Dawn's first orbit, including RC3, March 6, 2015- June 15, 2015 |
Dawn's first orbit, including RC3, March 6, 2015- June 15, 2015 |
Mar 6 2015, 03:23 PM
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Member Group: Members Posts: 204 Joined: 14-April 06 From: Seattle, WA Member No.: 745 |
Dawn is now officially in orbit around (1) Ceres!
Congratulations, NASA. Nice images of crescent Ceres. NASA Spacecraft Becomes First to Orbit a Dwarf Planet |
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Apr 21 2015, 02:00 AM
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#2
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Junior Member Group: Members Posts: 68 Joined: 27-March 15 Member No.: 7426 |
Dr. Chris Russell, principal investigator of the Dawn mission, indicated in an e mail today to NBC News that even at the current resolution (
NBC News Article |
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Apr 21 2015, 03:37 PM
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#3
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Senior Member Group: Members Posts: 4247 Joined: 17-January 05 Member No.: 152 |
Dr. Chris Russell, principal investigator of the Dawn mission, indicated in an e mail today to NBC News that even at the current resolution (1300 meters/pixel) the bright spots were not resolved. It probably depends on exactly what you mean by "resolved". There's certainly not much detail visible in both of the two spot 5 subspots, but I would call them "resolved" in the sense that they are clearly larger than the PSF. Both of the subspots are elongated, and the orienation of elongation rotates with Ceres. This means the elongation can't be due to bad optics (eg, astigmatism) and almost certainly not due to motion blur during the exposure. Similarly, it is extremely unlikely for pixel noise to conspire to produce elongation in both subspots rotating consistently with Ceres's rotation, even though we're looking at only a small number of pixels here (ie, S/N looks good judging from frame-to-frame consistency).It appears that the fainter subspot (upper in my animation below) is composed of two "sub-subspots" (again, the consistency from frame to frame argues against pixel noise). The brightest subspot (lower in my animation) perhaps also consists of two sub-subspots, the lower of which appears first and the upper which brightens. As others have pointed out, these sorts of brightness variations could be simply due to variable geometry of exposed surfaces/shadowing. |
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Apr 21 2015, 06:25 PM
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#4
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Junior Member Group: Members Posts: 68 Joined: 27-March 15 Member No.: 7426 |
It probably depends on exactly what you mean by "resolved". There's certainly not much detail visible in both of the two spot 5 subspots, but I would call them "resolved" in the sense that they are clearly larger than the PSF. I recall when only one bright spot was discernible in this crater, then there were two. There was apparently no claim that the spot had been optically resolved at this point. When Dr. Russell says that the spots are not resolved because they're too small, I'm inclined to rely on that, given his expertise, and knowledge of this particular situation. It does not appear to me that the brighter of the two spots is even separated into two distinct parts, which seems to argue against any reasonable definition of the word 'resolved'. The variable lighting of portions of this spot could have any one of several explanations. The bright spot sometimes appeared to be elongated in the images, long before there was any thought that it might be optically resolved. ADMIN NOTE: Everyone - I think that we can drop the discussion over the word 'resolved'. You can go into the 'micron' scale and still not fully "resolve" an object. Let's just wait for better images that will help to identify the nature of these features. Not long now. |
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