Don Savage
NASA Headquarters
Washington, DC
202/358-1727

Mary Hardin
Jet Propulsion Laboratory
Pasadena, CA
818/354-0344

Cynthia M. O'Carroll
Goddard Space Flight Center
Greenbelt, MD
301/614-5563

NASA'S GLOBAL SURVEYOR SEES POSSIBLE CLIMATE CHANGE ON MARS


The planet Mars we know today is a cold, dry, desert world, but suppose the martian climate is changing even now, year-to-year and decade-to-decade?

New observations made by NASA's Mars Global Surveyor spacecraft are expanding our understanding of the martian climate and may indicate that the climate on Mars is changing significantly even today, suggesting even larger climate changes have occurred during the planet's recent history and may do so again in its future. The observations were made during a full martian year, 687 Earth days.

If this is so, Mars might someday become warmer and wetter as some scientists suggest it was in its early history. Papers detailing these observations are published in the Dec. 7, 2001 issue of Science magazine.

"If the environment of Mars has really changed by as much and over as short a time-scale as our observation implies, there should be attributes of Mars that reflect these changes that may be measurable by landers. If Mars had a higher atmospheric pressure in the not too distant past, it is more likely that water was present as a liquid near the surface," said Dr. Michael Malin, principal investigator for Global Surveyor's camera system at Malin Space Science Systems, San Diego.

Liquid water is required to support known forms of life and the presence of liquid water on Mars would make it more likely life might once have been found there.

Images taken by Global Surveyor's camera system show pits located at the southern polar ice cap of Mars, often referred to as the "Swiss cheese" terrain, have dramatically increased in diameter indicating the material has evaporated rapidly when compared to last year.

"The amount of change is much larger than any previous change we've seen on Mars and it is much larger than can be explained by the evaporation of water ice. We have calculated that the only material that could have changed this much is carbon dioxide ice, what we know as dry ice," said Malin. "This means that the Mars environment we see today may not be what it was a few hundred years ago, and may not be what will exist a few hundred years in the future."

A separate observation is providing more detail about the behavior of carbon dioxide -- a 'greenhouse gas' believed to warm climates when its atmospheric concentration increases -- in the martian climate. The spacecraft's laser altimeter and radio tracking system have made precise measurements of the amount and density of carbon dioxide snow in both polar regions that gives scientists the first global measurement of the seasonal exchange of carbon dioxide between the atmosphere and surface.

Due to the tilt of the planet, Mars has seasons just like Earth. Scientists have known for many years that the most important seasonal change on Mars is the "freezing out" of carbon dioxide from the atmosphere during the autumn and winter in the form of dry ice frost and snow, and then the evaporation of the surface frost in spring and summer as carbon dioxide returns to the atmosphere. Over the course of a martian year, as much as a quarter of the atmosphere freezes out, but until now scientists didn't know precisely where and how much dry ice frost and snow would pile up on the surface.

"We have measured how deep the dry ice snow got on Mars over the course of a year. We have also measured the corresponding tiny change in the gravity field due to carbon dioxide being transported from one pole to the other with the seasons," said Dr. Maria Zuber, deputy principal investigator of the laser altimeter, at the Massachusetts Institute of Technology and Goddard Space Flight Center. "Snow on Mars is denser than snow on Earth and is really more like ice than snow. To better understand weather and climate on Mars we want to characterize the behavior of carbon dioxide on Mars on time scales ranging from hours to billions of years. Understanding the present carbon dioxide cycle is an essential step towards understanding past martian climates."

"We have measured when and where the carbon dioxide is over the entire surface of Mars. These observations will help us develop better models of the Martian weather and climate; there are also major implications for important operational activities in the future such as sending landers to the polar regions where a record of geologically recent climate change may be preserved," Zuber continued.


Pictures and additional information about these observations can be found at:

/snow_paper.html

NASA's Jet Propulsion Laboratory manages the Mars Global Surveyor mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology, Pasadena, Calif.