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Where water came from is a longstanding mystery, with there being much debate on the subject. Many scientists believe water was delivered to Earth on meteors which were once part of a larger celestial body.
However, this theory has been hard to prove as the meteorites which were studied fell to Earth hundreds of millions of years ago.
As a result, these space rocks no longer contain water.
However, new research has looked at carbonaceous chondrite (CC) meteorites which fell to Earth in just the last century.
CC meteorites formed approximately 4.5 billion years ago when the solar system was just coming to be and were once part of a larger asteroid.
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The new research analysed the uranium and thorium distribution in said meteorites.
Uranium is water soluble while thorium is not, so if water existed on these meteorites, the evidence would be in the distribution of the elements as they melted.
In nine of the meteorites the team studied, the researchers found the evidence they were looking for, according to the research published in the journal Science.
However, both elements have relatively short half-lives, so the water movement on the rocks would have happened within the last few millions of years.
Nonetheless, it is a good indicator and adds weight to the theory that water, or at least the elements for it, were delivered to Earth on meteorites.
The research paper said: “Carbonaceous chondritic meteorites are thought to be fragments broken off parent bodies that orbit in the outer Solar System, largely unaltered since their formation.
“These meteorites contain evidence of reactions with liquid water that was thought to have been lost or completely frozen billions of years ago.
“Because this signature disappears after several half-lives of the radioactive isotopes, the meteorites must have been exposed to liquid within the past million years.
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“Fluid flow occurred after melting of ice, potentially by impact heating, solar heating, or atmospheric ablation.
“We favour the impact heating hypothesis, which implies that the parent bodies still contain ice.”
The team add that not only was water delivered from space in Earth’s ancient history but that it is continuing to do so.
They believe this idea could be tested by analysing asteroid samples which are returning to Earth, such as the Japanese space agency’s recent mission which collected samples from the asteroid Ryugu.
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