High Resolution Images Show Big Differences Between Mars Polar Caps

Donald Savage ,
Headquarters, Washington, DC

(Phone: 202/358-1727)

Mary Hardin

Jet Propulsion Laboratory, Pasadena, CA

(Phone: 818/354-0344)

David Brand

Cornell University, Ithaca, NY

(Phone: 607/255-3651)

Robert Tindol

California Institute of Technology, Pasadena, CA

(Phone: 626/395-3631)

RELEASE: 00-35

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, troughs and flat mesas that give it a holey Swiss-cheese
appearance.

“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
terrain.

“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 seasons.”

“These landforms may be telling us what the South polar cap
is made of,” says Dr. Andrew Ingersoll of the California Institute
of Technology, Pasadena, CA 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
frozen carbon dioxide, otherwise known as 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. These images may help us decide.”

The North polar cap is covered mainly by pits, cracks, small
bumps and knobs that give it a 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.

“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 (JPL), Pasadena, CA, for NASA’s Office of Space
Science, Washington, DC. JPL’s industrial partner is Lockheed
Martin Astronautics, Denver, CO, which developed and operates the
spacecraft. JPL is a division of the California Institute of
Technology.