Scientist searches for moons around asteroids

ScienceDaily (Oct. 7, 2011) — Most people know that some planets have moons but would be surprised to know that some asteroids do, too. According to Joshua Emery, assistant professor of earth and planetary sciences at the University of Tennessee, Knoxville, about 20 percent of them do.

Emery is part of an international team of planetary astronomers, led by Franck Marchis of the Carl Sagan Center of the SETI Institute in Mountain View, Calif., searching for moons around asteroids. The discovery of moons around asteroids is important because it can provide clues to the asteroid's formation.

Emery and his team's research has focused on the triple asteroid Minerva, the fourth asteroid located in the main-belt -- which houses most of the solar system's asteroids -- known to possess two moons.

"Minerva was thought to be a pretty typical, unremarkable asteroid until we discovered its two moons," said Emery. "Now, interest in this system has grown, and through a lot of new observations from both ground-based and space-based telescopes, we have developed a much more detailed understanding of Minerva and its moons."

The team studied the asteroid in detail using the large W.M. Keck telescope in Hawaii and a small robotic telescope at Kitt Peak in Arizona. By piecing together old and new observations, the astronomers were able to make precise determinations of the moons' orbits. With shape, size, and mass in hand, the scientists then derived the asteroid's density -- determining that Minerva is different than the other large asteroids in the main-belt.

"All other large main-belt asteroids with one or more moons are very porous," said Emery. "Such high porosity strongly suggests that they are piles of rubble held together by gravity rather than solid rocks. Imagine an asteroid being completely blasted apart in a collision, then the pieces coalescing back together--this is how we think most of these large, multiple asteroid systems form. From these glimpses into the interior structure of asteroids, we gain insight not only into the history and formation of multiple asteroid systems, but also the structure and origin of asteroids in general."

The results of the group's findings were released at the EPSC-DPS meeting in Nantes, France. Other members of the international team of planetary astronomers are J.E. Enriquez, of Carl Sagan Center at the SETI Institute, Calif.; P. Descamps, J. Berthier, and F. Vachier of the Institut de Mecanique Celeste et de Calcul des Ephemerides, France; J. Durech of Charles University, Prague, Czech republic; P. Dalba, UC Berkeley, Calif.; A.W. Harris of DLR, Berlin, Germany; J. Melbourne of Caltech, Pasadena, Calif.; A.N. Stockton and T.J. Dupuy of the University of Hawaii, Honolulu; and C.D. Fassnacht of the University of California at Davis, Calif.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Tennessee at Knoxville, via EurekAlert!, a service of AAAS.

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Scientist searches for moons around asteroids

ScienceDaily (Oct. 7, 2011) — Most people know that some planets have moons but would be surprised to know that some asteroids do, too. According to Joshua Emery, assistant professor of earth and planetary sciences at the University of Tennessee, Knoxville, about 20 percent of them do.

Emery is part of an international team of planetary astronomers, led by Franck Marchis of the Carl Sagan Center of the SETI Institute in Mountain View, Calif., searching for moons around asteroids. The discovery of moons around asteroids is important because it can provide clues to the asteroid's formation.

Emery and his team's research has focused on the triple asteroid Minerva, the fourth asteroid located in the main-belt -- which houses most of the solar system's asteroids -- known to possess two moons.

"Minerva was thought to be a pretty typical, unremarkable asteroid until we discovered its two moons," said Emery. "Now, interest in this system has grown, and through a lot of new observations from both ground-based and space-based telescopes, we have developed a much more detailed understanding of Minerva and its moons."

The team studied the asteroid in detail using the large W.M. Keck telescope in Hawaii and a small robotic telescope at Kitt Peak in Arizona. By piecing together old and new observations, the astronomers were able to make precise determinations of the moons' orbits. With shape, size, and mass in hand, the scientists then derived the asteroid's density -- determining that Minerva is different than the other large asteroids in the main-belt.

