After
decades of studying the climate conditions of Mars, scientists have recently
made a breakthrough observation. At the last conference of the American
Geophysical Union (AGU) in San Francisco, Dr. Adrian Brown reported on the
latest results of the instrument that led his team to find water on Mars.
Brown, a research scientist at the SETI Institute who studies climate
similarities between Mars and Earth, says that finding water on Mars makes the
potential for past or even future life on Mars much better.
Brown's
team found a substantial amount of ephemeral (short lived) water ice in the
polar regions of Mars. Early models of the s easonal caps of Mars suggested the
polar caps would be pure carbon dioxide (CO2), and indeed, we now
know that Mars' seasonal polar caps are 99% CO2 ice. Later thinking
on the subject predicted that enough water existed in the Martian atmosphere to
form a band, or "annulus," of water ice around the polar caps as they
receded during springtime. This was subsequently confirmed in the northern
hemisphere, but water ice in the southern hemisphere remained elusive and
difficult to find until now.
The Compact Reconnaissance Imaging Spectrometer
for Mars, or CRISM, is the instrument that made possible the recent
discovery of Brown's team. Johns Hopkins University in Maryland operates CRISM,
which is carried onboard NASA's Mars Reconnaissance Orbiter. CRISM has twenty
times the resolution of past Mars mineral mappers, allowing an unprecedented
analysis of surface content, as well as the first compositional mineral maps of
Mars. It collects a digital image made up of pixels; each pixel spans 15 to 20
meters on the surface of Mars. These pictures are then compiled or examined
individually as surface footprints. "CRISM could take a picture of two
Martian houses, just to give you an idea of how detailed these images
are," Brown explained.
The results
of the CRISM observations identify some striking similarities between the Earth
and Mars. The recent
study of the first CRISM data — reveals frozen H20, which
appears in small patches within and on the edge of Mars' southern polar cap as
it recedes in springtime. In addition to seeking this form of ice, Brown also
studies ice composed of CO2, with his search focused on the south
polar region of Mars. The polar regions of both Earth and Mars have dynamic
effects on the rest of the planet. The Sun's radiation on Earth and Mars has
comparable effects, and mapping of the polar regions has lead some researchers
to suggest the controversial idea that Mars is showing signs of global warming,
much like on Earth.
A close examination
of data from CRISM shows an image timeline of the seasonal south polar ice cap,
as CO2 ice makes the transition directly from a solid to a gaseous
form in a process called sublimation. The sequence of images in this movie
shows the strength of the 1.4 micron absorption band of CO2 in the
seasonal cap of the south pole of Mars. Red colors show deeper absorptions,
typically due to larger grains or greater abundance of CO2 ice. Blue
shows little or no CO2 ice, and green and yellow are in between.
This allows scientists to track the receding edge of the CO2 ice cap
through the spring. Each frame of the movie is a combination of images acquired
by CRISM over a 14-Earth-day period.
The south
polar cap of Mars grows and retracts seasonally, similar to the polar caps on
Earth. As Brown said, "Understanding that whole system as a function of
time is really important and what CRISM
allows us the opportunity to do. And that is the work that we were reporting on
at the recent AGU conference, looking at the spring recession of CO2
ice. We found some pretty interesting, unexpected effects that we haven't been
able to find before with this CO2 ice and water ice
interaction."
Brown and
the CRISM team intend to examine the so-called spring recession data more
closely to determine whether the water ice is present in the form of clouds, or
whether it is part of a surface deposit. The ephemeral nature of these deposits
and their small extent have meant they have been overlooked in the past, but as
CRISM and Mars Reconnaissance Orbiter carry out their continuing mission, the
Mars community is gaining a greater understanding of what is happening in the
most dynamic parts of the red planet.
For more information about Adrian Brown's research on Mars, visit: http://abrown.seti.org
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