Lunar scientists shed light on Moon's impact history

February 28th, 2012 in Astronomy & Space / Space Exploration
Post Lunar Cataclysm diagram of our Solar System. Credit: LPI/Marchi/Bottke/Kring/Morbidelli.


(PhysOrg.com) -- A team of researchers from the NASA Lunar Science Institute (NLSI) at NASA Ames Research Center, Moffett Field, Calif., have discovered that debris that caused a "lunar cataclysm" on the moon 4 billion years ago struck it at much higher speeds than those that made the most ancient craters. The scientists found evidence supporting this scenario by examining the history of crater formation on the moon.

During Earth's earliest days, our planet and others in the inner , including the moon, experienced repeated impacts from debris that formed the building blocks of the planets. Over time, as material was swept up and incorporated into the , the rate of impacts decreased. Then, roughly 4 billion years ago, a second wave of impacts appears to have taken place, with projectiles hitting at much higher speeds. This increase could reflect the origin of the debris, where main belt asteroids were dislodged and sent into the by shifts in the orbits of the giant planets.




Determining the magnitude and duration of any impact cataclysm and testing that hypothesis is a top science priority for future exploration of the moon, according to a previously published report by the National Research Council.

When Apollo astronauts gathered rock samples from the moon, many samples had ages dating back 3.9 to 4 billion years ago, suggesting an enhanced pulse of bombardment. If a bombardment of asteroids hit the moon as theorized, there could be indicators left on the lunar surface that would help validate the theory. Detailed mapping by the United States Geological Survey has previously identified small regions of the lunar surface that might contain clues about the bombardment. The team re-studied those ancient surfaces and measured the sizes of the impact craters using new data obtained from the Lunar Orbiter Laser Altimeter, an instrument on NASA’s Lunar Reconnaissance Orbiter (LRO) currently orbiting around the moon.


The inferred increase in velocity seems to have occurred after the moon’s largest impact basin was produced, the 2,500-kilometer-diameter South Pole-Aitken Basin, but before the formation of the largest lava-filled impact basins on the lunar nearside, visible from backyards around the world.

“It is fascinating that the surface of our own records evidence of orbital changes in Jupiter and Saturn that took place so long ago,” said NLSI Director Yvonne Pendleton.

More information: lunarscience.arc.nasa.gov/

Provided by JPL/NASA

"Lunar scientists shed light on Moon's impact history." February 28th, 2012. http://phys.org/news/2012-02-lunar-scientists-moon-impact-history.html