Water molecules discovered on asteroid's surface for the first time

Using data from NASA's now-retired SOFIA telescope, scientists at the Southwest Research Institute have discovered, for the first time, water molecules on the surface of an asteroid.

The SwRI team used the Faint Object InfraRed CAmera for the SOFIA Telescope (FORCAST) to study four silicate-rich asteroids, namely Iris, Parthenope, Melpomene and Massalia. By isolating mid-infrared spectral signatures, they successfully identified molecular water on two of these asteroids.

Anhydrous or dry, silicate asteroids form close to the Sun while icy materials coalesce farther out. Understanding the location and composition of these asteroids provides insights into how materials in the solar nebula were distributed and have evolved since formation. Understanding water distribution is crucial for identifying potential life-harbouring planets both within our solar system and beyond because water is essential for life as we know it here on Earth.

Previously, SOFIA detected water molecules in one of the largest craters in the lunar southern hemisphere. While past observations of both the Moon and asteroids had detected some form of hydrogen, distinguishing between water and hydroxyl had remained a challenge. Scientists detected roughly equivalent to a 12-ounce bottle of water trapped in a cubic meter of soil spread across the lunar surface, chemically bound in minerals.

The team's attempt to draw conclusive evidence of water on two fainter asteroids, Parthenope and Melpomene, was hindered by noisy data. The FORCAST instrument is apparently not sensitive enough to detect the water spectral feature if present.

The SwRI researchers now plan to leverage the precise optics and superior signal-to-noise ratio of NASA's James Webb Space Telescope to investigate more targets.

"We detected a feature that is unambiguously attributed to molecular water on the asteroids Iris and Massalia. We based our research on the success of the team that found molecular water on the sunlit surface of the Moon. We thought we could use SOFIA to find this spectral signature on other bodies," said SwRI's Dr. Anicia Arredondo, lead author of a Planetary Science Journal paper about the discovery.

"We have conducted initial measurements for another two asteroids with Webb during cycle two. We have another proposal in for the next cycle to look at another 30 targets. These studies will increase our understanding of the distribution of water in the solar system," Arredondo added.

SOFIA, a Boeing 747SP jetliner modified to carry a reflecting telescope, achieved full operational capability in 2014 and ended operations in September 2022. It was a joint project of NASA and the German Space Agency at DLR.