New Mars Close-Ups Show Diverse Terrain
Mars Close-Ups Show Diverse Terrain
Thousands of newly released portraits of Martian landscapes from NASA’s Mars Global Surveyor spacecraft testify to the diversity of geological processes which have sculpted the surface of our neighboring planet. The Mars Global Surveyor has been orbiting the red planet since Sept. 12, 1997. Its mission has examined the entire Mars surface and provided a wealth of information about the planet’s atmosphere and interior.
|The camera aboard the Mars Global Surveyor spacecraft captured this image of the strange "taffy-pull" terrain of northwestern Hellas Planitia on the surface of Mars. The origin of the pattern is unknown, but may be related to the erosion of different layers of bedrock and mass movement of debris. Credit: NASA/JPL/Malin Space Science Systems,MSSS|
The first image of Earth ever taken from another planet that actually shows our home as a planetary disk was captured by the Mars Orbital Camera on May 8th.
Swirling textures that some scientists call "taffy-pull terrain" fill one new image (right) from the plains of southern Mars, for example. Other images reveal details of features such as wind-whipped polar dunes and steep-sided valleys carved by flowing water or lava.
|Frost in Charitum Montes. 10 June 2003, MOC2-387|
Credit: NASA/ JPL/ MSSS MOC
"Mars just keeps astounding us with its complexity," said Dr. Ken Edgett, staff scientist for Malin Space Science Systems, San Diego, which built and operates the Mars Orbiter Camera.
The new group of images was taken between August 2002 and February 2003, then validated and archived by the camera team. It includes many views of north polar terrain, extremely clear-atmosphere views of a deep southern basin named Hellas Planitia, and a variety of Martian landforms between the north pole and the southern middle latitudes. Hellas Planitia is an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.
The pictures show Martian surface details down to the size of a large sport utility vehicle.
Evaluation of landing sites for NASA’s Spirit and Opportunity, two Mars Exploration Rover spacecraft due to land on Mars in January 2004, relied heavily on mineral mapping, detailed imagery and topographic measurements by Global Surveyor. The landing locations under scrutiny now were chosen because of strong signs that they may have held bodies of water at one time. One site, known as Gusev Crater, looks like a big lake bed with a winding riverbed feeding into it, Murphy said. The other site, Meridiani Planum, has the spectrographic signature of a mineral called gray hematite, which usually forms in the presence of liquid water. The two sites, both slightly south of the equator, are on opposite sides of the planet. By late October, officials at NASA Headquarters will have to commit to the rovers’ landing sites.
The mysteries of tallying a good water balance for Mars has been a focus of searches within the image libraries taken on-orbit. The mission so far has shown layered sedimentary deposits in crater basins. It has also discovered what appear to be seepage gullies caused by recently running water, in regions of Mars believed to be far too cold for liquid water to flow.
|Layered Material in West Arabia Terra Crater. 4 December 2000 — MOC2-261 |
Credit: NASA/ JPL/ MSSS MOC
If Mars was wet once in its geological history, it is likely not wet today–or at least too cold for water to flow. The evidence for this " wet and cold " scenario on Mars derives mainly from lower erosion compared to even the driest places on Earth.
As is often the case, these images have led to new questions. For example, if there are so many places where the martian landscape appears to have been altered by running water, why hasn’t the TES (Thermal Emission Spectrometer) instrument aboard MGS found any evidence of carbonates on Mars? ( Carbonates are typically formed on Earth when water evaporates from ponds or lakes.)
Another vexing question is: Where has all the water gone that many scientists believe once flowed on Mars? Some of it can be seen in the form of ice deposits of the northern polar cap. But the rest of it seems to have vanished. Did it evaporate into space? Did it somehow go underground ? No one knows for certain.
Many thermodynamic considerations may also rule out the existence of liquid water on the surface of Mars. For example, the extremely low pressures typical of Mars may be below that of the water triple point. If low pressures are below that of the solid-water-gas transition, or water triple point (6.1 mbar), then any ice would evaporate or sublime rather than flow as a liquid.
In addition to semi-annual releases of large collections of archived pictures, the Mars Orbiter Camera team posts a new image daily and recently began soliciting public suggestions for camera targets on Mars.
NASA’s current Mars landing mission will be a pair of Mars Exploration Rovers (MERs), similar to the 1997 Pathfinder/Sojourner. Those were launched in June and July 2003 and arrive at Mars as early as January 4, 2004. The MERs will study minerals on the Martian surface up-close, searching in particular for further evidence of water-altered minerals.
|Clouds over the Tharsis Volcanoes. 13 March 1998 — MOC2-39 |
Credit: NASA/ JPL/ MSSS MOC
The European Space Agency also plans a rendezvous mission to Mars in 2003, a combined orbiter and lander. The lander, Beagle 2, will conduct biochemical experiments designed explicitly to detect evidence of past or present life on Mars. These will be the first direct Martian life-detection experiments conducted in nearly 30 years. The only previous biological experiments were performed by instruments aboard the two Viking landers that touched down on Mars in 1975.
Speculation about life on Mars has fascinated people since Percival Lowell, founder of the Lowell Observatory in Arizona near the turn of the 20th century, wrote about a system of canals on Mars and suggested they were a sign of civilization. As astronomers have learned more about the planet, the conventional wisdom has gone through some rather wide swings, New Mexico State University planetary scientist Jim Murphy noted. "When the first spacecraft, Mariner 4, flew by Mars 38 years ago and took 21 pictures, it saw only 1 percent of the surface of the planet," he said. "It was heavily cratered like the moon, suggesting the planet was biologically dead."
But with subsequent missions, "we saw the entire planet, and we saw volcanoes, and we saw the Mariner Valley, and we saw that one hemisphere is heavily cratered but the other is not." Under current conditions, water can exist as a vapor or as ice on the surface of Mars but it is not stable in liquid form because the planet’s atmosphere is too thin. Whether liquid water ever existed on the surface, and whether it might exist now beneath the surface, are still unanswered questions.
"If these rovers can convincingly demonstrate that there was substantial liquid water at some point, that would be an important finding," Murphy said. On the other hand, if the rovers find no evidence of water at these two sites, which were chosen because they seem to be compelling candidates for signs of water, "that would be interesting, too, and other theories will need to be developed," he said.
The Jet Propulsion Laboratory, Pasadena, Calif., manages the Mars Global Surveyor mission for NASA’s Office of Space Science, Washington. JPL is a division of the California Institute of Technology in Pasadena. JPL’s industrial partner is Lockheed Martin Space Systems, Denver, which built and operates the spacecraft.