A major new study has found that the number of asteroids colliding with the Earth and its moon is three times higher than the rate 290 million years ago.
Traditionally, scientists have studied craters on Earth and studied the rocks around them to determine the rate of asteroid collision. However, this method may have a serious drawback. Numerous experts assert that this method is unreliable as older craters are worn away due to erosion and other geological processes.
Luckily, researchers have found this problem can be overcome by studying craters on the moon. Both the Earth and its moon are hit in the same proportions over time. Furthermore, the moon does not undergo processes like plate tectonics which degrade craters.
“The only obstacle to doing this has been finding an accurate way to date large craters on the moon”, said William Bottke, an asteroid expert at the Southwest Research Institute in Boulder, Colorado and a co-author of the paper.
The team studied the surface of the moon using thermal data and images collected by NASA’s Lunar Reconnaissance Orbiter (LRO), to determine the ages of the lunar craters. The NASA spacecraft’s thermal radiometer, known as Diviner, showed the scientists how heat is radiating off the moon’s surface — with larger rocks giving off more heat than finer, lunar soil. Paper co-author Rebecca Ghent, a planetary scientist at the University of Toronto and the Planetary Science Institute in Tucson, Arizona, calculated the rate at which moon rocks break down into soil, and revealed a relationship between the amount of large rocks near a crater and the crater’s age. Using Ghent’s technique, the team compiled the ages of all lunar craters younger than about a billion years.
It was found that younger craters tend to be covered by more boulders and rocks than smaller craters. This happens because the boulders ejected by an asteroid strike get ground down over hundreds of millions of years by a constant rain of tiny meteorites.
A comparison of the numbers and ages of craters on the moon and the Earth showed that they are remarkably similar. This presented a challenge to the theory that Earth had lost many of its craters. However, according to Bottke, this shows that the Earth has fewer older craters on its most stable regions not because of erosion, but because the impact rate was lower prior to 290 million years ago.
Thus far, it is not clear what caused such a drastic jump in the rate of asteroid collision. The researchers have hypothesized that it may be related to large collisions taking place more than 290 million years ago in the main asteroid belt between the orbits of Mars and Jupiter. Such events can create debris that could reach our solar system.
“It’s perhaps fair to say it was a date with destiny for the dinosaurs–their downfall was somewhat inevitable given the surge of large space rocks colliding with Earth”, concluded Dr Thomas Gernon, Associate Professor at the University of Southhampton and co-author in the study.
These findings have been published in Science.