Science NOW | 16 Sept 2010
Moon’s craters give new clues to early solar system bombardmentThe moon may be only 384,000 kilometers away, but that doesn't mean it isn't full of mystery. Scientists studying the first year's worth of data from NASA's Lunar Reconnaissance Orbiter (LRO) have found unexpected mineral deposits, the possibility that our natural satellite was bombarded in two waves in its early history, and virtually no trace of a pristine lunar surface. If scientists can confirm these findings, they could take big steps toward understanding not only the moon's distant past but also Earth's and the rest of the solar system's as well.
In a news briefing held online today, in conjunction with three papers published in Science, researchers presented a tantalizing preliminary portrait of what the moon must have endured during its early history, ending around 3.5 billion years ago. LRO's Lunar Orbiter Laser Altimeter (LOLA), which can determine the height of a small patch of lunar soil to within 10 centimeters, has enabled scientists to compile a detailed topographical map of 5185 lunar craters, all more than 20 kilometers in diameter.
Planetary geologist James Head III of Brown University told reporters that the LOLA data on the moon's impact history support an emerging idea about early bombardment in the solar system. By analyzing the topographical map, the researchers could determine when objects struck existing craters, and they could measure the size of the objects. The data suggest that larger objects tended to hit the moon earlier in its history than did smaller objects. There seemed to be two stages of impacts, he said, and they were "distinctly different." That's an important clue, he added, about what was going on in the early solar system—including on Earth—because "the same population [of objects] that was hitting the moon certainly was hitting the Earth." Why the moon took such big hits early on isn’t clear.
Planetary scientist Benjamin Greenhagen of NASA's Jet Propulsion Laboratory in Pasadena, California, described a study he co-authored of lunar surface chemistry by LRO's Diviner Lunar Radiometer Experiment (DLRE), which analyzes chemical composition by reading the lunar soil's infrared emissions—its internal heat. He said this method gives a much more detailed picture than using the heat from reflected sunlight, the method used by previous studies, because each mineral emits a distinctive radiation signature. The Diviner survey has provided the first chemical map of the entire lunar surface, he added.
Based on the Diviner data, Greenhagen said the lunar orbiter has located five previously unobserved sites in the moon's highlands that are surprisingly rich in oxygen-bearing silicate minerals. As of now, the reason for the deposits is unknown, but the presence of oxygen in the lunar rock would make those sites attractive for future moon missions, even for human colonies, which could use the oxygen for breathing and as a rocket-fuel component.
Planetary scientist Timothy Glotch of Stony Brook University in New York said the DLRE data also revealed concentrations of what he called highly silicic minerals, such as quartz and feldspar. These minerals, which likely originated deep below the lunar surface, are different from anything found on the lunar surface before, so they raise the possibility of an as-yet-unknown geologic process at work.
Among the mysteries unearthed by Diviner is the apparent complete lack of pristine lunar mantle on the surface. The scientists had hoped to find spots on the moon containing material going back to its formation. But the instrument's surveys turned up no such evidence, even at surface locations considered to be the moon's oldest. Glotch said all of the new mineral discoveries should make for "some new, really juicy targets for future [lunar] exploration."
Brown University | 16 Sept 2010
Global Distribution of Large Lunar Craters: Implications for Resurfacing and Impactor Populations - JW Head et alA first-ever uniform, comprehensive catalog of large craters on the Moon is providing new clues to the bombardment history that characterized the chaotic early days of the inner solar system. In a paper that appears on the cover of Science, a research team led by Brown University identified and mapped more than 5,000 large craters, established the oldest regions on the Moon, and confirmed a theory about past solar system bombardment.
The Moon looks like a pockmarked golf ball. The dimples and divots on its surface are testament that our satellite has withstood a barrage of impacts from comets, asteroids and other space matter throughout much of its history. Because the geological record of that pummeling remains largely intact, scientists have leaned on the Moon to reconstruct the chaotic early days of the inner solar system.
Now a team led by Brown University planetary geologists has produced the first uniform, comprehensive catalog of large craters on the Moon that could shed light on the full-scale, planetary bombardment that characterized the inner solar system more than 4 billion years ago. In a paper appearing on the cover of Science, the team used data from the Lunar Orbiter Laser Altimeter, one of a suite of instruments aboard NASA’s Lunar Reconnaissance Orbiter, to identify and map 5,185 craters that are 20 kilometers in diameter or larger.
From the crater count and analysis, the team, which includes scientists from the Massachusetts Institute of Technology and the NASA Goddard Space Flight Center, determined the Moon’s oldest regions are the southern near side and the north-central far side. The group also confirmed that the South Pole–Aitken Basin is the oldest basin, meaning that any samples from there could be invaluable to further understanding the Moon and other bodies of the inner solar system.
- Science 329(5998) 1504 (17 Sep 2010) DOI: 10.1126/science.1195050
University of California, Los Angeles | 16 Sept 2010
Global Silicate Mineralogy of the Moon from the Diviner Lunar Radiometer - BT Greenhagen et alThe moon is more geologically complex than previously thought, scientists report Sept. 17 in two papers published in the journal Science.
Their conclusion is based on data from the Diviner Lunar Radiometer Experiment aboard NASA's Lunar Reconnaissance Orbiter (LRO), an unmanned mission to comprehensively map the entire moon. The spacecraft orbits some 31 miles above the moon's surface.
The new data reveal previously unseen compositional differences in the moon's crustal highlands and have confirmed the presence of material surprisingly abundant in silica — a compound containing the chemical elements silicon and oxygen — in five distinct lunar regions.
Every mineral, and therefore every rock, absorbs and emits energy with a unique spectral signature that can be measured to reveal its identity. For the first time ever, Diviner is providing scientists with global, high-resolution infrared maps of the moon, which are enabling them to make a definitive identification of silicates commonly found within its crust.
Co-authors on the research include David Paige, Diviner's principal investigator and a UCLA professor of planetary science; Benjamin Greenhagen, a scientist at NASA's Jet Propulsion Laboratory who earned his Ph.D. at UCLA under Paige; Timothy Glotch, an assistant professor of geosciences at New York's Stony Brook University; and Paul Hayne, who earned his Ph.D. at UCLA this year under Paige.
- Science 329(5998) 1507 (17 Sep 2010) DOI: 10.1126/science.1192196
Stony Brook University | 16 Sept 2010
Highly Silicic Compositions on the Moon - TD Glotch et alUsing data from the Diviner Lunar Radiometer, an instrument uniquely capable of identifying common lunar silicate minerals, scientists at Stony Brook University in New York and NASA’s Jet Propulsion Laboratory have found previously unseen compositional differences in the crustal highlands of the Moon, and have confirmed the presence of anomalously silica-rich material in five distinct regions.
“In layman’s terms, we have discovered a new and fundamentally different type of rock on the Moon,” declares Dr. Timothy Glotch, assistant professor in the Department of Geosciences at Stony Brook and lead author of one of two papers on the research in this week’s issue of Science. “For decades, we’ve recognized that these spots in the crustal highlands of the Moon are different. Now we have the evidence. The Moon is more geologically complex than previously thought, and we now have to refine our ideas about its formation.”
Every mineral, and therefore every rock, absorbs and emits energy with a unique spectral signature that can be measured to reveal its identity. For the first time, the Diviner Lunar Radiometer is providing scientists with global, high-resolution infrared maps of the Moon, which are enabling them to make a definitive identification of silicates commonly found within its crust.
- Science 329(5998) 1510 (17 Sep 2010) DOI: 10.1126/science.1192148
NASA GSFC | 10-082 | 16 Sept 2010
NASA JPL | 2010-303 | 16 Sept 2010
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