Dawn approaches Ceres, From opnav images to first orbit Options

[Phil Stooke]

On Tuesday (two days from now, for visitors from the future), the first optical navigation image will be taken... hopefully we'll have it in our hands soon after that. So it's time for a new topic. Over the next few months we'll have progressively closer images and full orbit characterization sequences, no doubt including multispectral image sets.

A new world...

This is a bit of reprocessing I have been doing with the Hubble images from a few years ago.




Phil

[nprev]

Certainly some fascinating speculation on the thread so far. Rather unusual to have a mystery like this persist for this long after a first encounter, I think, but that's undoubtedly a consequence of Dawn's approach & orbital capture trajectory requirements.

The only conclusion I feel safe to make is very generic: Whatever it is, it's young, and I mean like thousands of years old maybe; I'd guess younger than that.

My rationale is that there seems to be only one of these regions on Ceres, and it's tiny. (Okay, two close together but REAL close, so almost certainly associated.) There are other geological provinces of sorts, but all of far greater extent. In turn, to me this argues for an exogenic origin since an endogenic process would likely not be confined to such a small area of this body.

In fact, and please correct me if I'm wrong, on every object we've examined with current active surface processes (volcanic or not) said processes are distributed across broad regions of the body. Iapetus' albedo process is global, Enceladus' geysers are regional but across a proportionally large area of the moon's surface, Titan's seas are polar.

Therefore, I'm putting my money on a VERY fresh pair of impact craters that have exposed underlying ice. That may well be sublimating when exposed to direct sunlight just like a comet's ices do, but that's the extent of activity.

Pure luck that this happened before Dawn arrived is all. If this model is correct, Ceres must periodically sport relatively dazzling bright spots until they are covered by either Sun-induced darkening of organics or dust from other impacts.

[Ken2]

Therefore, I'm putting my money on a VERY fresh pair of impact craters that have exposed underlying ice. That may well be sublimating when exposed to direct sunlight just like a comet's ices do, but that's the extent of activity.

MOD NOTE: Full inline quote edited to point of discussion.

I agree completely - it is very unlikely that only one spot on the entire dwarf planet would have a volcano / geyser / oozing ice etc, where as craters in bigger craters are all over the place - we would expect a few young craters on a body of this size.

To help visualize the white spot fitting an impact crater I took a similar crater within a crater and used a moon simulator to watch it's brightness change as a function of phase angle - as you can see it is entirely consistent with the white spot picts seen to date.

MOON: (click to see animated GIF)



CERES:



Finally on another note: as to the central peak types of ideas for the white spot - I don't see any convincing central peaks on Ceres - they look like they are secondary crater caused with a couple that are questionable - but if 90+% clearly don't have them, it is highly unlikely any do.

[Gerald]

... I don't see any convincing central peaks on Ceres ...

Light from left, near the terminator, examples and schemes: