NASA reveals site for next Mars touchdown
August 25, 1999
By Robin Lloyd
Web posted at: 1:07 p.m. EDT (1707 GMT)
CNN Interactive Senior Writer
(CNN) -- Three months from now, NASA's three-legged Mars Polar Lander should touch down 1,200 kilometers from the planet's retreating south polar ice cap for a study of an area of the red planet unlike any previously visited.
The selected landing site, announced at a news conference Tuesday, is on a relatively flat plateau of banded soil that intrigues scientists.
"These are some of the highest regions of the planet because they sit on top of southern hemisphere terrain, which is higher than corresponding terrain in the north," said Richard Zurek, project scientist for the Polar Lander mission.
The layered soil there is evidence of frequent climate changes, like ice ages on Earth. Yet scientists have no idea how old the layers are, whether they are accumulating or being eroded or exactly how the dust, ice and sand built up over time.
The mission managers said the target is devoid of large craters and hills, unlike the surface where NASA's Pathfinder landed in 1997. Pathfinder, cradled in airbags, bounced to a stop in a rocky desert near the martian equator.
The terrain will be safer than the Pathfinder landing site, in part because layers of dust have buried any ancient rocks and craters that exist there.
The Mars Pathfinder landing site (left) compared to landing site for the Mars Polar Lander
The summertime sun never sets at the Mars' south pole during the season that Polar Lander will touch down. The sun will rise to only 30 degrees in the midday sky, bringing temperatures up from minus 100 degrees Fahrenheit below zero to minus 10 degrees and providing enough rays to power the Lander during the daytime.
On December 3, the Polar Lander will begin its Mars atmospheric entry at speeds of 1,000 mph. It will slow its descent with a parachute and retrorockets in preparation for a 5 mph touchdown. During its 90-day study of ice beneath the martian surface, the probe will also look for evidence of seasonal water and study carbon dioxide and dust cycles on Mars.
Polar Lander is one of a pair of solar-powered spacecraft designed to examine the martian climate. Its partner, the Mars Climate Orbiter, was launched in December 1998 and will orbit the planet while the lander gathers data.
The Climate Orbiter is set to arrive at Mars on September 23, after completing 200 trips around the planet, dipping into the martian atmosphere to slow down and circularize its orbit. The orbiter will do some mapping and transmit signals from the lander to Earth during the mission.
Several days after touchdown, a robotic arm on the lander will begin to scoop up samples of the martian soil and "cook" it in search of minerals that include water and carbon molecules.
"If we find evidence that (those) minerals are there, there must have been a time in Mars' early history when there was standing water on Mars' surface," Zurek said.
Ever since data was returned from the first Viking landings on Mars more than 20 years ago, scientists have believed that Mars was flooded by water billions of years ago. But it is the possible presence of standing water -- a requirement for life -- that is most tantalizing to scientists.
The landing site features very low ridges and grooves that suggest the surface has been eroded over time by growing and retreating ice slabs.
The proposed site also includes two craters, each about the width of a baseball stadium, with the smaller one thought to be 7 meters (23 feet) deep and the larger one estimated at 17 meters (56 feet) deep.
Mounds and valleys within the site range from a few meters to as much as 100 meters (328 feet) across, rising up only a few meters high.
This summer, which marks the end of winter on Mars' south pole, the surface there is mostly covered with carbon dioxide frost, which is vaporized by the morning sun. That frost will have evaporated by the time of the December landing.
The lander also carries three cameras, a microphone for listening to sounds and two twin microprobes that will be released from the mother ship to penetrate the polar cap in search of water ice.
Typical of most missions, Polar Lander engineers wanted a landing site that is relatively flat and smooth, while scientists wanted one that also was close to more complex terrain -- in this case, the layered deposits.
This figure shows the location of the primary (purple) and secondary (white)
landing areas, which were selected on the basis of data from Mars Global Surveyor
The Polar Lander site represents a compromise, with the chosen landing site at 76 degrees south latitude and 195 degrees west longitude, within the area that scientists initially recommended.
During June and August, Global Surveyor scanned strips of the planet's surface in a broad area surrounding that proposed site, some at a sharp resolution of 4 meters (13 feet) per picture unit.
Global Surveyor and the two Polar Lander and Climate Orbiter missions are managed by NASA's Jet Propulsion Laboratory. The latter two missions, along with the microprobes, cost $265 million to develop and build.
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