Water molecules on asteroids thought to be 'completely dry'

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Water molecules have been discovered on the surface of asteroids for the first time, proving that these remnants from the formation of our solar system are not just dry space rocks.

Astronomers believe the impact of asteroids colliding with our planet may have helped deliver water and other elements to early Earth, so finding evidence of water on asteroids could support that theory, according to a new study.

The data were collected from an instrument on the airborne telescope at the now-retired Stratospheric Observatory for Infrared Astronomy. The infrared telescope, called SOFIA, flew on a Boeing 747SP modified to fly through the stratosphere above 99% of Earth's atmosphere, blocking infrared light.

The SOFIA telescope's Faint Object Infrared Camera, or FORCAST instrument, allowed astronomers to detect water molecules on Iris and Masalia, two asteroids in the main asteroid belt between the orbits of Mars and Jupiter. Both are more than 223.1 million miles from the sun.

The results were published on Monday Planetary Science Journal.

Astronomers were inspired to use SOFIA to study asteroids beyond the telescope Evidence of water has been spotted on the moonsaid lead study author Dr. Anicia Arredondo, a research scientist at the Southwest Research Institute in San Antonio.

Evidence of wetting on the two asteroids was previously found by study co-author Dr. Maggie McAdam, a research scientist at NASA Ames Research Center in Mountain View, California, while using a different telescope. Arredondo said researchers weren't sure whether water or another molecular compound like hydroxyl was causing the wetting.

“Our new observations with SOFIA have conclusively indicated that what they saw was indeed water,” Arredondo said. “But these objects are part of the S class of asteroids, which means they are composed mostly of silicates, and until Dr. McAdam’s results, it was assumed that they were completely dry.”

Arredondo said the amount of water the team discovered was roughly equivalent to the amount of water in a 12-ounce water bottle trapped inside a cubic meter of soil, which is similar to what SOFIA discovered on the moon. The telescope captured the signature of water molecules in one of the largest craters in the Moon's southern hemisphere in 2020.

Like water on the moon, “on asteroids, water can also bind to minerals as well as be adsorbed by silicates and trapped or dissolved in silicate glass,” Arredondo said.

Asteroids are remnants of when the planets formed in our solar system. Studying their compositions can tell astronomers where asteroids originated in our cosmic neighborhood.

“When the solar system was forming, different materials formed depending on its distance from the sun because material (further) from the sun cooled faster (than) “The materials are closer to the sun,” Arredondo said via email. “This is why the inner planets like Earth and Mars are made of rock and the outer planets like Neptune and Uranus are made of ice and gas.”

The discovery of water in Eris and Massalia could help astronomers trace the history of these particular asteroids, suggesting that their formation occurred far enough from the sun to avoid boiling their water with heat.

Researchers tried to look for water on two other asteroids using SOFIA, but the detection was very faint. And now the team uses James Webb Space Telescope To focus on different asteroids and search for water signatures.

While Webb's observations continue, Arredondo said the initial results have encouraged the team to ask for time to observe 30 more asteroids with the powerful infrared telescope.

“The JWST telescope is much larger than the SOFIA telescope, so it can collect data of higher quality, and it can collect data on more asteroids in a shorter period of time,” Arredondo said. “I hope to be able to observe many different asteroids using the James Webb Space Telescope to look for the signature of water, and I hope to be able to inventory the water in the asteroid belt.”

Webb could help astronomers better understand the distribution of water across the solar system, as well as the composition of different types of asteroids.

“We really didn't expect to find water on these silicate-rich asteroids,” Arredondo said. “Mostly when we talk about water on asteroids, we're talking about more carbon-rich asteroids, e.g Asteroid Bennu Which NASA's OSIRIS-REx mission went to. Now I want to look for trends between moisturizing amount and formulation. I want to know if carbon-rich asteroids contain much more water than silicate-rich asteroids, or if they contain similar amounts.