Earth’s Water May Be Older Than The Sun, ALMA Finds

At Fact Fun, we often look back at Earth’s origins, but this time scientists looked even further — and what they found rewrites our cosmic story. According to a series of recent studies, the water flowing in our oceans might be billions of years older than the Sun itself.

A Telescope Peering Back in Time

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers have spent several years studying a young star called V883 Orionis, located in the Orion constellation roughly 1,300 to 1,350 light-years from Earth. Its surrounding disk of gas and dust is where planets are actively forming — a cosmic snapshot of how our own Solar System likely looked 4.6 billion years ago.

In 2023, a team led by astronomer John Tobin of the National Radio Astronomy Observatory (NRAO) made the first direct detection of water vapor in this planet-forming disk, along with a standard form of heavy water. The ratio of heavy water to normal water closely matched what’s found in comets within our own Solar System, hinting that Earth’s oceans and space-born ice might share the same ancient origin. That research was published in the journal Nature.

Older Than Our Star

Then, in October 2025, a follow-up study pushed the story even further. A team led by astronomer M. Leemker, with Tobin now serving as a co-author, made the first-ever detection of doubly deuterated water (D₂O) — an even heavier variant of water — in that same disk around V883 Orionis. This particular molecule is considered a much stronger chemical fingerprint of truly ancient, unprocessed ice, the kind that would have existed in the cold interstellar cloud long before any star ignited.

“Until now, we weren’t sure if most of the water in comets and planets formed fresh in young disks like V883 Ori, or if it’s ‘pristine,’ originating from ancient interstellar clouds,” said John Tobin. “This finding is the first direct evidence of water’s interstellar journey from clouds to the materials that form planetary systems — unchanged and intact.”

The 2025 findings, published in the journal Nature Astronomy, suggest that much of the water present in our Solar System — including the water on Earth — likely didn’t originate here at all. Instead, it may have been inherited almost unchanged from the cold molecular cloud that eventually collapsed to form our star and planets.

How Heavy Water Tells Ancient Stories

Because deuterium enrichment only builds up efficiently in extremely cold conditions, typically below about -240°C (30 Kelvin), the presence of heavy water acts almost like a chemical fossil, marking where and roughly when a batch of water molecules first formed. By tracing these ratios in V883 Orionis’s disk, astronomers can follow water’s journey from interstellar space all the way to newborn worlds, showing that many of the same molecules likely floated through space long before our Sun, or Earth, ever existed. If distant, otherworldly discoveries fascinate you, you might also enjoy exploring the mystery of the universe’s rotation and the Hubble tension or how NASA detected a 7,000-kilometer gravity anomaly over the Atlantic — two other stories that push our understanding of space even further.