Patina on Mars
The dustiest place in the solar system may be getting a new global dusting. According to the the Associated Press, a University of Colorado geologist and other Mars researchers are watching a dust storm that has started churning on that planet, and if it grows it could complicate the landing of a NASA rover in less than three weeks. Global dust storms on Mars –usually beginning in the southern hemisphere–can obscure many surface features.
|Viking Lander-1 (1976) showed dramatic changes during dust storm activity. The appearance of the sky changes with the atmospheric dust content. Although the colors shown here are processed, not real, they do show relative changes. There was a dust storm covering the VL-1 site on Martian day (1742) or sol 1742 (1 Martian year=669 Earth days). High winds on Mars create more dust than any hazard one might expect from a Kansas-like tornado–the air pressure is small and atmosphere so thin (<1% or 1/150th of Earth’s) that more likely difficulties are the mess a dust storm creates than the net force other than upon descent. Even a 100-mile per hour gale on Mars packs the gentle push of a 10 mile per hour breeze on Earth In 1971, Mariner 9 and 2 USSR missions all arrived during a dust storm.At the Viking site, the composition of the atmosphere changed too. At the Chryse site, the amount of carbon dioxide increased by about 5 times, and the amount of oxygen increased by about 200 times in little more than one sol.
This combination of winds, weathering and ‘rusting’ of the soil gives the face of Mars a dynamic weather system. For individual rocks, the effects are similar to what happens to antiquities on Earth: the change in color and chemistry gives the artwork its patina.
|Martian atmosphere and weather awaits the Exploration rovers
Credit: NASA/ JPL/ MSSS MOC
‘Usually [dust storms] appear and die out in a few days to a week, or they expand into global storms. We don’t know what’s going to happen with this one,’ said Bruce Jakosky, the CU geologist who served on the site selection committee for NASA’s $820 million Mars Exploration Rover mission. The dust storm was spotted late last week and now covers a large region of the planet’s northern hemisphere, Jakosky said Sunday during a Mars exploration workshop. He said if dust obscures sunlight, the rover’s solar panels would have less power to use. ‘It’s too early to know if this is something to worry about,’ Jakosky said. ‘But anything like this that happens two to three weeks before a landing is a big deal.’
Potential winds are another concern, because the spacecraft will be landing during a season that is favorable to global dust storms on Mars. When the first spacecraft, Mariner 4, flew by Mars nearly forty years ago and took 21 pictures, it saw only 1 percent of the surface of the planet. It was heavily cratered like the moon, suggesting the planet was biologically dead. When Mariner 9 followed up and more current missions have revealed a more interesting and potentially ‘cold, wet’ picture of what is happening, a number of dust storms have complicated the timing of the observations. Responding to seasonal changes in the heat generated by solar radiation, localized dust storms occur and sometimes grow in strength until they cover the entire planet, a fact with which Mariner and Viking specialists were familiar. Global dust storms appear to be a phenomenon unique to Mars, which lacks large bodies of water that would prevent their buildup.
Atmospheric weathering of the primitive crystalline rocks on Mars has reduced them to fine particles that have oxidized and combined chemically with water to produce the reddish minerals so apparent in color images. Whereas on Earth the dominant weathering process has been from the movement of liquid water, on Mars the primary agent of change has been the wind. It erodes the landscape, transports the dust, and deposits it elsewhere on the planet. Pictures taken by orbital cameras reveal deep layers of wind-borne sediment in the polar regions, while dunefields of Martian dust and sand much larger than those on Earth have been observed near the north pole.
For the forthcoming missions in December and January, "one of the most important jobs for our Pancam camera will be to take pictures of the sun. Part of the reason we’re going to do this is to figure out how dusty the martian atmosphere is: the more dust there is in the sky, the darker the sun will look," wrote the principal investigator for the science package on the Mars Exploration Rovers, Dr. Steven Squyres, of Cornell. "The really important reason, though, is to figure out which way is north. Mars doesn’t have a magnetic field, so we can’t use a compass to figure out directions. Instead, we use Pancam to see where the sun is in the sky, and then use that information to work out which way is which".
Between NASA’s Jet Propulsion Lab and Cornell’s science package, Squyres has had to prepare for a host of dust related issues that may affect the timing of certain instruments on-board the rovers. He wrote in his mission diaries: "Our Microscopic Imager has to have a dust cover. After all, if you’re going to be waving a sensitive scientific camera around on the surface of the dustiest planet in the solar system, it makes sense to have a cover to keep the lens clean. And the cover has to be transparent. We use a motor to open and close it, and the motor is a very reliable one. But even so, if it fails for some reason, we want to be sure we still can take pictures…Lori Shiraishi and a couple of the other mechanical wizards at JPL looked real hard at the thing, and somehow managed to come up with a special tool that let them snake their way in there, get to the cover, and get it off the camera. If they weren’t mechanical engineers, I think they’d be safe crackers".
