May 27, 1998
Profiles of topography collected during April 1998 contain unprecedented new information about the relief of the north polar cap of Mars, as well as its surrounding features, including the expansive north polar sand seas. In addition, the instrument obtained the first direct measurements of cloud heights on Mars, with clustered cloud features appearing most prominently near the edge of the north polar cap.
During April of 1998 the MOLA instrument acquired 59 passes of data which span a region on Mars that extends from approximately 60 degrees north latitude, over the polar cap, and down to around 15 degrees north latitude. These profiles include over 50,000 measurements of north polar cap elevations. The spatial resolution of the MOLA profile measurements is approximately 1,000 feet (330 meters) and the vertical resolution is approximately one foot (30 centimeters).
The MOLA profiles of the northern polar cap show the height of the Martian surface to increase sharply by about 0.5 miles (one kilometer) above the surrounding terrain at the cap edge at a latitude of about 80 degrees north. The elevation of the cap increases toward the pole and achieves heights above the surroundings of 1.25-1.5 miles (2-2.5 kilometers) at the highest latitude sampled, 86.3 degrees.
The topographic profiles reveal striking surface topology of canyons and spiral troughs, which cut through the upper portions of the northern polar cap to depths as great as 3,600 feet below the ice surface. Many of the larger and deeper troughs display a staircase structure, which may ultimately correlate with evidence of seasonal layering of ice and dust observed in Viking images of the cap obtained in the late 1970's.
The MOLA data also have revealed that large areas of the ice cap are extremely smooth, with elevations that vary by only a few feet over many miles. The profiles across the ice cap will be used to understand the processes that shaped the cap, including the deposition of water and carbon dioxide, and the modification by ice flow, solar radiation, wind and mixing with dust. These observations will ultimately be used to help unravel the history of climatic variations on Mars.
MOLA also profiled vast dune fields that surround the polar cap. The dunes are typically 50 to 150 feet (approximately 15-50 meters) tall with crest-to-crest spacings of less than a mile (approximately 1 kilometer) in most cases. Such properties are similar to some forms of terrestrial sand dunes, especially those that form sand seas or ergs in North Africa deserts.
Over half of the MOLA profiles revealed the presence of clouds. Reflections from the atmosphere were obtained at altitudes from just above the surface to over nine miles (less than 1 to 15 kilometers). Most cloud detections were made at high latitudes, at the boundary of the ice cap and surrounding terrain. These observations represent the first direct measurement of the heights of clouds in the Martian atmosphere, making MOLA the first planetary atmospheric lidar. The measurements of the thickness and distribution of atmospheric reflections over the course of the Mars Global Surveyor mission will be used to better understand Martian weather patterns, including the transport of dust and water in the atmosphere.
MOLA observations of the Red Planet will continue as the second part of the Science Phasing Orbit operational phase of the Mars Global Surveyor mission begins in late May, and will continue until September when aerobraking will resume to place the spacecraft in its intended orbital vantage point around Mars.
The principal investigator of the MOLA investigation is Dr. David E. Smith of the NASA's Goddard Space Flight Center in Greenbelt, Md. The MOLA instrument was designed and built by the Laser Remote Sensing Branch of Laboratory for Terrestrial Physics at Goddard. The Mars Global Surveyor mission is operated by the Jet Propulsion Laboratory in Pasadena, Calif..
More details about the MOLA instrument and science investigation can be
found at:
http://ltpwww.gsfc.nasa.gov/tharsis/mola.html.
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