Dawn approaches Ceres, From opnav images to first orbit Options

[elakdawalla]

Chitchatting with other people here at the New Horizons science team meeting, I think it's true to say that many here would be surprised if some of the features we're looking at did not turn out to be craters. However, there are also a lot of spots that look weird that everybody's on the fence about whether they are craters or albedo markings, and we'll just have to wait and see. Jan 26 images will have resolution twice as good.

[MarkG]

Spectacular pictures! Wild cheering from the bleachers...!

[Bjorn Jonsson]

It's interesting that even though the resolution of these images is a bit lower than HST's, the higher phase angle apparently partially 'compensates' for that by making topography easier to see near the terminator thanks to what are probably shadows/topographic shading. I see hints of probable big craters. Also elongated features but I'm not sure whether they are ridges, depressions, albedo features or some combination of these. It will be very interesting to see the January 26 images; they should provide some answers.

[elakdawalla]

Bjorn, what you said is pretty much what the New Horizons geology and geophysics team said about these images

[dvandorn]

These images, and especially the animation made from them, do give the impression of a cratered body. In much the same way that the early Mariner 10 images gave the impression of a cratered Mercury -- very suggestive, but not enough to say for sure.

Of course, we would most definitely expect Ceres to be cratered -- with no tidal "pumping" I can't conceive of a heat source (internal or external) that would result in ongoing re-surfacing, and every other airless body that lacks an internal heat source (i.e., pretty much all of them except Io, and to a lesser extent Europa and Enceladus) that we've looked at in our solar system has been heavily cratered. Even Enceladus has some heavily cratered terrain far away from its active plumes. It would be the scientific discovery of the decade were Ceres not heavily cratered.

The one nice thing we can say is that we don't have very long to wait, in the overall scheme of things, to get a much better look at this dwarf planet. The Hubble suggestions of an almost Mars-colored world have had me intrigued for quite some time. Now we are very near to knowing, if not the whole truth of the matter, then at least enough data to raise questions we don't even know enough to start asking yet.

-the other Doug

[Guest_alex_k_*]

An attempt to process raw image, x8, details are exaggerated:


For comparision processed version from NASA in the same size:

[Fran Ontanaya]

Very crude attempt at overlaying HST and Dawn

[Habukaz]

Of course, we would most definitely expect Ceres to be cratered -- with no tidal "pumping" I can't conceive of a heat source (internal or external) that would result in ongoing re-surfacing, and every other airless body that lacks an internal heat source (i.e., pretty much all of them except Io, and to a lesser extent Europa and Enceladus) that we've looked at in our solar system has been heavily cratered. Even Enceladus has some heavily cratered terrain far away from its active plumes. It would be the scientific discovery of the decade were Ceres not heavily cratered.

Could not Ceres having formed "alone" compared to the icy satellites of the gas planets who formed right next to giants have an impact on, say, local distribution of radioactive isotopes (and heavier elements in general)?

[Phil Stooke]

There was so much mixing going on that the difference in location might not make much difference, regarding distribution of isotopes. However, dvandorn's point about cratering overlooks relaxation as a way of removing craters. Ceres is warmer than Callisto and its ice might have relaxed more. Recent studies have been suggesting that craters would be found near the colder poles, but would be flattened - maybe resembling palimpsests on Ganymede if not lost completely - at lower latitudes.

http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1798.pdf

http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1655.pdf

http://levee.wustl.edu/~mbland/pubs/Bland_13.pdf


Here is a rough reprojection of the new Ceres images. VERY rough. The registration is not very good. Proper maps will be produced by the Dawn team. This is just to start to show what a map might look like. So positions can't be counted on for high accuracy. I compare it with the HST map (EDIT - replaced map with a properly aligned one - also improved the registration of the HST map).

Phil

[TheAnt]

The Hubble suggestions of an almost Mars-colored world have had me intrigued for quite some time. Now we are very near to knowing, if not the whole truth of the matter, then at least enough data to raise questions we don't even know enough to start asking yet.

