Scientists Detect Dramatic Shift in the Energy of Impacting Asteroids that Pummeled the Ancient Earth and Moon
Simone Marchi , an NLSI Postdoctoral Fellow, William F. Bottke , the NLSI Principal Investigator at Southwest Research Institute, David A. Kring , the NLSI Principal Investigator at USRA's Lunar and Planetary Institute, and Allessandro Morbidelli , Observatoire de la Cote d'Azur, France, measured the sizes of the most ancient impact craters on the Moon and discovered a pattern that indicates the energy of impacts associated with the formation of immense 300 to >1000 kilometer diameter impact basins increased for the youngest ones. They interpret that pattern to indicate an increase in impact velocities generated by the movement of Jupiter and other outer solar system planets.
"We are very proud of Dr. Kring's lunar science research," said USRA Vice President of Science, Dr. Don Kniffen, "This is an outstanding example of the type of collaborative scientific investigations that are critical to expanding our knowledge of the history of our solar system - an important part of USRA's mission."
The team has been testing the lunar cataclysm hypothesis, which suggests the Earth and Moon were severely bombarded by a brief pulse of impacting objects that flooded the inner solar system about 4 billion years ago. Testing that hypothesis and determining the magnitude and duration of any impact cataclysm is the top science priority for future exploration of the Moon according to a previously published report by the National Research Council. The concept of an impact cataclysm has its roots in the Apollo missions to the Moon, when astronauts collected rock samples that are dominated by impact-reset ages of 3.9 to 4.0 billion years. If that type of bombardment occurred, the authors wondered, can details of it be unraveled from the imprint it made on the lunar surface?
Dr. Kring, USRA Senior Staff Scientist, noted, "The bombardment of asteroids was an exciting event in solar system history. It reshaped the surfaces of the Earth and Moon at virtually the same time that life was emerging nearly 4 billion years ago."
Detailed mapping by the United States Geological Survey previously identified small regions of the lunar surface that are incredibly ancient and that might preserve clues about the bombardment. Using new data obtained from the Lunar Orbiter Laser Altimeter, which is an instrument on NASA's Lunar Reconnaissance Orbiter and currently in orbit around the Moon, the team re-studied those ancient surfaces and measured the sizes of the impact craters on them. They detected a subtle shift in those crater sizes that can best be explained by an increase in the velocities of the asteroids that produced them. The increase in velocity seems to occur after the Moon's largest impact basin was produced, the 2,500 kilometer diameter South Pole-Aitken Basin, and before the formation of the Nectaris Basin, which is near the Apollo 16 landing site.
These results indicate some of the oldest impact basins produced on the Moon were not part of the lunar cataclysm. They also indicate, however, that the largest impact basins on the lunar nearside, visible from backyards around the world, were produced after the giant planets moved and the velocities of impacting asteroids doubled. This doubling of velocity is consistent with computer models that suggest a dramatic shift in the configuration of outer solar system planets to their present positions roughly four billion years ago.
The NLSI is a virtual organization that enables collaborative, interdisciplinary research in support of NASA lunar science programs. The institute uses technology to bring scientists together around the world and comprises competitively selected U.S. teams and several international partners. NASA's Science Mission Directorate and the Exploration Systems Mission Directorate at the agency's Headquarters in Washington, funds the institute, which is managed by Ames.
Universities Space Research Association (USRA) is an independent, nonprofit research corporation where the combined efforts of in-house talent and university-based expertise merge to advance space science and technology. USRA works across disciplines including biomedicine, astrophysics, and engineering and integrates those competencies into applications ranging from fundamental research to facility management and operations. USRA engages the creativity and authoritative expertise of the research community to develop and deliver sophisticated, forward-looking solutions to Federal agencies and other customers - on schedule and within budget.