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Evidence of water discovered in 17 asteroids

Image credit: Pixabay

Using the infrared satellite Akari, a Japanese research team has detected the existence of water in a number of asteroids, bringing scientists a step closer to discovering the origin of water on Earth.

Researchers from the Japan Aerospace Exploration Agency (Jaxa) and the University of Tokyo found that water is retained in asteroids as hydrated minerals, which were produced by chemical reactions of water and anhydrous rocks that occurred inside the asteroid.

This discovery will contribute to our understanding of the distribution of water in our solar system, the evolution of asteroids, as well as the origin of water on Earth, the researchers said.

According to the study - presented in the Publications of the Astronomical Society of Japan - hydrated minerals are stable even above the sublimation temperature of water ice. By looking for hydrated minerals, scientists can investigate whether asteroids contain water.

The study states that Earth is an aqua-planet and the only planet in our solar system where the presence of water on the surface has been confirmed. However, it is unclear how water on Earth originated, with recent studies having shown that other celestial bodies have, or used to have, a form of water.

“Asteroids are considered to be one of the candidates that brought water to Earth. Note that the liquid water is not flowing on the surface of asteroids, but water is retained in asteroids as hydrated minerals, which were produced by chemical reactions of water and anhydrous rocks that occurred inside the asteroids - that is, aqueous alteration,” the research highlights.

At the early stage of the solar system formation, several small bodies including asteroids were larger than they are now and collisions must have been more frequent. For this reason, it is expected that at least some water was brought to Earth by such collisions.

An artist’s illustration of the near-infrared spectroscopic observation with the infrared satellite AKARI.

An artist’s illustration of the near-infrared spectroscopic observation with the infrared satellite AKARI. By using a space-borne telescope, the team was able to successfully detect the presence of water.

Image credit: Kobe University

The spectra of the observed asteroids show common patterns, with the size and distance of the asteroid is important in making differences of the spectra. According to the researchers, to fully understand the patterns they have observed, further observations of more asteroids and a comparison of the measurement of meteorites collected on Earth are required.

Professor Fumihiko Usui, project assistant from Kobe University said: “By solving this puzzle, we can make a significant step towards identifying the source of Earth’s water and unveiling the secret of how life began on Earth.”

Using Akari, the researchers used infrared wavelengths which contain characteristic spectral features of various substances, such as molecules, ice, and minerals, all of which cannot be observed at visible wavelengths.

“Hydrated minerals exhibit diagnostic absorption features at around 2.7 micrometres. The absorption of water vapor and carbon dioxide in the terrestrial atmosphere prevents us from observing this wavelength with ground-based telescopes. It is necessary to make observations from outside of the atmosphere, that is, in space,” the study said.

The Japanese infrared satellite, which was launched in February 2006, was equipped with the Infrared Camera (IRC) that allowed the team to obtain spectra at near-infrared wavelengths from 2 to 5 micrometres.

Using this function, the spectroscopic observations of 66 asteroids were carried out and their near-infrared spectra were obtained, providing the first opportunity to study the features of hydrated minerals in asteroids at around the wavelength of 2.7 micrometres.

In September, four stars were identified as the possible birth place of an interstellar asteroid, known as Oumuamua, which invaded our Solar System last year.

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