Astronomers have discovered that in the early days of the Solar System’s formation, the asteroid Ryugu—the diamond-shaped target of the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 mission—had a small ocean inside it.

Before it became today’s asteroid, high-precision isotopic analysis shows that it was part of a larger, older parent asteroid before it was destroyed in a collision.

But even more surprising is the fact that in this small ocean some dried silicates from the original parent asteroid managed to survive intact.

A new paper by one of the Hayabusa team, published in Nature Astronomyanalyzes the composition of Ryugu’s parent and asteroids in the early Solar System.

In December 2020, Hayabusa2 returned just over five grams of asteroid Ryugu after a six-year mission.

What have astronomers discovered in this ocean?

Since the samples represent a relatively limited number of tiny grains, each one has been labeled with its own name and number. In this case, the team’s analysis was based on just one of these particles, C0009.

Thus, isotope cosmochemist Ming-Chang Liu of UCLA explains that C0009 was particularly interesting because “it was distinguished by having a small amount of anhydrous silicates”—that is, it contains oxygen-enriched minerals unaffected by water in the middle of a sample heavily altered by H2O, he explained to Inverse.

Ryugu’s composition was significantly altered by the liquid water within him.

Despite having formed in the cold depths of the outer Solar System, water and carbon dioxide ice accumulated together in the protolith that formed Ryugu’s parent, along with short-lived radioactive isotopes.

The composition of asteroid Ryugu as modified by the liquid water inside it

As these radioactive rocks heated the ice around them, “they would have begun to float inside the parent body” — and over time, transform the silicates and pyroxene that made up Ryugu’s predecessor into water-bearing phyllosilicates, he writes Inver.

Thus, the remaining anhydrous silicates give the team a hint of what other material in the early Solar System might have looked like before it collapsed into Ryugu’s small ocean. And the materials look like the first materials formed in the Sun’s photosphere.

Oxygen isotopes in the team’s sample show that the asteroid contains amoeboid olivine and magnesium-rich chrondrules that were incorporated directly from the solar nebula.

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