The moon rocks brought back by the Apollo astronauts have been in an almost constant state of investigation since they arrived on Earth, investigation which – when combined with studies into howardite and eucrite meteorites – have led NASA scientists to conclude that our moon has a lot more in common with asteroids located in our Solar System’s asteroid belt than previously understood.
Scientists from NASA’s Lunar Science Institute (NLSI) in Moffett Field, California, have discovered that the same population of high-speed projectiles that made contact with our moon approximately four billion years ago also hit the asteroid Vesta, as well as maybe other asteroids.
The findings support the theory that the repositioning of gas giants Jupiter and Saturn from their original orbits to their current locations had a destabilising effect on portions of the asteroid belt, which subsequently triggered what has come to be known as the lunar cataclysm, or the Late Heavy Bombardment, a massive bombardment of asteroids that took place an estimated 4.1 to 3.8 billion years ago which left our moon scarred by numerous impact craters. The new research subsequently goes a long way to verifying the theory, as well as further expanding our understanding of the event; shedding light on the start and duration of the lunar cataclysm, as well as proving that it affected more than just the inner system planets.
“It’s always intriguing when interdisciplinary research changes the way we understand the history of our solar system,” said Yvonne Pendleton, NLSI director. “Although the moon is located far from Vesta, which is in the main asteroid belt between the orbits of Mars and Jupiter, they seem to share some of the same bombardment history.”
Scientists have now discovered that studying meteorites from the giant asteroid Vesta helps them understand the event known as the “lunar cataclysm,” when a repositioning of the gas giant planets destabilized a portion of the asteroid belt and triggered a solar-system-wide bombardment.
Image Credit – NASA/GSFC/ASU/JPL-Caltech/UCLA/MPS/DLR/IDA
While the moon rocks brought back by the Apollo astronauts are obvious contributors to the research, less well-known are the meteorite samples which were used to study the collisional history of the main belt asteroids. Known as howardite and eucrite meteorites – a common type of asteroid found on Earth – they are believed to all derive from the second most-massive asteroid in the Solar System; Vesta (or 4 Vesta by its minor-planet designation). Located in the asteroid belt which rings the Solar System between Mars and Jupiter, Vesta is estimated to comprise 9% of the mass of the entire asteroid belt. Howardite and eucrite meteorites allow scientists the rare opportunity of studying Vesta, allowing for discoveries such as its similarities to the Moon.
In addition to studying the howardite and eucrite meteorites here on Earth, NASA scientists used the latest dynamical models of early main belt evolution, and studied close-in observations of Vesta’s surface taken by NASA’s Dawn spacecraft, a robotic vessel tasked with studying Vesta and Ceres, the two largest members of our Solar System’s asteroid belt. Dawn reached Vesta on July 16, 2011, and spent over a year studying the asteroid. It is currently en route to Ceres, which it is scheduled to reach in February 2015.
Using dynamical models of early main belt evolution, the scientists were able to discover the likely source of the high velocity impacts that were detected on Vesta. The same projectiles that hit Vesta were believed to have had orbits that would have also enabled them to strike the moon at high speeds.
“It appears that the asteroidal meteorites show signs of the asteroid belt losing a lot of mass four billion years ago, with the escaped mass beating up on both the surviving main belt asteroids and the moon at high speeds” says lead author Simone Marchi, who has a joint appointment between two of NASA’s Lunar Science Institutes, one at the Southwest Research Institute in Boulder, Colo., and another at the Lunar and Planetary Institute in Houston. “Our research not only supports the current theory, but it takes it to the next level of understanding.”
Personally, that ‘next level of understanding’ is tantalisingly close.