Where did Earth’s water come from? Not these meteorites, finds new study

Scientists are one step closer to figuring out where Earth's vast quantities of water come from after disqualifying a class of meteorites drifting around in space since the solar system's birth 4 1/2 billion years ago, according to a new study published in Nature on March 15.

The study may have significant implications for the quest for liquid water and possibly even life on distant planets. It might also aid in understanding the extraordinary circumstances that allowed Earth to become a planet that supports life.

Where did Earth's water come from?

Although it is generally believed that water arrived on Earth from the outer solar system, it is still unknown what kind of objects could have transported it there.

Now, a team has examined seven melted meteorites, also known as achondrites, that struck Earth billions of years ago. These formed after shattering from at least five planetesimals- objects that collided to create the planets in our solar system today. 

They obtained some of their meteorite samples from the inner solar system, where Earth is situated and where the climate is typically believed to be warm and dry. Other rarer pieces came from our planetary system's colder, icier outermost regions.

This experiment was the first to measure the volatiles of these recently impacted meteorites. The group calculated the concentrations of silicon, calcium, iron, magnesium, and other elements using an electron microprobe. They then employed a secondary ion mass spectrometry device to determine how much water was in them.

"We knew that plenty of outer solar system objects were differentiated, but it was sort of implicitly assumed that because they were from the outer solar system, they must also contain a lot of water," said co-author Sune Nielsen in a press release, who is a geologist at the Woods Hole Oceanographic Institution. 

"Our paper shows this is definitely not the case. As soon as meteorites melt, there is no remaining water." 

Achondrite vs. chondrites meteorites

Researchers found that water comprised less than two-millionths of the mass of the achondrite meteorite samples. To put this into perspective, the wettest meteorites, known as carbonaceous chondrites, contain up to around 20 percent of water by weight.

This means that regardless of where planetesimals originated in the solar system and how much water they initially had, their heating and melting result in almost total water loss. The scientists concluded that chondritic, or unmelted, meteorites were most likely responsible for bringing water to Earth.

"Water is considered to be an ingredient for life to be able to flourish, so as we're looking out into the universe and finding all of these exoplanets, we're starting to work out which of those planetary systems could be potential hosts for life," said lead author Professor Megan Newcombe.

"In order to be able to understand these other solar systems, we want to understand our own."

The full study was published in Nature on March 15 and can be found here.