Some meteorites that fell to Earth relatively recently may have contained liquid water within the past million years. This means that space rocks might have delivered water to our planet’s surface throughout its history rather than just very early on.
Many scientists suspect that meteorites once brought water to Earth. But previous analysis of the rocks suggested that the chemical reactions inside them that involve liquid water ceased billions of years ago. So it seemed possible they lost their water long ago.
Simon Turner at Macquarie University in Sydney, Australia, and his colleagues analysed nine meteorites that fell to Earth within the past century. These meteorites were once part of asteroids that formed about 4.5 billion years ago.
When ice in a meteorite melts, the water and fluid soluble elements move from one part of the rock to another, says Turner. Because uranium is water-soluble and thorium isn’t, the researchers could look for evidence of water by looking at the distribution of uranium and thorium isotopes. “Uranium and thorium have very short half-lives and so only record events that happened within the last 1 million years,” says Turner. The pattern of uranium and thorium suggested that the meteorites were experiencing chemical reactions involving liquid water within the past million years, he says.
“We are used to thinking of meteorites from asteroids as being unchanged since the early solar system,” says Sara Russell at the Natural History Museum in London, who wasn’t involved in the research. The new study suggests they have remained chemically active. These meteorites may have continued to supply water and organic compounds to Earth in the recent past. The idea could be tested by analysing samples taken directly from asteroids, says Russell, for instance by Japan’s Hayabusa 2 spacecraft and NASA’s OSIRIS-REx spacecraft.