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December 06, 2001 - (date of web publication)

LASER ALTIMETER PROVIDES FIRST MEASUREMENTS OF SEASONAL SNOW DEPTH ON MARS

A global view of how Mars changes with the seasons has been provided by extremely precise observations from two investigations on NASA's Mars Global Surveyor (MGS) spacecraft.

True color image of Mars' North Pole
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True color image of Mars' South Pole
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False color image of Mars' North Pole
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False color of Mars' South Pole
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Mystery of the Martian Snow
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 a laser onboard the Mars Global Surveyor may provide answers to these questions.

The Poles of Mars: These images of the north and south poles use precise measurements from MOLA to generate a 3-D topography view of Mars. The images on the left are colored by mosaic provided by the MGS Mars Orbiter Camera (MOC). The images on the right are colored according to the relative height of the surface features. Scientists uses a special palette to color MOLA topography. The higher relative elevations are indicated by warm colors and lower elevations are shown by cool colors.
Click here for the color palette.
[Credit: NASA/GSFC/JPL/MOLA Project/Malin Space Science Systems]

Elevation and gravity measurements of Mars from MGS have been used to measure seasonal changes in the thickness of seasonal frost deposits and to provide the first direct measurement of their density. The observations were obtained from the Mars Orbiter Laser Altimeter (MOLA) and the spacecraft's radio tracking system.

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" 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, measured changes in the height of the Martian surface 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.

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Ski Mars -- Martian Snow Depth Revealed

Scientists made precise measurements from the orbiting laser over the course of the Martian year to create a portrait of the changing depth of the frozen carbon dioxide (CO2). 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 [first image and southern hemisphere [second image].
Click here for animation.
[Credit NASA/MOLA Project]

"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.

"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.

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Clues from the Clouds

Scientists were also able 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. Scientists add the tracks together can see how the range of the clouds (white overlay) change during the Martian year. The results will allow a better understanding of the Martian atmosphere, which will improve the ability to target future landers. Characterizing the present-day behavior of CO2 is a necessary first step towards understanding past climates on Mars. The images show the clouds associated with the CO2 precipitation in the northern hemisphere [first image] and the southern hemisphere [second image].
Click here for animation.
[Credit NASA/MOLA Project]

The results will allow a better understanding of the Martian atmosphere, which will improve the ability to target future landers. In addition, carbon dioxide is the most abundant gas in the atmosphere of Mars and it is a greenhouse gas. "Characterizing the present-day behavior of CO2 is a necessary first step towards understanding past climates on Mars," noted Neumann.

Mars Global Surveyor is currently in its extended mapping mission, which runs until April 2002. The MOLA instrument was designed and built by the Laser Remote Sensing Branch of the Laboratory for Terrestrial Physics at Goddard. The MGS Radio Science experiment is implemented from the Center for Radio Astronomy of Stanford University, Palo Alto, Calif. The Mars Global Surveyor mission is managed for NASA's Office of Space Science, Washington, D.C., by the Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology.

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High resolution images:
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