Infrared satellite imagery of near-Earth objects have picked up the presence of mineral crystals that contain liquid water. Japanese researchers remarked that this was the first time hydrated minerals have been found inside asteroids. Further investigation of these imprisoned water samples can tell us about how our planet got its water in the first place.

Earth is the sole planet in the Solar System with indisputable proof of liquid water on its surface. But no one knows exactly where all of this water came from. Nor do they know where the water in some of the other, currently dry planets like Mars went to.

One of the most popular theories involves asteroids. When water came into contact with the waterless rock crystals inside an asteroid, they could trigger a chemical reaction called aqueous alteration. This process trapped water inside the crystals, creating hydrated minerals.

Hydrated minerals will stay stable at temperatures that will cause water ice to vaporize into gas. The odd water-containing crystals are a good way to figure out if an asteroid contained water. (Related: NASA’s OSIRIS-REX mission will examine samples from an asteroid, seeking clues to the origin of life.)

Asteroids near Earth have water in the form of hydrated minerals

Kobe University researchers led their counterparts from JAXA and the University of Tokyo in examining spectroscopic images taken by the Japanese satellite AKARI. The infrared camera aboard the spacecraft could identify the distinct spectral features of a substance based on how it absorbed or reflected an infrared wavelength.

Hydrated minerals absorb infrared light with wavelengths of 2.7 micrometers. This was within the detection range of AKARI’s infrared camera, which covered wavelengths from two to five micrometers. Other space telescopes either lacked sufficiently sensitive sensors or didn’t cover this wavelength range.

The researchers used AKARI to scan 66 asteroids near Earth. The near-infrared spectra of these space rocks were analyzed in order to determine the amount of hydrated minerals locked within the target.

In their report, they found signs of hydrated crystals in 17 carbonaceous (C-type) asteroids. In addition to the crystals, they also spotted the infrared characteristics of water ice and considerable amounts of ammonia.

The study was the first to confirm the presence of hydrated minerals — and by extension, water — on the asteroids. Their findings support the leading theory that C-type asteroids contained both organic material and water.

Hydrated asteroids are slowly losing water, while some “dry” asteroids are actually “wet” ones

Furthermore, the researchers found evidence that something is heating the hydrated minerals, which causes the crystals to slowly but surely evaporate their water content. They do not know what is causing the heat; it could be micrometeorite hits, the decay of radioactive isotopes in the rocks, or the ionized gas borne upon solar wind.

A good number of the C-type asteroids in the study demonstrate this behavior. Researchers guessed that these asteroids were born from a mishmash of rocks and water ice. Once the asteroid itself was formed, aqueous alteration took place within it and created the hydrated minerals.

Scans of the other common type of asteroid, the siliceous or S-type, provided a small surprise. These nickel-iron space rocks were believed to be “dry,” but it turned out that a few of them appear to also contain small amounts of hydrated minerals.

For these exceptions, the researches believe that the S-type asteroids got their supply of water during collisions with hydrated C-type rocks. Collisions between asteroids are rare but confirmed.

Such events would have been more common during the early years of the Solar system. Those that hit Earth might have added their hydrated minerals to the planet’s stock of water.

Sources include:

AlphaGalileo.org

ARXIV.org