Changes at Low Ridge Haven |
Changes at Low Ridge Haven |
Sep 18 2006, 04:56 PM
Post
#1
|
||
Senior Member Group: Members Posts: 4252 Joined: 17-January 05 Member No.: 152 |
It's been pretty slow in the Spirit forum recently, but hopefully this will reawaken it.
A new thin dark streak is visible in the latest sol 961 rear hazcam, that wasn't visible in the previous shot, from sol 924. It's visible in both L and R hazcam views. It looks remarkably like a dust devil streak, but the scale is very small. Here's the R hazcam from sol 894 subtracted from the 961 image: The dark streak cuts across more or less from left to right about a third of the frame down from the top. Other differences are visible, mostly around rocks, due to the change in sun angle between the frames. To demonstrate that the dark streak isn't just an effect due to that change in sun angle, look at these three frames: sol 856, local time 11:07 sol 961, local time 11:21 sol 894, local time 11:45 You can see that the shadows move progressively from the sol 856 to 961 to 894 frames above, as you'd expect from the local times they were taken. But if you flip between the three frames, you can see the dark streak only in the middle (sol 961) frame. If the streak were due to changing sun angle it would be at least as strongly visible in the 856 or 894 frame. Therefore it's not due to sun angle. As I said, this is way too small for a dust devil streak. And, I don't think we're anywhere near dust devil season. My guess about the origin of this is a small "crumble event" on one of those dark rocks in the upper left, followed by the normal winds blowing some dark dust downwind. Anyone know if the streak direction is consistent with what the winds should be doing now? Has anyone else noticed changes near Spirit? |
|
|
||
Sep 18 2006, 06:29 PM
Post
#2
|
|
Senior Member Group: Members Posts: 4252 Joined: 17-January 05 Member No.: 152 |
Doug, the local time difference between the sol 856 and 961 frames is 14 minutes, which corresponds to a solar angle change of just 3.5 degrees. For sols 961 and 894, the difference is 24 minutes, or 6 degrees. The change in solar panal shadows looks quite large because of the height of the panels above the ground and the closeness of the panel shadows to the hazcam. 3.5 degrees is not a lot of change!
But the strongest argument that the dark streak is not the result of the change in sun angle is in my third from last paragraph in my post above! Any such putative darkening of a patch of soil due to changing solar angle must be monotonic with that angle over such a small range of angles, whereas my three frames show that it clearly is not. Notice also that the dark streak crosses areas of ground that are at different inclinations, due to ripples etc. Why would differently oriented patches of surface respond to changing solar angle in the same way? Look for example at the largest rock closest to the rover (pixel location 680x375 or so). There are large variations in surface inclination angle in the soil surrounding it, but these do not show up in my difference image - the entire area (except for the rock's shadows) is very close to uniform on the difference image. Also we don't see any other such darkened (or lightened) patches of soil elsewhere. Just one curiously linear darkened patch. Finally, the dark streak is darkest at the left, near my putative source, and thins to the right. Altogether, an argument that the streak is an illumination feature necessarily takes on a conspiratorial character: differently oriented patches of soil, coincidentally lined up in a streak, responding in a bizarre non-monotonic way to small changes in solar angle. Edit: that's conspiratorial in the sense of "contrived", of course no-one's conspiring here! Actually there is another simple explanation: the feature is the shadow of something off the frame to the upper right. But that's even more conspiratorial! |
|
|
Sep 18 2006, 06:56 PM
Post
#3
|
|
Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
Any such putative darkening of a patch of soil due to changing solar angle must be monotonic with that angle over such a small range of angles, whereas my three frames show that it clearly is not. Actually the change in solar elevation angles are even less than you indicate because of the change in noon solar elevation as she passed through mid winter. Also there is also a change in solar azimuth that might have been relevant had the solar elevation angle been low enough to cast shadows from landscape features off to the left. It isn't and as you point out anything that could cause such a shadow would be really conspiratorial. Sol 856 LT 11:07 - Elevation 53.5deg Az 3.9deg Sol 961 LT 11:21 - Elevation 50.7deg Az 351.7deg Sol 894 LT 11:45 - Elevation 49.5deg Az 347.0deg I cannot see how you would get an area of shadow across the entire region in question that would only appear on Sol 961. We still need another photo to be sure but it does look like a clear change to me. |
|
|
Lo-Fi Version | Time is now: 13th June 2024 - 01:12 AM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |