Dawn approaches Ceres, From opnav images to first orbit |
Dawn approaches Ceres, From opnav images to first orbit |
Jan 12 2015, 12:10 AM
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Solar System Cartographer Group: Members Posts: 10227 Joined: 5-April 05 From: Canada Member No.: 227 |
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 -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PDF: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Mar 4 2015, 11:46 PM
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#2
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Member Group: Members Posts: 716 Joined: 3-January 08 Member No.: 3995 |
A possible process of producing straight valleys on Ceres....
Ceres' oblateness and density have been interpreted as evidence of an icy envelope around a rocky core. What then would have happened to the relatively brittle crust above the plastic/fluid mantle as Ceres transformed into an ellipsoid? Longitudinal cracks should have formed (I think) as tensional forces stretched the equator: Grabens may have formed as some blocks were displaced: (Dimensions and extent of features are not necessarily to scale.) In recent imagery, there seem to be some longitudinal valleys (grabens?) in a few places, but they are pretty degraded. It would be interesting to see if there is (more) evidence of a fracture pattern as Dawn moves in for a closer look. Of course this process may be completely wrong; I'm just trying to make sense of what we've seen so far. |
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Mar 5 2015, 04:23 PM
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
Ceres' oblateness and density have been interpreted as evidence of an icy envelope around a rocky core. What then would have happened to the relatively brittle crust above the plastic/fluid mantle as Ceres transformed into an ellipsoid? This assumes that Ceres started out a sphere with the same spin rate it has now, or that it spun up for some reason. But there's no reason to assume either of those things. Icy moons of giant planets are thought to have experienced forces like this because they would have started out spinning relatively fast (like Ceres does now), and then spun down as a result of tidal forces until they reached their present-day rotation rates, becoming more spherical in the process -- it causes global compression at the equator and extension near the poles. But there are no tidal forces on Ceres so you wouldn't get tectonics related to despinning. Now one thing that can cause global tectonics on a body that lacks moons or a planet is global reorientation. If you have a body like Ceres (or Mars!) that experiences a big impact or major volcanic event that causes a major shift in the center of gravity, the spin axis may reorient to a more stable position, putting excess mass at the equator. That may have happened to center the Tharsis province across the equator at Mars. The preexisting rotational bulge would then be in the wrong position, and spin-related stresses would act to reshape the planet to match the new location of the spin axis. -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Mar 5 2015, 05:22 PM
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#4
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
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