The orange material on the surface that is of huge interest to some of us, though it might have been somewhat changed by sunlight and radiation, it might be quite more pristine than the material we have gotten a glimpse of at Titan, which is heavily reprocessed.

Habukaz:
Could not Ceres having formed "alone" compared to the icy satellites of the gas planets who formed right next to giants have an impact on, say, local distribution of radioactive isotopes (and heavier elements in general)?

It is the current thinking that a world like Ceres indeed formed on its own, the question is how it is related to the other large asteroids.
Were those once more similar to Ceres in the past? And lost their surface layers by collisions, which Ceres simply were lucky to escape.
Or is Ceres one interloper, that somehow have gotten the orbit circularized in the asteroid belt. I consider the latter less likely, but mentioned for completeness since it has been suggested.

Internal heating by radioactive decay is of course possible, but remember this is a miniature world, and after aeons after formation the activity would be very low with correspondingly rather little heat. There have been some suggestion that serpentinization of minerals might be a heat source that could keep water liquid close to the core. I am personally pessimistic, but for DrShank's and his colleagues sake I hope to be proven wrong, it could make his work more interesting. =)

And thank you all who posted images of the first glimpse of one intriguing little world. =)

[elakdawalla]

I assumed that the flickering of the animation was due to filter wheels, but it turns out they're all clear-filter images, and the flickering is due to lack of calibration. So don't be tempted (as I was) to try to turn them into color pictures!

[Astroboy]

Can we call the faint smudge the Little White Spot, in the tradition of Jupiter and Neptune?

[Phil Stooke]

I edited my map comparison, just above, to correct the positioning of the Dawn images. I replaced the image, but I thought an additional post might be a good idea to draw attention to the change in case anyone downloaded the bad version.

Phil

[Gladstoner]

So far it reminds me of Umbriel.

[dvandorn]

Could not Ceres having formed "alone" compared to the icy satellites of the gas planets who formed right next to giants have an impact on, say, local distribution of radioactive isotopes (and heavier elements in general)?

AIUI, planet formation theory would have it that metals get less and less common in the original protoplanetary disk as you moved away from the Sun, reflected in the relative abundances of metals in the planets as you move outwards.

I have also heard theories that Jupiter once orbited much closer to the Sun, approximately where the asteroid belt is now located, while Saturn was created approximately where Jupiter is now located. As we have seen happen in other solar systems, Jupiter began to migrate closer to the Sun and supposedly began to draw off materials that ought to have contributed to the overall mass of Mars (resulting in Mars ending up smaller and less massive than would otherwise have been expected), but that before Jupiter could move far enough in to begin to disrupt the formation of Earth or any of the other inner planets an orbital resonance with Saturn began pulling it back away from the Sun, in the process tossing Saturn much farther out and likely tossing Neptune out past Uranus.

This all could have affected the formation of Ceres by disrupting its formation at a critical time, such that Ceres had a much larger amount of mass taken away from it by Jupiter. The square-dancing swing-arounds that reorganized the outer planets could also well have been responsible for tossing Ceres into its current, somewhat-skewed orbit -- meaning it could have been a planetesimal that had been forming closer to the Sun than its current location, and thus more enriched in metals than the moons of the outer planets. But it was far enough away from the Sun by the end of its creation that it accumulated a lot of snowballs near the end, accounting for its (potential) resemblance to the icy moons of Jupiter and Saturn.

However, in terms of radioactive heating, most of the planetary formation theories I've read point at Aluminum-26 as the major heat producer in the cores of the inner planets during their early histories. AL-26, however, has a relatively short half-life after it is created in a supernova, so the heating would have contributed only to the initial melting of the rocky planets' cores. None of the other radioactive heat-producing elements that survive to modern times could be contained in great enough quantity in such a small body as Ceres to create a hot core that would have persisted to modern times.

-the other Doug