spaceSpace and Physics

There Might Be Another Way That Earth Got Its Water Billions Of Years Ago


Jonathan O'Callaghan

Senior Staff Writer

Water, water everywhere. NASA

Scientists have proposed a possible new origin for Earth’s water, saying it may have been delivered by the early environment around the Sun, as well as from asteroids or comets.

The origin of our water has long been debated. Most theories seem to point to water-rich comets or asteroids delivering the water at some point after the planet had formed more than 4 billion years ago.


But in a paper published in Geophysical Research: Planets, a team led by Jun Wu from Arizona State University investigated another method. They suggest the solar nebula that our planet was born in could have supplied our planet with hydrogen necessary to form water.

“For every 100 molecules of Earth’s water, there are one or two coming from solar nebula,” Wu said in a statement.

The idea that water was delivered to our planet after it formed has been questioned of late, notably because comets like 67P/Churyumov-Gerasimenko were found to have the wrong type of water. Namely, they have a different ratio of hydrogen to an isotope called deuterium.

So at least some of our water must have come from somewhere else. And this latest research points to our Sun’s environment. The team created a model that showed that 4.5 billion years ago at the birth of the Solar System, large asteroids began forming into the planets like Earth.


One of these, a magma-covered embryo, would become our planet – but in the process, it scooped up gas from the solar nebula including nebula hydrogen. This would have been pulled towards the core of our planet.

"The end result… is that Earth likely formed with seven or eight global oceans' worth of hydrogen,” Steven Desch from Arizona State University, a co-author on the study, said in a separate statement.

“The majority of this indeed came from asteroidal sources. But a few tenths of an ocean's worth of hydrogen came from the solar nebula gas." 

Aside from being interesting for our own planet’s formation, the research is important for other worlds too. It suggests exoplanets, those beyond our Solar System, did not need to rely on asteroid impacts to get water – it could have been delivered by the nebula of their own stars.


“This model suggests that the inevitable formation of water would likely occur on any sufficiently large rocky exoplanets in extrasolar systems,” said Wu. “I think this is very exciting.”


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