Water may have been brought to our planet by meteorites during the first two million years of after the birth of the solar system, a study has found. Since elements such as water and carbon are essential ingredients to life on Earth, researchers are keen to know when they arrived on our planet. “We’re looking at as many meteorite parent bodies as possible right now to figure out where they were in the early solar system and how much water they had,” said Adam Sarafian, from the Massachusetts Institute of Technology (MIT) in the US. Angrite meteorites formed in the inner solar system extremely early, roughly 4.56 billion years ago. At that point, the Earth was likely still just 20 per cent of its current size, while Mars, which formed more quickly, was probably close to its current size. Scientists are not sure how quickly Mercury and Venus were formed.
During this time, the inner solar system was a hot and dry place. Protoplanets and asteroids had molten surfaces and, when in magma, even an element such as carbon, which has a boiling point of 4,800 degrees Celsius is considered to be an volatile. It has therefore been unclear when delicate, low-boiling-point elements such as water came aboard, particularly as the hydrogen required to make water molecules would have been boiled away by the high temperatures.
Researchers measured a common mineral in basaltic meteorites, called olivine, for the volatile elements hydrogen, carbon, fluorine and chlorine. “Once we know the melt composition, we can then calculate what a planetary body’s water content was,” Sarafian said. The team discovered that the parent asteroid of angrites likely had about 20 per cent of the Earth’s current water content.
While the percentage is low by modern terms, this amount of water in the early solar system indicates that water was fairly abundant 4.56 billion years ago, even when the inner solar system was still hot. Different sources of water in the solar system are commonly compared to Earth’s water by measuring the ratio of the hydrogen isotope deuterium to hydrogen (D to H).
Previous research showed that the angrite parent body’s water matches the Earth’s water composition perfectly. This suggests that both the water found in angrites and early Earth’s water came from the same source. “It’s a fairly simple assumption to say that Earth’s water at least started accreting to Earth extremely early, before the planet was even fully formed,” said Sarafian. “This means that when the planet cooled enough so that liquid water could be stable at the surface, there was already water here,” he said.
By the time Earth was fully-formed 4.54 billion years ago, Mars already had a 20 million year head start as a stable mass with water and other volatiles on its surface, such as carbon, fluorine, and chlorine, said Sarafian.