Vital information transmitted by Dawn mission spacecraft
By Ann McCreary
A scientist at the Bear Fight Institute near Winthrop has described the first and only confirmed detection of water-rich material at the surface of Ceres, a dwarf planet in the asteroid belt between Mars and Jupiter.
Jean-Philippe Combe authored a research article published Friday (Sept. 2) in the journal Science, detailing the discovery of water ice on Ceres.
Information leading to Combe’s discovery was transmitted by NASA’s Dawn spacecraft, which is orbiting Ceres.
The detection of water ice on Ceres is inherently intriguing, Combe said in an interview last week.
“Anything that involves water is very interesting and exciting. Water is an essential substance in the general evolution of any planet, and also for the creation of life, the type of life that we know anyway,” Combe said.
“Water in our solar system is potentially related to creation of life. You have to start with detection of H20 to go further,” he said.
That’s not to imply that Ceres provides any indication of supporting life, Combe said. Of interest, though, is the presence of the water ice on the surface of Ceres, Combe said.
Planetary scientists have long suspected that the interior of Ceres is composed of large amounts of water or ice, Combe said.
“We knew that from the measurements of density of Ceres there has to be some ice in the bulk of Ceres. It is not dense enough to be made entirely of rocks. The obvious component was ice,” he said.
Finding the water ice on the surface was surprising, Combe said.
The water ice was detected using a Visible and InfraRed Mapping Spectrometer (VIR) carried aboard the Dawn spacecraft, which began orbiting Ceres in March 2015.
The VIR measures the sunlight scattered on the surface of Ceres in a range of wavelengths from the near ultraviolet to the near infrared. Data obtained through VIR reveals mineral and molecular composition, and in this case revealed the presence of water.
The water ice was observed in a 10-kilometer-wide crater named Oxo. Combe said the crater’s location on Ceres protects much of the surface area from solar illumination, providing favorable conditions for stability of water ice.
The Oxo crater “appears to be geologically very young — 1 million to 10 million years old,” Combe said. It has sharp rims and a portion of the rim has collapsed toward the center “like a landslide,” he said.
“It casts shadows on the floor of the crater, mostly the floor is in complete shadow. Only around the summer solstice on Ceres is the floor illuminated. Fortunately, Dawn observed it at this time,” Combe said.
The water ice was observed close to the shadow cast by the scarp — a steep slope caused by the landslide, he said.
“The question is, what is the process that made the water present here?” Combe said.
There could be different explanations, he said. The impact that created Oxo might have exposed ice underneath the surface. “Since Oxo is recent, that’s plausible,” Combe said.
The landslide may be active today, and flowing material could have exposed ice in the process. Or there may be some process “that replaces the water at the surface. It may come from underneath,” Combe said.
“If water goes from subsurface or deeper inside to the surface, there may be some process that carries this water. It is possible … that there is a small layer of liquid water inside Ceres. If there is liquid water, that is even more interesting,” he said.
Combe’s article was one of six published in the recent issue of Science about Ceres based on observations made by the Dawn spacecraft. His article was co-authored by Tom McCord, founder and director of Bear Fight Institute.
Dawn was launched in 2007 to study the two largest objects in the asteroid belt between Mars and Jupiter — an asteroid called Vesta and Ceres.
Dawn orbited Vesta from July 2011 through September 2012, then flew on to Ceres. Dawn traveled more than 3 million miles since leaving Earth, and is the first spacecraft to orbit two different planetary bodies beyond the Moon-Earth system.
Combe has been working at Bear Fight Institute, located in the upper Rendezvous area, for 10 years.
Born in France, he studied applied physics and specialized in remote sensing. Combe was working on his doctoral thesis, which involved mapping Mars, and his adviser in France was a collaborator with McCord, who was looking for another scientist for Bear Fight. Combe took the job.