Q&A: Water Found on Asteroid

By Dan Verderosa, December 13, 2018
IC professor and OSIRIS-REx mission asteroid scientist Beth Ellen Clark discusses the discovery of water on Bennu.

On Dec. 10, scientists working on NASA’s OSIRIS-REx mission announced that they had discovered evidence of water on the asteroid Bennu. The important finding suggests that water may have been common in the early days of the solar system.

Physics professor Beth Ellen Clark is the mission asteroid scientist for OSIRIS-REx, responsible for managing several of the experiments conducted during the years-long mission to study and return a sample from Bennu, including the analysis that found evidence of water. In an interview with IC News, she discussed the importance of the mission’s water discovery and what else scientists have learned since the OSIRIS-REx spacecraft reached the asteroid.

IC NEWS: What is the significance of the discovery of evidence that water once existed on Bennu?

CLARK: There are several reasons why this is important. First, scientists theorize that the early Earth was too energetic a place — picture volcanos and churning lava — to support a hydrosphere. We think any early hydrosphere would have been boiled off the planet. But that means that we need an external source of water to explain the presence of our current hydrosphere. The delivery of water-rich meteorites and cometary materials later on during the evolution of the Earth could explain our current oceans. So, having some samples of this material will help us to understand this interesting phase of planet building in our solar system, and possibly in other solar systems. This will help us to understand the origins of Earth, and of life on Earth.

Prior to mission launch in 2016, professor Beth Ellen Clark discusses the OSIRIS-REx mission and how Ithaca College students have been involved.

Second, there is a class of meteorites that are extremely rare in our Earthly meteorite collections — CI chondrites — which are rich in carbon and water held in minerals. Our first spectroscopy data of Bennu could be telling us that Bennu is composed of, or is similar to, this rare type of meteorite! Bringing back samples of this rare type of solar system material could make a significant difference in our access to, and our understanding of, such material. 

Third, the asteroid mining community has set a commercial price point for mining water on asteroids, and if Bennu’s water is held in clays and other water-rich minerals on the surface, that would make asteroids like Bennu attractive for mining water. That water would be used to more cheaply produce rocket fuel in space. Apparently, it would be easier to mine the water from an asteroid and deliver it to Earth orbit to be made into fuel than it would be to launch water from the surface of the Earth to the same position. It is amazing and almost sci-fi to be living in an age when asteroid mining is being seriously considered!

IC NEWS: How did the scientists working on OSIRIS-REx find evidence of water?

A woman holding a model asteroid

Professor Beth Ellen Clark holds a model of the asteroid Bennu. (Photo by Adam Baker/Ithaca College)

CLARK: Our OSIRIS-REx Visible Infrared Spectrometer detected an absorption at 2.7 microns in the reflectance spectrum of Bennu, which is the signature of hydroxyl ions — pieces of water molecules — in clay-like, hydrated minerals called phyllosilicates.

IC NEWS: Photos of Bennu show the asteroid’s surface littered with rocks and boulders. What does that tell you about its origins?

CLARK: My colleague Patrick Michel from the Observatoire de la Côte d'Azur theorizes that Bennu is round because it was part of a larger asteroid that was catastrophically disrupted and then re-accumulated slowly in very low gravity conditions. This would explain why it is round and why giant boulders are sitting around on the surface, showing no association with craters or crater remnants.  

IC NEWS: As mission asteroid scientist, you are in charge of managing OSIRIS-REx’s thermal analysis, spectral analysis and visual color imaging analysis. What will those analyses tell us about Bennu?

CLARK: These analyses will determine the composition of Bennu, the thermophysical properties of Bennu, and what sorts of alteration to Bennu’s surface properties may be occurring in the space environment. The thermophysical investigation is particularly exciting because we’re hoping to learn more about how Bennu’s afternoon re-emission of the heat from the sun changes its orbit over time. If we can understand these thermal forces a little better, then we can predict the future orbits of these asteroids, and hopefully be able to predict in advance if or when an asteroid is headed our way, on course to impact the Earth.

This interview has been edited for length and clarity.