The color calibration of the Pancam is strongly affected by dust in the atmosphere, just as terrestrial dust scatters light here on Earth and casts a blue sky during the day. On Mars, the sky is pinkish-orange, depending on local conditions. The Pancam has its own color-calibration targets to adjust for changes in local dustiness, but as Bill Nye, project lead for analyzing solar shadows on Mars for his Marsdial project, "If it’s dusty out, we won’t do the sundial observation time-lapse that day. But, the photometric calibration targets are still useful on dusty days. They have color patches and reflective surfaces, and so on. If the shadow is washed out by diffused light, well, the useful effects of pink or orange shadows have to be inferred and approximated without observation. As far as I know, the pan-cams are to be run every day or sol. The useful time for the missions and the cameras is probably going to depend on how much dust settles on the solar panels. It’s an odd or surprising constraint. But that’s it, if nothing else goes wrong. We may be able to fire the space crafts back up during the next Martian summer. We’ll see, perhaps literally."
Three spacecrafts are now hurtling toward the Red Planet to look for evidence that it might once have been wet enough to sustain life.
|Rugged terrain on Mars
Credit: NASA/ JPL/ MSSS MOC
Experiments performed by the MERs will help to determine whether water might have once existed in volume on the red planet. The two Mars Exploration Rovers are targeting what imagery indicates might have been ancient dry lake beds and other geologically interesting sites in early 2004. Matt Golombek, who was the project scientist for the 1997 Pathfinder/Sojourner mission, believes that "the MER is exactly the next step beyond what Pathfinder did." Because it will enable a detailed study of the mineral composition of Martian rocks and soil, it will tell scientists far more than was previously known about the history of water on Mars.
Images released by the orbiting instruments around Mars.
Solar storms, devils, dunes, and gullies (Released 12 December 2003)
|Solar storms, devils, dunes, and gullies (Released 12 December 2003)
Image Credit: NASA/JPL/Arizona State University
Man, there sure is a lot going on here! This image was acquired during the peak of the late October record breaking solar storm outbursts. The white dots in this image were in fact caused when the charged particles from the sun hit our camera. One can also see the enigmatic gullies, dark barchan sand dunes and numerous dust devil tracks. This image is in the Noachis region of the heavily cratered southern hemisphere.
Left: Latitude -42.1 Longitude 328.2E (31.8W) Image Size (km) 62.1×26.2 Mars 2001 Odyssey, Thermal Emission Imaging System (THEMIS), Mars Orbital Laser Altimeter (MOLA) Team
Buried Mid-Latitude Craters
|Buried Mid-Latitude Craters MGS MOC Release No. MOC2-577, 17 December 2003
Image Credit: Mars Global Surveyor, Malin Space Systems
This September 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows six circular features, three of which exhibit concentric, or "bullseye," patterns within them. Each circular feature is the remains of a partly-buried, partly-eroded, and partly-filled meteor impact crater. These occur in northeastern Arabia Terra. Areas such as this, located near the middle latitudes of Mars, commonly have a "scabby" or roughened appearance. The cause of this "terrain roughening" texture is unknown, although some scientists have speculated that it might result from the erosion and removal (by way of sublimation) of ground ice. This idea remains highly speculative. These features are located near 28.4 degrees N, 317.5 degrees W. The image covers an area 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.
About the Orbital Missions
By launching the Mars Global Surveyor (MGS) spacecraft in November 1996, NASA and the Jet Propulsion Laboratory began America’s return to Mars after a 20-year absence. The Surveyor spacecraft is a rectangular-shaped box with wing-like projections extending from opposite sides. When fully loaded with propellant at the time of launch, the spacecraft weighed only 1,060-kilograms (2,342 pounds). The spacecraft travelled nearly 750 million kilometers (466 million miles) over the course of a 300-day cruise to reach Mars on September 11, 1997. During mapping operations, the spacecraft circled Mars once every 118 minutes at an average altitude of 378 kilometers (235 miles). After mapping finishes, the spacecraft will function as a communications satellite to relay data back to Earth from surface landers launched as part of future Mars missions.
2001 Mars Odyssey launched on April 7, 2001, and arrived at Mars on October 24, 2001. The mission is mapping the amount and distribution of chemical elements and minerals that make up the Martian surface. The spacecraft especially looks for hydrogen, most likely in the form of water ice, in the shallow subsurface of Mars. One of its three primary instruments is called THEMIS (Thermal Emission Imaging System), for determining the distribution of minerals, particularly those that can only form in the presence of water. It also provides the communications relay for U.S. and international landers, including missions in NASA’s Mars Program, the Mars Exploration Rovers. The name "2001 Mars Odyssey" was selected as a tribute to the vision and spirit of space exploration as embodied in the works of renowned science fiction author Arthur C. Clarke.