Latest look at Ceres, captured by Dawn's long range framing camera on 19 Jan 2015 from a distance of 238,000 miles courtesy of NASA/JPL
After traveling three billion miles for seven years with a stopover at Vesta, NASA's Dawn spacecraft is closing in on the dwarf planet, Ceres, a little world that has, up to now, been barely more than a point of light in our largest telescopes. We have to go back to the days of Voyager sailing through the moons of distant gas giants to appreciate just how much we might learn about the unknown landscape coming into view. The surface is mysterious because Ceres is small, just shy of 600 miles in diameter, almost as dark as charcoal in places, and it spends its time in the asteroid belt where the sun is many times fainter.
But the tiny world has a long, cherished history in astronomy. It was first discovered way back in 1801 by Giuseppe Piazzi and named after the Roman deity of agriculture, grain, and fertility. It has since been demoted from planethood, its classification argued over for decades, and recently re-admitted on probationary status as a dwarf planet. For the next few weeks, Ceres will remain the largest object between the sun and Pluto not yet visited by a spacecraft.
We don't have to wait much longer to see it! Join us below to discuss the mission and learn how the tiny little world coming in Dawn's view might play a big role in science and future space exploration.
Dawn was launched atop a three stage Delta II "heavy" on September 27, 2007, from Kennedy Space Center. Within a few weeks it had already lit up its ion-drive powered drives and headed off for its first encounter with the proto-planet 4 Vesta.
Those ion engines have performed brilliantly. Each nozzle spits out xenon ions at about 75,000 mph marked by an eerie blue plasma, almost an order of magnitude higher than conventional chemical propellants. The thrust is small, but ion engines can fire for years, giving this spacecraft an unparalleled ability to make in-flight velocity changes measured in miles per second. This may be the future of both manned and unmanned interplanetary exploration. New designs will have more thrust, more fuel, meaning those spacecraft would have the capacity to range around the solar system looking for objects of interest like virtual prospectors for decades on end.
Dawn is about the size of a large refrigerator box, weighing in at just over a ton, with two extended solar panels on each side to capture the fainter light of the sun in the main asteroid belt. The framing camera, well-proven after encounter with Vesta, will provide color, and black-and-white images—in fact, it has already begun. There are two spectrometers and a couple of particle detectors for teasing out data on the chemistry and and geology of Ceres. Those instruments have a big year ahead of them.
Hypothetical interior of Ceres. Click image for more info.
Ceres is a complicated, poorly understood world. It may seem like an oddball, but along with the larger trans-Neptunian objects like
Pluto and its cohorts, and zillions of smaller, icy bodies stretching clear from the main belt halfway to nearest star, it may be more representative of the stuff in our solar system than any body we have visited to date. It is a time capsule from the early formation of our solar system, a planet culled in embryonic development and preserved billions of years into the present for our study.
Despite its small size, Ceres is rounded by internal gravity, thought to have differentiated crust, mantle, and core, and sits near the frost line. Water on the surface would sublimate away, like dry ice on Halloween, but with just a little cover, it persists. If Dawn finds lots of subsurface water, little Ceres may have a big role to play in the long-term exploration and colonization of the solar system. Water is common in the inner solar system, and it exists here in huge oceans—on Mars as a sort of shallow mineral, even hiding from the sun inside crater rims on the moon.
Water is life, and it breaks down under abundant solar power into oxygen for breathing air and hydrogen for rocket fuel. It is one of the most valuable substance we can find and mine in space. Moving water from places like the Earth or the moon all the way to interplanetary orbit is difficult and expensive, to say the least. But Ceres has really low gravity, less than 3 percent Earth normal, and its day is only nine hours long. The high spin rate and low gravity means material from Ceres' surface would be incredibly cheap to move into space. A solid fuel rocket not much bigger than a coffee can would be able to loft big fat barrels into nearby synchronous orbit 500 miles above its equator.
In fact, the spin is so high and the gravity so weak that a full-blown space elevator could be made out of nylon rope. Find water, find other deposits like methane—heck, might as well wish for some handy metallic meteorites embedded here and there—mine them, build depots, and Ceres may one day be our grand central transfer station between the inner and outer solar system, a fertile beacon of life cruising the vast oceans of interplanetary space. What a perfectly poetic role for a dwarf planet named after an ancient goddess of agriculture and fertility.
For now we can only say the best telescope images suggest "some variation in features." There appears to be at least one or two distinct spots ... a recent crater gouged into a lighter subsurface of water or rock or glassy mineral? Some kind of upwelling from the interior ...?
We don't know! But what's so exciting is we will know in just a few weeks!