"All other large main-belt asteroids with one or more moons are very porous," said Emery. "Such high porosity strongly suggests that they are piles of rubble held together by gravity rather than solid rocks. Imagine an asteroid being completely blasted apart in a collision, then the pieces coalescing back together--this is how we think most of these large, multiple asteroid systems form. From these glimpses into the interior structure of asteroids, we gain insight not only into the history and formation of multiple asteroid systems, but also the structure and origin of asteroids in general."

The results of the group's findings were released at the EPSC-DPS meeting in Nantes, France. Other members of the international team of planetary astronomers are J.E. Enriquez, of Carl Sagan Center at the SETI Institute, Calif.; P. Descamps, J. Berthier, and F. Vachier of the Institut de Mecanique Celeste et de Calcul des Ephemerides, France; J. Durech of Charles University, Prague, Czech republic; P. Dalba, UC Berkeley, Calif.; A.W. Harris of DLR, Berlin, Germany; J. Melbourne of Caltech, Pasadena, Calif.; A.N. Stockton and T.J. Dupuy of the University of Hawaii, Honolulu; and C.D. Fassnacht of the University of California at Davis, Calif.

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Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Moon's rough 'wrinkles' reveal clues to its past

ScienceDaily (May 15, 2011) — Written on the moon's weary face are the damages it has endured for the past 4-1/2 billion years. From impact craters to the dark plains of maria left behind by volcanic eruptions, the scars are all that remain to tell the tale of what happened to the moon. But they only hint at the processes that once acted -- and act today -- to shape the surface.

To get more insight into those processes, Meg Rosenburg and her colleagues at the California Institute of Technology, Pasadena, Calif. put together the first comprehensive set of maps revealing the slopes and roughness of the moon's surface. These maps are based on detailed data collected by the Lunar Orbiter Laser Altimeter (LOLA) on NASA's Lunar Reconnaissance Orbiter. LOLA and LRO were built at NASA's Goddard Space Flight Center in Greenbelt, Md.

Like wrinkles on skin, the roughness of craters and other features on the moon's surface can reveal their age. "The key is to look at the roughness at both long and short scales," says Rosenburg, who is the first author on the paper describing the results, published in the Journal of Geophysical Research earlier this year.

The roughness depends on the subtle ups and downs of the landscape, a quality that the researchers get at by measuring the slope at locations all over the surface. To put together a complete picture, the researchers looked at roughness at a range of different scales -- the distances between two points -- from 17 meters (about 56 feet) to as much as 2.7 kilometers (about 1.6 miles).

"Old and young craters have different roughness properties -- they are rougher on some scales and smoother on others," says Rosenburg. That's because the older craters have been pummeled for eons by meteorites that pit and mar the site of the original impact, changing the original shape of the crater.

"Because this softening of the terrain hasn't happened at the new impact sites, the youngest craters immediately stand out," says NASA Goddard's Gregory Neumann, a co-investigator on LOLA.

"It is remarkable that the moon exhibits a great range of topographic character: on the extremes, surfaces roughened by the accumulation of craters over billions of years can be near regions smoothed and resurfaced by more recent mare volcanism," says Oded Aharonson, Rosenburg's advisor at the California Institute of Technology.

By looking at where and how the roughness changes, the researchers can get important clues about the processes that shaped the moon. A roughness map of the material surrounding Orientale basin, for example, reveals subtle differences in the ejecta, or debris, that was thrown out when the crater was formed by a giant object slamming into the moon.

That information can be combined with a contour map that shows where the high and low points are. "By looking at both together, we can say that one part of Orientale is not just higher or lower, it's also differently rough," Rosenburg says. "That gives us some clues about the impact process that launched the ejecta and also about the surface processes that later acted to modify it."

Likewise, the smooth plains of maria, which were created by volcanic activity, have a different roughness "signature" from the moon's highlands, reflecting the vastly different origins of the two terrains. Maria is Latin for "seas," and they got that name from early astronomers who mistook them for actual seas.

Just as on the moon, the same approach can be used to study surface processes on other bodies as well, Rosenburg says. "The processes at work are different on Mars than they are on an asteroid, but they each leave a signature in the topography for us to interpret. By studying roughness at different scales, we can begin to understand how our nearest neighbors came to look the way they do."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Goddard Space Flight Center.

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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