New View Of Mars' North Pole Reported In Science

December 06, 1998

Washington DC - Thanks to a new set of topographical measurements from the Mars Global Surveyor spacecraft, the surface features at Mars' north pole are now better known, on average, than some parts of Greenland and Antarctica. The data provide a different and far more detailed picture of the martian north pole than ever seen before and imply that the ice cap not only is smaller than previously thought, but also sits within a depression on the planet. Any water in the region should therefore flow towards the pole rather than the equator, a finding which seemingly runs counter to the prevailing view of polar water flow on Mars--and should thus prompt a rethinking of the planet's global hydrological cycle. These results and others, which have implications for understanding seasonal and long-term climate change on Mars, are reported in the 11 December issue of Science and will be announced at a news conference at the annual meeting of the American Geophysical Union on Sunday, 6 November.

Although Mars' icy temperatures and its dry, apparently lifeless surfaces are very different from conditions on Earth, Mars' climate is more closely related to Earth's than any other planet in the solar system. The fate of water on Mars is key to understanding the planet's evolution and how the differences between the two planets have come about. The north polar ice cap is one of Mars' largest present-day reservoirs of water and other "volatile" substances (which evaporate easily).

Maria Zuber of the Massachusetts Institute of Technology and her colleagues used elevation measurements taken by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor to construct a precise topographic map of the martian north polar region. The results are hundreds of times more accurate than earlier measurements.

Like an ice cube at the bottom of a bowl, the north polar ice cap appears to be nestled within a depression in Mars' surface that is much wider than previously thought. Therefore any liquid water that might exist in an aquifer just below the surface should flow towards the pole rather than the equator, as was previously assumed. Until now, researchers have proposed that ice cap meltwater flowing below ground towards lower latitudes could play a significant role in the planet's global hydrological cycle, but according to the MOLA data this does not seem to be the case. The ice cap also appears to be smaller than earlier measurements had indicated.

Other observations from the MOLA data also shed light on the global water, or hydrological, cycle and climate change on Mars. The ice cap appears to be smaller now than it was in previous, and probably colder, times. The authors found a series of alternating bright and dark bands at the edges of the cap, a record of ice and dust deposits that should reflect changes in the seasons and longer-term climate patterns. The ice cap is also cut by deep canyons and spiral troughs. These features are unlike any found on Earth's ice sheets, but are probably formed by wind-related processes. MOLA also detected the presence of carbon dioxide clouds, which probably condense out of the martian atmosphere in cold winter temperatures.

Identifying the ice cap's volume is an important step in figuring out the total abundance of water presently on Mars. Based on their data, the authors estimate that the ice cap's volume is less than half of the ice volume on Greenland.

A news conference will take place at 12:15 p.m., Sunday, 6 December, at the annual meeting of the American Geophysical Union at the Moscone Convention Center, Room 112, 747 Howard Street, San Francisco, CA. Copies of the paper and related visuals will be available at the news conference and in the Press Room, Room 111. Dr. Zuber will be presenting the paper at 9:30 a.m. Sunday, 6 December.
ORDER ARTICLE #14: "Observations of the North Polar Region of Mars from the Mars Orbiter Laser Altimeter," by M.T. Zuber, O. Aharonson, G.A. Neumann, G.H. Pettengill, P.G. Ford, at Massachusetts Institute of Technology in Cambridge, MA; D.E. Smith, J.B. Abshire, R.S. Afzal, J.B. Garvin, H.V. Frey, X. Sun, and H.J. Zwalley at NASA/Goddard Space Flight Center in Greenbelt, MD; K. Fishbaugh, J.W. Head at Brown University in Providence, RI; A.B. Ivanov, D.O. Muhleman at California Institute of Technology in Pasadena, CA; R.J. Philips, and Washington University in St. Louis, MO; C.L. Johnson and S.C. Solomon at Carnegie Institute of Washington, in Washington D.C.; W.B. Banerdt, T.C. Duxbury at Jet Propulsion Laboratory in Pasadena, CA. M.T. Zuber and G.A. Neumann are also at NASA/Goddard Space Flight Center, in Greenbelt, MD. CONTACT: Maria T. Zuber at 617-253-6397 (phone) or (email). Dr. Zuber will be checking her email while travelling.

If you will not be attending the news conference, for copies of this article please email, call 202-326-6440, or fax the form below to 202-789-0455. For related visuals please contact Heather Singmaster at 202-326-6414 or


American Association for the Advancement of Science

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