A mysterious photograph of a bright, crumpled object on Mars taken by the Curiosity rover has caused controversy, after some dubbed it a "Martian flower".
The shiny, white object was pictured embedded in a rock, in an image taken by the Mars Hand Lens.
It was captured on 19 December, and went largely unremarked until users of an online forum claimed it looked like a "flower".
"Flower? My first thought was crystal. Could be a life-form. It looks sort of squishy," said one user of Above Top Secret.
Others said it was more likely to be a piece of plastic from the rover itself: another similar object was explained in this way back in October.
But Nasa disagreed with both theories in this case, and said that the transparent object was likely to be part of the rock - possibly a mineral dump of some sort.
Meanwhile, another picture from the planet also caused excitement - followed by mild disappointment - after picturing a formation named "Snake River", though it too offered no evidence of life on the desolate dry Martian surface:
The picture shows a thin and long line of curving rock, like a small ridge.
Nasa said it might make a good place for Curiosity to investigate.
"It's one piece of the puzzle," said rover mission project scientist John Grotzinger.
"It has a crosscutting relationship to the surrounding rock and appears to have formed after the deposition of the layer that it transects."
The $2.5 billion rover is set to start drilling for the first time next week, six months after landing on Mars.