https://www.nasa.gov/mars
https://mars.nasa.gov/
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