For the first time, astronomers have confirmed that an asteroid contains frozen water on its surface.
Analysis of asteroid 24 Themis shows evidence of water ice along with organic compounds widespread across the surface. The scientists say these new findings support the theory that asteroids brought both water and organic compounds to the early Earth, helping lay the foundation for life on the planet.
Humberto Campins of the University of Central Florida in Orlando and colleagues recorded spectra of 24 Themis over a seven-hour period, and were able to study 84 percent of the rotational period of the spinning rock, Rob Cowen reported in Science News. Using NASA’s Infrared Telescope Facility on Hawaii’s Mauna Kea, the spectra revealed the consistent presence of frozen water as different parts of the asteroid’s surface came into view.
Analyses of the sunlight reflected off the asteroid also show that organic compounds are widespread on the surface, he added, including polycyclic aromatic hydrocarbons, CH2 and CH3.
The new finding corroborates earlier observations of the same asteroid by astronomers Andrew S. Rivkin and Joshua Emery who also used the Infrared Telescope Facility. Over several years, Rivkin and Emery had found evidence of frozen water in single spots on 24 Themis but had not studied the asteroid as it made one entire rotation. Together, the two teams’ findings reveal that the asteroid’s entire surface is coated with frozen water, Campins says.
The 160-kilometer wide asteroid averages a distance from the sun of about 3.2 times that of Earth’s. At that range, frozen water on the surface would readily vaporize, Campins said. That means the ice must be continually replenished, possibly by a reservoir of frozen water within the rock.
One possibility is that ice lies buried several meters below the surface of 24 Themis, and when hit by space debris, the ice makes its way to the surface. If this is the case, it could confirm that some asteroids resemble comets, becoming active suddenly and venting material into space when pockets of ice vaporize, Campins said.
Another option is that an action similar to the recent findings of water on the Moon, where solar wind interacts with a rocky body without an atmosphere to create H2O and OH molecules. Without an atmosphere, the body is exposed to solar wind, which includes hydrogen ions. The hydrogen is able to interact with oxygen in surface of the asteroid to create water molecules.
Campins shared his findings at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences.
Nancy Atkinson
