Our Moon was born after a young Earth smashed its twin Theia, scientists writing in three studies just published by Nature have suggested. Their intriguing evidence reveals the Moon’s origins may have been more incestuous than previously thought.
Since the 1980s, scientists studying the Moon have largely agreed on the “giant impact” paradigm, in which a wandering planet, dubbed Theia, came from far, far away, and crashed into Earth about 4.5 billion years ago. The impact destroyed Theia, which was about the size of Mars, and the Moon was largely formed by the debris that remained orbiting Earth.
However, a new paper from the Israel Institute of Technology and Nice University in France suggests that theory may need some rethinking.
The planets in our Solar System have radically different chemical makeups, so you’d expect the Theia-formed Moon to reflect that. Instead, the Moon is made up of stuff remarkably similar to the material that makes up Earth.
“It turns out that an impactor is not similar to any other random body in the solar system. The Earth and Theia appear to have shared much more similar environments during their growth than just any two unrelated bodies,” said Dr Alessandra Mastrobuono-Battisti.
“In other words, Theia and Earth were formed in the same region, and have therefore collected similar material. These similar living environments also led them eventually to collide; and the material ejected mostly from Theia, ultimately formed the Moon. Our results reconcile what has been perceived as a contradiction between the process whereby Moons are formed (from matter from the impacting body) and the similarity between Earth and the Moon.”
To come to this conclusion, the team ran intensive computer simulations of late-stage planetary formations. While there are wandering planets that can cause impact, they found that in between 20 and 40 per cent of cases the impacting planet was formed in the same orbital sphere as its victim.
The research is backed by a chemical analysis of tungsten in Moon rocks collected by the Apollo missions, carried out by the University of Maryland. The team found that both bodies contained remarkably similar amounts of Tungsten-182, although the Earth has slightly less of it.
“The small, but significant, difference in the Tungsten isotopic composition between Earth and the Moon perfectly corresponds to the different amounts of material gathered by Earth and the Moon post-impact,” said Richard Walker, a professor of geology at UMD and co-author of the study. “This means that, right after the Moon formed, it had exactly the same isotopic composition as Earth’s mantle.”
This is supported by a similar study of Moon rock carried out by Thomas Kruijer of the University of Münster in Germany and Mathieu Touboul at the University of Lyon in France, which pegged the difference in tungsten in the Earth and the Moon to 20 to 27 parts per million.
The team posits that the difference can be accounted for by the Earth’s larger size: it will attract more meteorites and comets that change our world’s chemical composition slightly when they hit the ground.
“This result brings us one step closer to understanding the close familial relationship between Earth and the Moon,” Walker said. “We still need to work out the details, but it’s clear that our early solar system was a very violent place.”
( Via www.theregister.co.uk )