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Planetary News: Mars (2006)Mars Reconnaissance Orbiter (MRO) Delivers New Martian Clues ... Even Before Science Mission BeginsBy A.J.S. Rayl
The Mars Reconnaissance Orbiter (MRO) sent home a lot more than breathtaking orbital images during the transition week of instrument testing that took place about a couple of weeks ago. As it turns out, the science data has already revealed new clues about both recent and ancient environments on the Red Planet, according to NASA officials -- and the science phase of the mission hasn't even officially begun. Planetary scientists are looking to MRO to answer questions about the history and distribution of Mars' water by combining data from its atmospheric sounder, context camera, ground-penetrating radar, global color camera, high-resolution camera, imaging spectrometer, radio, and accelerometers. During the critical week of testing -- September 29 through October 6 -- MRO's instruments were put through their various configurations and tested, and are "working perfectly," Steve Saunders, MRO program scientist from NASA Headquarters, announced during a briefing in Washington D.C., earlier this week. "The teams are getting amazing science data," he added, and "are ready to fulfill the mission's science objectives and to support other Mars missions." In fact, the instruments returned a whopping 100 gigabits of data, Richard Zurek, MRO project scientist, of the Jet Propulsion Laboratory (JPL), told the planetary community at the American Astronomical Society Division for Planetary Sciences -- aka DPS -- meeting at the Pasadena Convention Center last Friday. [A gigabit is a unit of information in computer storage terminology, often abbreviated Gbit or Gb. 1 gigabit = 109 = 1,000,000,000 bits.] The level of detail coming back, particularly in the High Resolution Imaging Science Experiment or HiRISE camera, is "incredible," he told the assemblage at one of the Mars sessions. That, arguably, is an understatement. The HiRISE camera's image of the rover Opportunity, which was released October 6, put Mars back in the headlines again and was astonishing to view for the first time, by virtually all accounts. The detail is so good that the rover's tracks can be seen meandering all the way back to Purgatory Dune, where the rover became stuck for more than 5 weeks in the spring of 2005. "And you can clearly see the mess we made there," Steve Squyres, principal investigator for the rovers, told The Planetary Society.
MRO's instruments observed and imaged dozens of sites that reflect various different episodes in Mars' history and which together served to provide a well-rounded test for the capabilities of each. In that data, the scientists have found: • Details in the shapes and icy composition of geologically young layering near the Martian north pole; • A mid-latitude valley where upper layers have been eroded away to reveal a clay layer that formed a few billion years ago, when wet conditions produced the clay; and • Fine-scale details of more recent gullies in a southern-hemisphere crater, adding evidence that they were carved by flowing water. And it really was – only a test. In Chasma Boreale, a vast valley that juts into the north polar ice cap, the orbiter's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) -- which takes pictures both in visible-light and infrared wavelengths useful for identifying the composition of a target -- observed layers that vary in soil composition and in how much ice is mixed with the soil. A dark underlying layer contains little ice, but just beneath it lies ice-rich material resembling higher layers. The polar cap has long been recognized to contain layers composed of dust and ice, and hence has been named the polar layered deposit. This sits atop an underlying "basal unit." The upper part of the basal unit is dark at visible wavelengths and steeply sloped, whereas the lower part of the basal unit is brighter, redder, and layered like the polar layered deposits. The chasma floor is cratered, and in the foreground of the image pictured in this article, it is shown to be covered by dunes that are outliers of a north polar sand sea that surrounds the polar cap. The polar layered deposits and the basal unit form a steeply sloping scarp about 1.1 kilometers (0.7 miles) high.
In the new CRISM images, "you see more-ice-rich and less-ice-rich layers, which tells you that conditions changed from the time one layer was deposited to the time another layer was deposited," explained Scott Murchie, of Johns Hopkins University Applied Physics Laboratory (JHUAPL), the principal investigator for the spectrometer, at the press briefing. "These layers are geologically young -- on the order of thousands or millions of years -- and may hold clues about climate cycles." CRISM's mission is to find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. Its image of the Chasma Boreale region shows a number of previously unrecognized characteristics of the polar layered deposits and the basal unit: • First, the ice-rich polar layered deposits exhibit coherent banding both at visible and infrared wavelengths. This banding shows a history of differences in the abundance of dust that accumulated in polar ice, differences in ice grain size, or both; • Second, both parts of the basal unit are depleted in ice, except for triangle-shaped regions on the side of the scarp; • Third, the spectral properties of the brighter, layered lower basal unit resemble those of the polar layered deposits. In contrast, the upper basal unit is distinct from both of them; and • Finally, spectral properties of the foreground dunes closely resemble those of the darkest layers within the upper basal unit, and may be debris from it. CRISM -- which hails from The Johns Hopkins University Applied Physics Laboratory, and includes expertise from universities, government agencies, and small businesses in the United States and abroad -- will also watch the seasonal variations in Martian dust and ice aerosols, and water content in surface materials, which should lead to a better understanding of the climate.
