Water found on asteroid could shed light on origins of life on Earth

Environment ‘similar to the Earth’s oceans’ likely existed in Ryugu’s interior, scientists say

Scientists have found liquid water trapped in crystals within rock samples returned from the asteroid Ryugu about 300 million km (186 million miles) from Earth.

Samples of the asteroid were found to contain a range of minerals, including calcium and aluminium-rich particles, magnetic minerals like magnetite, as well as carbonated water containing salts and organic matter.

The samples were returned to Earth for analysis by the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 mission in 2020.

The findings, published in the journal Science on Friday, offer more evidence supporting the theory that life – or life-precursor molecules – on Earth might have originated from space.

“Liquid water trapped in crystals in the sample was found. The water was held in micron-sized vacancies,” JAXA said in a statement.

In the study, scientists analysed 17 Ryugu samples measuring about 1-8mm and found an iron sulphide pyrrhotite crystal containing carbonated water.

Researchers suggested that the parent space rock from which the Ryugu asteroid descended was born in the darkness of a stellar gas cloud located far from the reaches of the Sun’s light.

In this parent body, they said there would be variations in the ratio of water to rock between the surface and the interior, with rocks deeper underground containing more water.

Simulations conducted by the scientists suggested Ryugu’s parent body accumulated about 2 million years after the formation of the Solar System, and then heated up to about 50C over the next 3 million years, resulting in chemical reactions between water and rock.

The asteroid’s samples were found to contain some material near the surface of the parent body before its impact destruction and some from the interior of the parent space rock.

Scientists likened the hardness of the samples to that of volcanic igneous rocks on Earth, making them soft and allowing them to be easily cut with a blade.

Researchers found a diverse set of minerals in these rock fragments, whose differences, they said, can be explained by the different conditions for chemical reactions with water.

Scientists said the hydrous minerals, including silicates and carbonate compounds discovered in the asteroid sample, likely formed when raw materials in the parent body reacted with water and carbon dioxide in the interior of the giant space rock.

Based on the state and stability of some of these minerals, researchers said the water temperature in some parts of the parent rock may have been about 25C.

Other studies have also suggested that the magnetite iron minerals in the Ryugu samples formed “surprisingly low” temperatures of under 40C.

The new analysis also revealed “coral-like crystals” grew from Ryugu’s liquid water.

Based on these findings, researchers said an environment “similar to the Earth’s oceans” existed in Ryugu’s interior, adding that such water-bearing asteroids are more widely distributed in the Solar System than water-free objects.