[X] My Assistant

[remcook]

Paper out tomorrow: http://www.bbc.co.uk/news/science-environment-25849871
Very exciting that we will visit this world soon!

[Doug M.]

An interesting question I haven't seen addressed: what's happening to the water?

Obviously most of it is being lost to space. But even with Ceres' weak gravity, you'd expect some water to recondense at "cold traps" -- cooler spots on Ceres' surface, i.e. in shadowed crater bottoms and at the poles. The technical term for this is "volatile transport", and we see it in some other places in the Solar System, like Jupiter's moon Callisto. (That's why all the impact craters on Callisto's icy surface look slumped and eroded.) If even 1% of the water vapor were to be recaptured, it would accumulate in the polar regions at a rate of a micron or two per year. That may not sound like much, but over astronomical time you'd see meters of accumulated condensation.

But we don't see that. Ceres is a very dark body (its albedo is around 0.06, almost as dark as fresh asphalt) and water frost is bright. There are lighter patches on Ceres, but there don't seem to be bright ice caps at the poles.

In a little while we'll know more. Patience...


Doug M.

[dvandorn]

Speaking of behaviors of processes over astronomical timeframes always runs the risk of ignoring the nature of relatively short-term phenomenah which occur in bursts and blurps. (For example, the overall process of accretion over a 4.6-billion-year period resulted in the Earth-Moon system, but the day of the Big Whack created, in mere hours, the conditions resulting in the current system, its angular momentum, Earth's rotational period, etc.)

If non-homogeneous concentrations of volatiles exist within Ceres' outer crust, maybe water ice spurts and sublimates for a few thousand years and then stops, then later methane ices do the same thing over a few thousand years, etc. Each episode of volatile transport would have its own effect on the surface coatings at the poles and in other cold traps, depending on the specific volatiles being transported and how they react to sunlight and radiation over time, etc.

Ceres being so much closer to the Sun than the Jovian and Saturnian moons, it's hard to make direct comparisons, but it's possible that Ceres has (or had) a wider range of volatiles than the moons we've observed, and definitely sees a higher solar constant than do the outer planet moons. These would seem to be important factors, too.

As you say, though, much will become more clear as we approach Ceres with Dawn and get some of the hard data that will let us answer some of these questions.

-the other Doug