[X] My Assistant

[Guest_AlexBlackwell_*]

Two papers announcing new results of observations of Mars' south polar cap, Langevin et al. and Kieffer et al., are being published in the August 17, 2006, issue of Nature. See the Editor's Summary for a brief synopsis and links.

[djellison]

They don't suddenly disappear.

And if they did - why would that suggest that the people who built the camera and have operated it for nearly a decade have got the illumination angle wrong by 90 degrees?

If these were features of any height, we would see shadows extending down and to the right much as we do with dust devils...

http://www.msss.com/mars_images/moc/2006/07/17/
http://www.msss.com/mars_images/moc/2006/07/05/
http://www.msss.com/mars_images/moc/2006/06/08/
http://www.msss.com/mars_images/moc/2006/03/16/
http://www.msss.com/mars_images/moc/2006/01/20/

We don't see that. We do, however, see streaks that point not in the direction we would expect a shadow, but in the direction of the prevailing wind. The artists impression is a best, a huge dramatisation and at worst, complete fiction.


Doug

[mcaplinger]

And if they did - why would that suggest that the people who built the camera and have operated it for nearly a decade have got the illumination angle wrong by 90 degrees?

Hey, we're not infallible. The "image of the day" release lighting direction could be wrong (I don't think it is, but it might be.) But the official PDS release on our Web site is pretty carefully computed and checked, so somebody should feel free to look at the images in question there and confirm that the lighting is as stated in the "image of the day" release.

I think it's a pretty safe bet that if there was anything remarkable in these images somebody at MSSS would have seen it, but I'm happy to keep an open mind about it.

[edited: I think the claim is that we got it wrong by 180 degrees, not 90 degrees ]

[mcaplinger]

Hey, we're not infallible. The "image of the day" release lighting direction could be wrong (I don't think it is, but it might be.) But the official PDS release on our Web site is pretty carefully computed ...

OK, I've checked the situation and it's a bit more confused than I wish it was. As has been discussed before, the definition for the cumindx.tab entry for SUN_AZIMUTH depends on a left-right "flip flag" in one of the other fields and is defined relative to the image that appears on the PDS archive volume. I had been under the impression that the "processed but not map-projected" version of the image in the MOC Gallery was identical to the PDS image, but it turns out that they are being rotated in some manner (at least for the more recent releases), but the SUN_AZIMUTH parameter is not being adjusted appropriately. I'm going to check to see if the people in charge of the gallery can clarify this situation. In the meantime the official PDS release is correct, which is the important thing.

That said, I checked image S08-00321 and the sun direction is as it says in the "image of the day" release, so I don't see how those dark streaks could be the shadows of geysers.