Contact: Mary Hardin

New high-resolution images from NASA’s Mars Global Surveyor
spacecraft comparing the ice caps at the North and South poles
show the difference between the two regions is in the ‘cheese’.
The North polar cap has a relatively flat, pitted surface that
resembles cottage cheese, while the South polar cap has larger
pits, trough and flat mesas that give it a holey, Swiss cheese

“Looking like pieces of sliced and broken Swiss cheese, the
upper layer of the Martian South polar residual cap has been
eroded, leaving flat-topped mesas into which are set circular
depressions,” said Dr. Peter Thomas of Cornell University,
Ithaca, NY and lead author of the paper. “Nothing like this has
ever been seen anywhere on Mars except within the South polar
cap, leading to some speculation that these landforms may have
something to do with the carbon dioxide thought to be frozen in
the South polar region.”

In a paper to be published March 9, 2000, in the journal
Nature, members of the Mars Global Surveyor imaging team have
described some of the newly discovered differences in polar

“The unusual shapes of the landforms on the North and South
polar caps suggest that these regions have had different climates
and histories for thousands or perhaps even millions of years,”
said Thomas. “We are discovering them for the first time because
Mars Global Surveyor is working to provide high-resolution views
of the tremendously diverse terrain on Mars over all Martian

“These landforms may be telling us what the South polar
cap is made of,” said Dr. Andrew Ingersoll of the California
Institute of Technology in Pasadena and one of the authors of the
paper. “The North residual cap — the part that survives the
summer — is made of water ice. The South residual cap seems to
be made of carbon dioxide or dry ice, but we don’t know if this
is a veneer a few meters thick or a solid block that extends down
2 or 3 kilometers (1.24 or 1.86 miles). These images may help us

The North polar cap is covered mainly by pits, cracks, small
bumps and knobs that give it the cottage cheese look. The pits
that have developed on the surface are spaced close together
relative to the very different depressions in the South polar
cap. These pits probably developed slowly over successive spring
and summer seasons.

“The polar images demonstrate again that understanding Mars’
complicated history requires studying many areas in detail, just
as understanding the Earth does,” Thomas said.

The new images can be seen at and

“If we discovered that both polar caps are mostly water, it
would leave a mystery about why there is so little carbon dioxide
on Mars. Earth has a lot of carbon dioxide, but creatures living
in the ocean have turned it into limestone rocks. Without oceans
or life, Mars should have a lot more carbon dioxide on its
surface than we seem to be finding,” explained Ingersoll.

Mars Global Surveyor is managed by the Jet Propulsion
Laboratory for NASA’s Office of Space Science, Washington, DC.
JPL’s industrial partner is Lockheed Martin Astronautics, Denver,
which developed and operates the spacecraft. JPL is a division of
the California Institute of Technology.


#2000-020 mah