Using data from NASA’s Dawn spacecraft, researchers have found new evidence for the occurrence of ground ice on Vesta, the second largest asteroid of the asteroid main belt.
Large, smooth areas on Vesta correlated with higher concentrations of hydrogen. Image credit: Elizabeth Palmer / Essam Heggy.
Discovered by Heinrich Wilhelm Olbers on March 29, 1807, Vesta is the only main-belt asteroid visible to the unaided eye.
It rotates once in 5.34 hours, orbits the Sun in 3.63 years, and has an ellipsoidal shape with radial dimensions of 286 x 279 x 223 km.
Due to its large size, Vesta is believed to be a differentiated body with a core and a mantle just like our own planet. Collisions between asteroids in the belt enable them to leave their orbits and travel great distances in our Solar System, potentially colliding with other planetary bodies.
Finding ice on these bodies is of major importance to understanding the transport and evolution of water-rich materials in the Solar System.
A research team led by Dr. Essam Heggy of Caltech and the University of Southern California used a special technique called ‘bistatic radar’ on NASA’s Dawn spacecraft to explore the surface texture of Vesta at the scale of a few inches.
“On some orbits, when Dawn was about to travel behind Vesta from Earth’s perspective, its radio communications waves bounced off Vesta’s surface, and mission personnel on the ground at NASA’s Jet Propulsion Laboratory received the signals back on Earth,” Dr. Heggy and co-authors explained.
“This system of radar signaling was like seeing a flame from a lighter in the middle of day from the opposite side of the United States.”
Despite the challenges in measuring such a weak signal from Dawn, the researchers assessed the occurrence of large, smooth areas on Vesta that correlated with the occurrence of higher concentration of hydrogen as measured by Dawn’s gamma ray and neutron detector (GRaND) instrument.
“Our results suggest that unlike the Moon, Vesta’s surface roughness variations cannot be explained by cratering processes only,” the authors said.
“In particular, the occurrence of heightened hydrogen concentrations within large smoother terrains (over hundreds of km2) suggests that potential ground-ice presence may have contributed to the formation of Vesta’s current surface texture.”
“I am excited that we were able to perform such an observation on Vesta,” Dr. Heggy said.
The scientists hope their work will get the public excited not just about water in space, but also about the importance of understanding water evolution in arid areas under changing climatic conditions.
The findings are published in the journal Nature Communications.
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Elizabeth M. Palmer et al. 2017. Orbital bistatic radar observations of asteroid Vesta by the Dawn mission. Nature Communications 8, article number: 409; doi: 10.1038/s41467-017-00434-6
