Moon And Earth Share A Common Source Of Water, Study Says
The water found inside the Moon's mantle came from ancient meteors, not comets, suggesting that lunar water and water on Earth share more in common than previously thought, a new study reports.
To draw the conclusion, researchers examined samples of moon rock brought back during the Apollo missions in the early 1970s.
The Moon is thought to have formed from debris resulting after a giant object smashed into Earth some 4.5 billion years ago, very early in the planet's history. The standing theory presented by the so-called giant-impact hypothesis is that the heat from the collision would have been so intense that any water present on the jettisoned landmass would have evaporated, giving the Moon humbly dry beginnings. But recently, NASA spacecraft and new research on samples from the Apollo missions have shown that the Moon actually has water, both on its surface and beneath, Brown University reports.
The latest findings suggest the Earth was already damp at the time the moon was created, and that the intense heat of the collision failed to vaporize all of the water.
"Some of that water survived the impact, and that's what we see in the moon," said lead study author Alberto Saal, a geologist at Brown University, according to a statement.
To find the origin of the Moon's water, Saal and his colleagues looked at melt inclusions found in samples brought back from the Apollo missions. Melt inclusions are tiny dots of volcanic glass trapped within crystals called olivine. The crystals prevent water escaping during an eruption and enable researchers to get an idea of what the inside of the Moon is like.
Saal and his colleagues looked at the isotopic composition of the hydrogen trapped in the inclusions. "In order to understand the origin of the hydrogen, we needed a fingerprint," Saal said. "What is used as a fingerprint is the isotopic composition."
That fingerprint was hard to take, but after doing some intense analysis the researchers found that the isotropic composition of the moon rock was more akin to material formed closer to the Sun, like meteors, rather than objects that form much further away, like comets.
"The measurements themselves were very difficult," said co-author Erik Hauri, "but the new data provide the best evidence yet that the carbon-bearing chondrites were a common source for the volatiles in the Earth and Moon, and perhaps the entire inner solar system."
According to Saal, as much as 98 percent of the water on Earth also comes from primitive meteorites, suggesting a common source for water on Earth and water on Moon. The easiest way to explain that, Saal says, is that the water was already present on the early Earth and was transferred to the Moon.
The research was co-authored by Erik Hauri of the Carnegie Institution of Washington, James Van Orman of Case Western Reserve University, and Malcolm Rutherford from Brown and published online in Science Express.