Meteorites that formed in the earliest days of the solar system may contain liquid water, according to new research, leading the theory that meteorites brought water and other precursors for life to our planet billions of years ago.
Carbonaceous chondrites are a special group of meteorites whose origins date back to the formation of the solar system. When bits of it are found on Earth, they turn out to contain tantalizing shreds of information, such as minerals that only appear in the presence of water and organic compounds such as amino acids – some of the building blocks of life.
As a result, carbonaceous chondrites have become an important candidate for how water got to Earth. A great way to know for sure would be if a chondrite – which, while rare among their fallen meteorite compatriots, still regularly impacts Earth – landed with water on it, and we were lucky enough to see the rock and restore it.
That is quite a task. The asteroid Ryugu was recently were found to be water dry long before Japan got there with its Hayabusa2 spacecraft. Until now, scientists were aware that fluid flow was happening on carbonaceous chondrites at some point, but they didn’t know how recently that flow might have happened. Previous dating methods showed that water was present on these rocks early – about 4.5 billion years ago, shortly after Earth was formed.
All of this leads to the hypothesis that every change, and every presence of water, was very old. So our test was to say, could there have been a young change? “ Simon Turner, an isotope geochemist at Macquarie University in Sydney, Australia, said in a video call. “That is to say, there is still ice on these meteorites.” Turner is lead author of a new paper describing fluid flow in carbonaceous chondrites, published this week in the journal Scientific Reports.
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A team of researchers from Macquarie University, Florida State University, and the Natural History Museum of Paris has discovered that these carbonaceous chondrites have had some amount of fluid over the past hundred thousand years – very recently, as far as space and geologic time scales go.
All meteorites fall, but only those witnessed to fall are thereafter called “falling.” Turner’s team only used carbonaceous chondrite drops in their research, because those fresh from outer space rocks have a clear timestamp of how they arrived and have a context for what they came into contact with on Earth (ie, what they may have been contaminated with). The meteorites included in the study came from all over: one came from Sutter’s Mill, where the California Gold Rush began, while another landed on a frozen lake in Russia, among many other locations around the world.
The research team took samples from these space rocks and dated their water flow with uranium-thorium dating, where isotopes of the two elements can be measured to distinguish age. In this case, the question was not the age of these meteorites themselves, but the age at which liquid moved in the rock. Uranium is very mobile in liquid, while thorium is not, so by seeing when the uranium was moving within the meteorite relative to the thorium, the team was able to deduce when the water was washing around.
“If there was ice on the bodies, and there was a reason why ice melted and moved, and it happened in the last million years, then you should expect different behavior of uranium and thorium,” Turner said.
In other words, when fluid flows, whether on a space rock or along a riverbed, it shifts isotopes around, leaving a short-term record of the flow. That signature disappears if too much time passes. If the isotopes moved within a million years, the team would detect that disturbance.
The recency of the liquid movement found in some of the team’s samples is exciting – it means carbonaceous chondrites may very well still contain ice, if they were to flow only a few hundred thousand years ago liquid.
Edward Young, a geochemist at UCLA who was not affiliated with the recent paper, said in an email that the new research was “very interesting” and “elegant.” He noticed the other Scientists recently took note of the widespread water flow on the asteroid Bennu, thanks to NASA’s ongoing OSIRIS-REx mission.
A next step would be to test space rocks that did not fall through Earth’s atmosphere like a fireball, a violent process that obscures exactly how the ice melted on these asteroids (samples brought by spacecraft would be helpful). Meanwhile, researchers will poke around the fallen space rocks and keep an eye on the skies for new evidence that could crash.