Wednesday, September 22, 2010

NASA's LRO Exposes Moon's Complex, Turbulent Youth

The moon was bombarded by two distinct populations of asteroids or comets in its youth, and its surface is more complex than previously thought, according to new results from NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft featured in three papers appearing in the Sept. 17 issue of Science.

In the first paper, lead author James Head of Brown University in Providence, R.I., describes results obtained from a detailed global topographic map of the moon created using LRO's Lunar Orbiter Laser Altimeter (LOLA). "Our new LRO LOLA dataset shows that the older highland impactor population can be clearly distinguished from the younger population in the lunar 'maria' -- giant impact basins filled with solidified lava flows," says Head. "The highlands have a greater density of large craters compared to smaller ones, implying that the earlier population of impactors had a proportionally greater number of large fragments than the population that characterized later lunar history."

Meteorite impacts can radically alter the history of a planet. The moon, Mars, and Mercury all bear scars of ancient craters hundreds or even thousands of miles across. If Earth was subjected to this assault as well -- and there's no reason to assume our planet was spared -- these enormous impacts could have disrupted the initial origin of life. Large impacts that occurred later appear to have altered life's evolution. The approximately 110-mile-diameter, partially buried crater at Chicxulub, in the Yucatan Peninsula of Mexico, is from an impact about 65 million years ago that is now widely believed to have led or contributed to the demise of the dinosaurs and many other lifeforms.

Scientists trying to reconstruct the meteorite bombardment history of Earth face difficulty because impact craters are eroded by wind and water, or destroyed by the action of plate tectonics, the gradual movement and recycling of the Earth's crust. However, a rich record of craters is preserved on the moon, because it has only an extremely thin atmosphere – a vacuum better than those typically used for experiments in laboratories on Earth. The moon’s surface has no liquid water and no plate tectonics. The only source of significant erosion is other impacts.

"The moon is thus analogous to a Rosetta stone for understanding the bombardment history of the Earth," said Head. "Like the Rosetta stone, the lunar record can be used to translate the 'hieroglyphics' of the poorly preserved impact record on Earth."

Tuesday, September 07, 2010

The Moon Puts on Camo

A new geologic map of the moon's Schrödinger basin paints an instant, camouflage-colored portrait of what a mash-up the moon's surface is after eons of violent events. The geologic record at Schrödinger is still relatively fresh because the basin is only about 3.8 billion years old; this makes it the moon's second-youngest large basin (it's roughly 320 kilometers, or 200 miles, in diameter).

This detailed geologic map of Schrödinger basin, which formed when a huge object struck the moon, reveals a patchwork of lunar material, including the peak ring (inner brown ring), recent volcanic activity (red), cratering (yellow) and plains material (dark green and kelly green). Credit: NASA/Scott Mest

Schrödinger is located near the moon's south pole, a region where pockets of permanent ice are thought to exist. The map will help researchers understand lunar geologic history and identify suitable landing sites for future exploration. Scott Mest, a research scientist with the Planetary Science Institute working at NASA's Goddard Space Flight Center in Greenbelt, Md., and his colleagues created this geologic map -- the most detailed one to date -- by combining topographic data from the Lunar Orbiter Laser Altimeter, a Goddard instrument aboard the 2009 Lunar Reconnaissance Orbiter, with images and spectral data from the earlier Clementine and Lunar Prospector missions.

Schrödinger is an example of an intriguing type of basin called a peak-ring. Like the basin rim (brown outer ring), the smaller and more fragmented peak ring (brown inner ring) is a mountainous region of crust that rose up after a huge object, probably measuring 35-40 kilometers, or about 21-25 miles, smacked into the moon here. These areas of raised crust are the oldest rocks in the basin and just about the only material that wasn't melted by the heat from the object's impact. The melted material was spewed in all directions and formed the plains. Patches of plains material can have slightly different textures and albedo (indicated by dark green and kelly green), probably because they cooled at different times. Fractures (black lines) formed in the basin floor as the material cooled.