A lower-latitude target for the MRO instruments was Mawrth Vallis. The OMEGA spectrometer on the European Space Agency's Mars Express orbiter previously discovered ancient deposits of phyllosilicate (clay) minerals there, minerals that could form only if water were present for a long time. MRO's CRISM has complemented that finding by resolving smaller-scale compositional features and detecting differing clay mineral content, specifically identifying aluminum-rich and iron-rich clays, each with a unique distribution. On Earth such clays occur in (among other environments) weathered volcanic rocks and hydrothermal systems, where volcanic activity and water interact. On Mars, these clay-rich areas show some of the best evidence for conditions possibly favorable for life on ancient Mars, according to Murchie. Throughout the week of testing, the Mars Color Imager (MARCI), from Malin Space Sciences Systems (MSSS) in San Diego, acquired terminator (transition between nighttime and daytime) to terminator swaths of color images on every dayside orbit, as the spacecraft moved northward in its orbit. The south polar region was deep in winter shadow, but the north polar region was illuminated for the entire Martian day.
During the primary mission, such swaths taken by MARCI will be assembled into global maps that portray the state of the Martian atmosphere -- its weather -- as seen every day and at every place at about 3 p.m. local solar time. Combined with wide-angle image mosaics taken by the Mars Orbiter Camera (MOC) on the Mars Global Surveyor (MGS) at 2 p.m. local solar time, the MARCI maps will be used to track motions of clouds. Michael Malin is the principal investigator of both the Context Imager and MARCI, as well as MOC. The mission's HiRISE camera showed unprecedented detail in orbital images of Mars right off the bat with the above-mentioned image of Opportunity at Victoria Crater. This camera, however, imaged 64 areas on Mars during the week of testing. The images are "truly beautiful," Alfred McEwen, of the University of Arizona, the instrument's principal investigator, said at the press conference. "And since they resolve features the size of people, you can visualize yourself hiking around in these diverse terrains." HiRISE -- as well as the imaging spectrometer, and the orbiter's wider-looking Context Camera -- each observed Mawrth Vallis. Details visible in the new observations, such as small channels, are consistent with the theory about past wet conditions, McEwen noted. Another target was an unnamed southern crater that shows relatively young gullies, like those seen in many Mars locations viewed by the MGS orbiter. Braided channels characteristic of sediment-rich streams are visible in the new observations, reinforcing the interpretation that these geologically young gullies formed at least in part from erosion by flowing water. Malin was the first to discover the many geologically young gullies on Martian slopes. "We have a lot of Mars record and history to see here," Zurek told the crowd at DPS. "And we're going to have to learn to deal with all this data." He wasn't kidding. A kind of data tsunami is about to strike. Remember, this is the mission that promised to return more data than all other Mars missions combined. The sheer volume of data will be staggering. The MRO team at JPL, of course, will have help. Actually, the data from each instrument is downlinked straight to its home base -- the HiRISE data, for example, goes to the University of Arizona and McEwen, in Tucson, while the data from MARCI and the Context Image Camera go to Malin at his Malin Space Science Systems in San Diego, and so on. Eventually, the data will stream out to dozens of universities and institutes around the country and the world, keeping professors and students alike busy for decades to come. For now, the spacecraft is pretty much "buttoned-up," said Zurek. However, the Mars Climate Sounder (MCS), whose website is hosted by The Planetary Society, and MARCI have been continuing to collect data through the superior conjunction, as Mars orbits behind the Sun as viewed from Earth. MRO will officially begin its primary science mission phase on November 7, according to the latest word out of JPL. And then, get ready to be further blown away. In the meantime, the HiRISE team has set up a pan/zoom viewer that allows for some pretty deep immersions, and is just plain cool to use. See: http://marsoweb.nas.nasa.gov/HiRISE/hirise_images. |
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