When you’re looking to buy a used car, the various dents, dings, rust spots and crinkles can tell as much about its history as its mechanical records – the key is being able to read and interpret them. Asteroids can be considered the used cars of our solar system – they’ve been bouncing around for millions of years, colliding with planets and each other and picking up dents that can reveal what they hit and when. The meteorite that crashed in Chelyabinsk, Russia, in 2013 is one such well-traveled space rock and a new way of studying its dents has revealed that it hit Earth before … and may have been part of the early massive impact that formed the Moon.
“Asteroids provide an alternative record of collisional events in the inner Solar System. Unlike planets, asteroids have been thermally quiescent (cold) since around 4500 Ma (millions of years ago). Therefore, any mineral ages younger than the end of parent body metamorphism should faithfully record impact-induced metamorphism.”
In a paper published in the journal Communications Earth & Environment, researcher from the University of Cambridge describe why asteroids don’t lie -- their surfaces are cold and static and retain their collision craters and dents, along with evidence of what caused them, for millions of years. Craig Walton of Cambridge’s Department of Earth Sciences department, who led the research, says in a press release this sounds like common sense but is actually a radical view among his peers.
“Meteorite impact ages are often controversial: our work shows that we need to draw on multiple lines of evidence to be more certain about impact histories – almost like investigating an ancient crime scene.”
Early studies of the Chelyabinsk meteorite using uranium-lead dating, which looks at the time elapsed for one isotope to decay to another, show two major impacts -- one roughly 4.5 billion years ago and another within the last 50 million years. However, smaller impacts and age make exact figures difficult to determine. To fix that, the new study looked at how phosphate minerals inside the meteorite were shattered and how collision-induced heat affected their crystal structures. Depending on the changes in the minerals, the collisions could be put on a more accurate timeline.
The change in the minerals also can determine the size of the impact that affected them. The team found that the impact of 50 million years ago was probably a minor collision that knocked the Chelyabinsk meteorite off its host asteroid and sent it to Earth like a multi-car collision. The 4.5-billion-year old impact dent is more interesting because this occurred about the time some scientists estimate a small planet collided with Earth and formed the Moon. Research on other asteroids shows similar impact evidence between 4.48 – 4.44 billion years ago – making this a chaotic time.
“The fact that all of these asteroids record intense melting at this time might indicate Solar System re-organization, either resulting from the Earth-Moon formation or perhaps the orbital movements of giant planets.”
Will this new evidence convince skeptics that the Chelyabinsk meteorite was once part of a bigger space rock that formed the Moon? They’ll undoubtedly need more evidence.
Would you buy a banged-up used meteorite or wait for the new models to come out?