New study uses meteorites to date moon-forming impact

Meteorite PAT 91501 was melted by impact in the asteroid belt 4.460 billion years ago. Credit: NASA.

Not too long after the planets began forming, a Mars-sized object slammed into Earth, creating the debris that would later coalesce into the moon. Some of the debris from this giant impact escaped all the way out to the asteroid belt. Collisions there left shock-heating signatures – a permanent record of the impact event – that can still be detected billions of years later in meteorites that have fallen to Earth.

Planetary scientists, including Professor Ed Scott at UH Mānoa’s Hawai‘i Institute for Geophysics and Planetology, have found that a significant number of these altered meteorites have ages clustering at 100 million years after the solar system’s birth — the true age of the moon-forming impact, they say. The result is an independent check on other estimates for the moon’s age, and it suggests that the asteroid belt can provide important clues to the timing and nature of major events in the inner solar system when planets were forming. The team’s work appears in the current issue of the journal Science.

“Meteorites provide an extraordinary record of major events in the formation of the planets and the solar system,” said Scott. “We study meteorites and asteroids as they provide the key to understanding how and when planets formed.”

The team of NASA-funded researchers modeled the evolution of giant impact debris and analyzed ancient impact heating signatures in stony meteorites to conclude that pieces from the giant impact did indeed strike the asteroid belt.

Subsequent, less violent collisions between asteroids have since ejected some shocked remnants back to Earth in the form of fist-sized meteorites. By determining the age of the shock signatures in those meteorites, scientists were able to infer that their origin likely corresponds to the time of the giant impact, and therefore to the age of the Moon.

Noted Director of NASA’s Solar System Exploration Research Virtual Institute (SSERVI) Yvonne Pendleton, “This is an excellent example of the power of multidisciplinary science. By linking studies of the Moon, of main belt asteroids, and of meteorites that fall to Earth, we gain a better understanding of the earliest history of our Solar System.”

“It is even possible that tiny remnants of the Moon-forming impactor or proto-Earth might still be found within meteorites that show signs of shock heating by giant impact debris. This would allow scientists to explore for the first time the unknown primordial nature of our home world,” said lead author of the paper and Principal Investigator Bill Bottke of the Institute for the Science of Exploring Targets team at the Southwest Research Institute, a U.S. team member of SSERVI.

SSERVI is funded by the Science Mission Directorate and Human Exploration and Operations Mission Directorate at NASA Headquarters to enable cross-team and interdisciplinary research that pushes forward the boundaries of science and exploration.

The abstract of the paper may be found here.

Additional media resources to accompany this release are available from the Southwest Research Institute at:

For more information on how the moon may have formed in the giant impact, visit

Complete photo caption:
This meteorite, called PAT 91501,with black vesicles, was recovered from Antarctica. It was melted by a high velocity impact 4.460 billion years ago in the asteroid belt beyond Mars’ orbit. The body that slammed into the parent body of this meteorite could have been created during the giant impact that formed the Moon. If so, the age of this meteorite and others like it may provide important clues to the age of the Moon.

Scale cube is 1 cm wide. Photo courtesy of NASA Johnson Space Center. The meteorite was dated by Gretchen Benedix-Bland (PhD UH Manoa, 1997) and her colleagues (see Geochimica et Cosmochimica Acta vol. 72, pages 2417–2428, 2008).