Ceres (pronounced “series”) is in the asteroid belt — but it’s not just an asteroid. Technically, Ceres is also a dwarf planet (the only one inside the orbit of Pluto), making it an improbable body that’s of immediate interest to astronomers. Jets of what looks to be water vapor have been spotted, sparking the same speculation about alien life that extra-terrestrial water always does. It’s unlikely Ceres holds life, but as both an asteroid and a planet it could offer unique insights into the history of the solar system. As of a few months ago, it was also the site of a major astronomical mystery — and today, mankind finally arrives.
The Dawn spacecraft is scheduled to arrive at Ceres today, carrying a scientific payload that was previously trained on the second largest object in the asteroid belt, called Vesta. Using its pioneering ion propulsion system, which provides low, constant thrust with remarkably little onboard fuel, Dawn was able to not just perform a flyby, but bump itself into a stable orbit. Soon, Dawn’s ion thrusters will direct it into a similar spiral around Ceres, making it the first ever multi-target mission to enter a stable orbit around two different objects in deep space.
A tentative layout of the interior of Ceres.
Once in orbit, Dawn will spend several weeks spiraling down to its “science orbit,” from where it will be able to take detailed surface readings with its multiple scientific payloads. Primarily, it will build a map of the surface of Ceres in the visible and infrared portions of the spectrum and look at the chemical composition of the surface rocks — but of course the real main question has to do with the Ceres mystery: why does the dwarf planet have bright spots?
This is something astronomers first noticed several months ago: There seemed to be a well-defined bright spot on the surface of Ceres. Closer inspection revealed that it is actually twobright spots, both apparently located at the bottom of a major crater. This led some to speculate that they might be cryovolcanoes, planetary pimples that spew frozen substances rather than molten ones, but NASA believes the spots may be even more important than that. The official theory is the bright spots are actually static reflections of the Sun’s light, and probably arise from either ice or salt fields.
Why is that important? Because water is the primary substance we associate with life. Ceres has long been thought to harbor a subterranean ocean, and these bright spots might mean that some ancient meteor actually blasted down to give us a clean view of the frozen surface. On the other hand, these could be enormous fields of reflective salt crystals, which would be equally amazing in its own way. The spots could even be caused by large amounts of exposed metals, though if we do find some wonderful ore deposits, we’ll be able to do little more than drool over them. An extended mission to Ceres would probably only be possible if launched from a Mars station.
These sorts of visualizations of the asteroid belt are nonsense; these objects are actually separated by thousands of kilometers.
Ceres is so massive that it probably maintains a very thin atmosphere of its own, but perhaps more impressive is that it is also the only asteroid known to have been rounded by its own gravity. The rock and metal that makes up the planets can actually be quite malleable over millennia. The main reason most asteroids tend to be oblong is that they aren’t heavy enough to exert enough gravitational force to make their own rocky structures flow. Ceres presents a nice surface for science (and perhaps someday visitation) because its life history means it doesn’t have nearly so irregular a surface.
The scientists from NASA’s Jet Propulsion Laboratory are excited to solve the bright spot mystery, but they are equally excited to start uncovering the more general secrets of the most exotic super-asteroid known. While the bright spots mentioned above probably aren’t cryovolcanoes, Ceres might still very well have them, and they might help explain the overabundance of water vapor in certain areas of the surface. The heavenly body is absolutely packed with secrets to uncover, and now Dawn is finally about to start.
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