Earth's water is thought to come from an extraterrestrial source, potentially asteroids.

This theory, known and explored for a few years, was recently validated by the analysis of samples brought back from the asteroid Ryugu by a Japanese space mission.

The study supporting this thesis was published on Monday in the journal

Nature Astronomy


C-type asteroids like Ryugu, "rich in volatile and organic substances", could thus have been "one of the main sources of water on Earth", according to Japanese and foreign researchers involved in the study.

[Press Release]

Asteroid Ryugu is a drifter from the outer Solar System:

Results from the Hayabusa2 Phase-2 Curation Kochi Team

published in Nature Astronomy

— JAXA (Japan Aerospace Exploration Agency) (@JAXA_en) August 16, 2022

Access to this content has been blocked to respect your choice of consent

By clicking on "


", you accept the deposit of cookies by external services and will thus have access to the content of our partners


And to better remunerate 20 Minutes, do not hesitate to accept all cookies, even for one day only, via our "I accept for today" button in the banner below.

More information on the Cookie Management Policy page.

Extremely rare samples full of promise

"The contribution to the Earth of volatile substances, that is to say organic matter and water, is still the subject of an important debate", recalls the report.

But the organic substances identified on Ryugu "probably represent an important source of volatile substances", in addition to other potential sources such as solar winds, according to the researchers.

The particles brought back from Ryugu are "without a doubt" among the "least contaminated" materials from our solar system available for laboratory study.

According to the researchers, research on these samples "will certainly expand our understanding of early processes in the solar system".

Many discoveries to come

Discovered in 1999, Ryugu (“Dragon Palace” in Japanese) is located more than 300 million kilometers from Earth and is less than 900 m in diameter.

Scientists believe that some of the material from this asteroid was created about five million years after the birth of our solar system and was not heated above 100°C.

In 2019, the Hayabusa-2 probe managed to collect 5.4 g of rock and black dust from Ryugu.

The capsule containing these samples returned to Earth at the end of 2020, with the promise of delivering new clues to the origin of life on Earth.

In June, a study had already revealed the presence in these samples of amino acids, molecules at the base of life, since they are capable of forming proteins.


The star was actually a slice of chorizo, a scientist traps Internet users on Twitter


A 50,000-year-old meteorite contained a never-before-seen form of diamond

  • Science

  • Asteroid

  • Water

  • Earth

  • Space

  • Japan