Space junkies try to explain mysterious image in photo from Mars rover

"A mysterious blotch that appeared along the
horizon in a photo from the surface of Mars
stirred speculation about what it might be,
as two hours later it was gone.

One image from the Curiosity rover as it
landed on the fourth planet from the sun
showed a "faint but distinctive" image on
the horizon, the Los Angeles Times reported.
However, a subsequent batch of images sent
from the unmanned rover two hours later
showed no trace of the blotch."

See:

http://news.yahoo.com/blogs/lookout/...190419541.html