Water molecules detected on the surface of an asteroid in space for the first time

The data came from a now-defunct NASA mission and was collected by the Faint Object InfraRed Camera.
A graphic rendering of an asteroid in space, with a close up on where water molecules are on the surface.
Using data from NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), Southwest Research Institute scientists have discovered water molecules on the surface of an asteroid. NASA/Carla Thomas/SwRI

Scientists have detected water molecules on the surface of an asteroid in space for the first time. The findings reveal new details about how water is distributed in the solar system and are detailed in a study published February 12 in The Planetary Science Journal.

[Related: What astronomers learned from a near-Earth asteroid they never saw coming.]

Water molecules have been detected in asteroid samples returned to Earth, but this marks the first time that the molecules have been discovered on the surface of an asteroid in space. The team studied four silicate-rich asteroids using data from the now-retired Stratospheric Observatory for Infrared Astronomy (SOFIA). This plane equipped with a telescope was operated by the German Aerospace Center and NASA. Some observations taken by SOFIA’s Faint Object InfraRed Camera (FORCAST) instrument revealed that asteroids Iris and Massalia have evidence of a specific wavelength of light that indicates that water molecules are present on their surface. The asteroid Iris is giant at 124-miles-diameters and orbits our sun between mars and Jupiter. Massalia is about 84 miles across and is also near the Red Planet.  

“Asteroids are leftovers from the planetary formation process, so their compositions vary depending on where they formed in the solar nebula,” Anicia Arredondo, study co-author and astronomer and asteroid specialist at the Southwest Research Institute, said in a statement. “Of particular interest is the distribution of water on asteroids, because that can shed light on how water was delivered to Earth.”

Dry silicate asteroids are described as anhydrous and they typically form closer to the sun. More icy space rocks like Chariklo are found further away from the sun. Understanding where asteroids are located in the solar system and what they are made from can tell us how the materials in our solar system have been distributed and evolved over time. Since water is necessary for all life on Earth, pinpointing where water could exist can drive where to look for life in our solar system and even beyond.

“We detected a feature that is unambiguously attributed to molecular water on the asteroids Iris and Massalia,” said Arredondo “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.”

The water molecules were detected by SOFIA in one of the moon’s largest craters in its southern hemisphere. Earlier observations of the moon and asteroids have found some form of hydrogen, but could not tell the difference between water and a close chemical relative called hydroxyl. The team found roughly the equivalent of a 12-ounce bottle of water on the crater. The water was chemical bound in minerals and trapped in a cubic meter of soil spread across the lunar surface.

“Based on the band strength of the spectral features, the abundance of water on the asteroid is consistent with that of the sunlit Moon,” said Arredondo. “Similarly, on asteroids, water can also be bound to minerals as well as adsorbed to silicate and trapped or dissolved in silicate impact glass.”

[Related: NASA spacecraft Lucy says hello to ‘Dinky’ asteroid on far-flying mission.]

Parthenope and Melpomene were the two fainter asteroids in the study, and the data did not reveal any definitive conclusions about the presence of water molecules. According to the team, the FORCAST instrument is not sensitive enough to detect the water spectral feature if present here. The team is now getting the help from NASA’s James Webb Space Telescope to use its precise optics and ability to see in infrared signals to investigate other targets in space.

“We have conducted initial measurements for another two asteroids with Webb during cycle two,” said Arredondo. “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.”