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Space/Science » in reply to re: Um. An optical illusion of what?

re: Um. An optical illusion of what?
Greg Orme — (archived)

Recently the MOC camera has been taking images more off nadir to save propellant. So it is conceivable that such a photo of geyser could be taken one day. But this image is described by MSSS as having an emission angle of .25 degrees, which makes it almost directly from overhead. If you take the height of the MOC above the ground and compare it to the length of the image, and get out the old cos and sine tables you'll see the angle is still almost directly above at all edges of the image.
I believe the image shows two streaks from each dot because the wind changes to those two directions in spring and autumn. Since it blows the same direction each year the streaks grow.
We cannot be seeing a side on view of a geyser from overhead any more than a spy satellite directly above your house can look in your windows.
For example put a pile of black dust on a board in a strong wind from the south and it will make a streak of the dust pointing to the north. Then if later another strong wind came from the west another streak would appear to the east and the north pointing streak would tend to curl in places to the east. So this then appears like the north pointing streak is a geyser bending in the wind and the east pointing streak is the material from the geyser. For some people the east pointing streak might appear like a shadow of the geyser but the sun angle is wrong.
Since it is well known that the wind on the pole can blow streaks from black dots all that is required is two wind directions at different times. If you look through martianspiders.com there are lots of examples there of streaks coming from dark dots like these.

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