This project follows from the recent discovery, by three independent spacecraft, of evidence for either water-bearing or OH-bearing minerals on the surface of Earth's Moon. The PI and co-PI will perform groundbased near-infrared imaging and spectroscopic observations of a wide range of Solar System objects in order to study the spectral absorption features in the vicinity of 3 microns, generally interpreted to be indicators of water or OH. Their targets will include: the Moon, Mercury, near-Earth and main-belt asteroids, and other planetary satellites. With these observations, coupled with data already in hand and archival datasets, they will test the hypothesis that lunar water arises from surface interactions with the Solar wind by looking for a spectral dependence on surface temperature, illumination (phase) angle, and immersion of the body in a planetary magnetic field. The work is relevant both to geophysics and solar physics in its potential to constrain both solar wind properties and surface histories; an understanding of the origin of lunar water is also key to plans for human exploration of the Moon.
We were awarded support from the NSF to study water on near-Earth asteroid (NEA) surfaces. We know water (which is made of two hydrogen atoms and one oxygen atom) and/or hydroxyl (which is a piece of a water molecule and consists of one oxygen atom and one hydrogen atom) are present in asteroids because we find them in some meteorites, and meteorites come from asteroid surfaces. There has been speculation that hydroxyl is constantly formed on surfaces like the Moon, where hydrogen from the Sun interacts with oxygen in rocks. Knowing whether this also happens on asteroids, and if so how much hydroxyl is made, is important to understanding scientific questions like how the solar system and planets formed and where Earth got its water. It is also important for companies that are hoping to mine asteroids in coming decades and will be useful knowledge in case we need to move or deflect an asteroid that is inbound for an impact. We focused our efforts on three near-Earth asteroids. We observed them using telescopes on the Earth, studying the infrared light they reflect from the Sun. The asteroid 1996 FG3 was one of our targets, and we already suspected it should be like those meteorites that have water. We confirmed that hydroxyl was present, making it only the second NEA on which hydroxyl has been found. This is important because some scientists suspected asteroid surfaces could get hot enough to destroy hydroxyl. The second target was 1036 Ganymed. This target is associated with a group of meteorites that do not have any water or hydroxyl. However, we did find some evidence that a small amount is present on its surface. This is strong evidence that some process like what we mentioned above is occurring, and hydroxyl is being created or brought to its surface by impacts with bodies like 1996 FG3. We observed Ganymed over several years to see it from different angles and directions, and the details of how its reflected light changed with viewing direction give us details of where on its surface the hydroxyl is present. We are continuing to study that aspect. Finally, we observed 433 Eros, which was the target of the NEAR Shoemaker mission. That mission gave us close-up views of the surface, but was unable to measure water. As with Ganymed, we detected a small amount of water or hydroxyl on its surface. However, while the meteorite type most like Eros usually is not found to have water, it is not unknown. So we are not certain whether Eros' water was present from the beginning like 1996 FG3's or if it was brought or created later like Ganymed's.
