NASA’s Dawn spacecraft is about to make a historic arrival at the dwarf planet Ceres on March 6, and it has already sent back some images of the asteroid as it gets closer. The spacecraft will orbit the icy body and provide important insights into the formation of the planet and the history of the solar system — as well as investigate the possibility of life existing there at one point. Science Recorder interviewed Dr. Marc Rayman, the chief engineer and mission director for the Dawn mission at NASA’s Jet Propulsion Laboratory, about what the mission hopes to accomplish and what secrets Ceres may hold.
What do you hope to learn when you enter orbit around Ceres?
Ceres is the only world of ice and rock that we are going to orbit. Although it has been glimpsed with telescopes for more than two centuries (it was discovered 129 years before Pluto), it has mostly appeared only as a small, fuzzy patch of light against the stars. We don’t know much about it, even though it is the only dwarf planet in the inner solar system and the largest body between the sun and Pluto that a spacecraft has not yet visited. We want to learn what it looks like in detail, what geological processes are taking place now or may have occurred in the past, what it is made of, and what that can tell us about the building blocks of the solar system. Ceres may have been in the process of growing to become a full-sized planet when Jupiter terminated its growth more than 4.5 billion years ago, so it may hold clues to the dawn of the solar system when planets were forming. There is reason to believe Ceres may have a substantial inventory of water. Most of it likely is in the form of ice, but it is possible there is a subsurface ocean of liquid water, and we would like to know more about that.
Exactly what work will you perform while there (i.e., what instruments will you use), and how long will you be there?
Dawn will take many pictures in black and white and in color, fully mapping this exotic world. It will map Ceres several times at different angles, effectively building up pictures in stereo so we can see the full three-dimensional shape of the alien landscape. Dawn will use four spectrometers as well: a visible mapping spectrometer, an infrared mapping spectrometer, a gamma ray spectrometer, and a neutron spectrometer. The first two will help reveal the chemical composition of the surface, indicating the kinds of minerals there. The last two will help establish the elemental composition, that is, what the atomic constituents are. By tracking Dawn’s orbital motion very, very precisely, we also will determine the distribution of mass inside Ceres to reveal its interior structure.
The measurements will be made from four different orbital altitudes, ranging from as high as 8,400 miles to as low as 230 miles. The spacecraft will spend as little as three weeks circling Ceres in some of the orbits and as long as three months in other orbits. It will use its advanced ion propulsion system to maneuver from one orbit to another, allowing us to change the orbit to optimize the measurements.
What happens to the spacecraft after that?
Dawn’s primary mission will end on June 30, 2016, but the spacecraft will remain in orbit effectively forever. If the spacecraft is healthy at that time and if NASA chooses to invest additional resources in it, Dawn many continue its exploration of Ceres for a while, but that is where it will stay when it ceases operating. I like to think it will become an inert deep-space monument to human ingenuity, creativity and our noble spirit of adventure. You can find more on the end of the mission and the spacecraft’s ultimate fate here.
Just how strong of a chance is there that Ceres once supported life? As strong as the chance on Mars, or are there attributes that make it less likely?
We simply don’t know enough about life or about Ceres yet to know how likely it is that life may have arisen there. We have indications there is water there, we know it has some heat (both from the distant sun and from the decay or radioactive elements deep beneath the surface), and there may also be supplies of the chemical elements needed for life. These may be necessary ingredients, but whether the recipe for life was completed on Ceres we just can’t say. Dawn does not have the capability to detect life, but it may help us understand the conditions better. Certainly this is among the places in the solar system that are potentially of greatest interest for life and its origins. As with other aspects of Ceres, I have more about this topic in my December Dawn Journal.