Scientists have known for years that the polar caps on Mars shrink and grow
between the Martian summer and winter seasons. But they wondered just how
much carbon dioxide 'snow' is deposited each season? Are the frost
deposits more like snow or more like ice? What role do the ice caps play
in seasonal changes on Mars? Now new research from MOLA, the laser
altimeter aboard the Mars Global Surveyor,
may provide answers to these questions.
Elevation measurements taken by MOLA in combination with gravity
determined by tracking the MGS spacecraft have been used to
measure seasonal changes in the thickness of seasonal frost deposits and
to provide the first direct measurement of their density.
These two images use MOLA topography. The image on the
left is colored with a mosaic from the MOC camera. The image on the right
is colored according to the relative height of the surface
Over the course of a Martian year, which consists of 687 Earth days, as
much as a third of Mars' tenuous carbon dioxide (CO2) atmosphere "freezes
out" at the polar caps during the winter in the northern and southern
hemispheres. A team consisting of Dr. David E. Smith of NASA's Goddard
Space Flight Center (Greenbelt, Md.), and Drs. Maria T. Zuber and Gregory
A. Neumann of the Massachusetts Institute of Technology (MIT), used MOLA
data to measure the changes in the height of the polar caps every two
weeks. They showed that small changes in surface height correlate with the
expected times of deposition and evaporation of CO2 from the surface. The
group also measured miniscule changes in the gravity field of Mars due to
the movement of carbon dioxide, which allowed them to make the first
measurement of the density of surface frost deposits.
The MOLA results show that a maximum of 1.5 to 2 meters of frozen material
are deposited during the Martian winter. During the summer, the frozen CO2
evaporates and returns to the atmosphere. These two graphs show the
maximum amount of 'snow' that accumulated over the northern hemisphere
"Snow on Mars is composed of dry ice and last year it reached a maximum
depth of 1.5 to 2 meters near both the north and south poles," explained
Smith, Principal Investigator of the laser altimeter investigation and lead
author of the study published in the December 7 issue of Science.
These two graphs show the maximum amount of 'snow' that accumulated over
the northern hemisphere [left] and southern hemisphere [right]. Click to view animation
"Snow on Mars is denser than it is on Earth, being more ice-like than
powdery," noted Zuber, the Deputy Principal Investigator of the altimeter
investigation. To isolate the signals, the group measured changes of 10
centimeters in the height of the surface of Mars, and changes of a couple
parts per billion in the planet's global mass distribution.
MOLA data was also used to track elusive Martian clouds linked to the
frozen deposits. The thin lines in these images are the tracks of the
laser bouncing off of the clouds. When the tracks are added together, we
can see how the range of the clouds (white overlay) change during the
The images show the clouds
associated with the CO2 precipitation in the northern hemisphere [first
image] and the southern hemisphere [second image].
Click to view animation.
Carbon dioxide is overwhelmingly the most abundant gas in the martian
atmosphere and an important greenhouse gas. The studies of the CO2 clouds
will allow a better understanding of the present atmosphere, which improves
the ability to target future landers, and provides important information
for understanding the evolution of the atmosphere over time.
"Characterizing the present-day behavior of CO2 is a necessary first step
towards understanding the past climate on Mars," noted Neumann.
Links & Resources
For more information, including hi-res images, please see the press
release this article was adapted from.
Seasonal Variations of Snow Depth on Mars, Science, Vol 294, December
For more figures and animations, see: