The faint but distinctive dot which can be seen on the horizon of the Red Planet was taken by a device on the $2.5 billion robot called its Hazcam and relayed by the Mars Reconnaissance Orbiter back to Earth.

However, two hours later when the satellite made another pass over Curiosity, the rover sent another batch of images that revealed that the blotch had eerily disappeared.

The Internet was instantly awash with theories as to why the two photographs would be different, especially as the rover, which is the largest spacecraft ever sent to another planet, landed on its own with no direct control from NASA mission control.

Furthermore, the rover was acting autonomously, meaning that scientists did not command the robot to photograph the exact views containing the blotch.

The most prominent reason discussed online for the mysterious blot is that Curiosity managed to photograph over the course of 200 milliseconds the crash-landing of the spacecraft that carried the rover to the Martian surface.

************************************************************************************

The blotch did look like a billowing plume of some sort, erupting from the horizon. But the image "would be an insane coincidence," one engineer said. Most dismissed the chatter as wild-eyed speculation and a statistical impossibility. It was just dirt on the lens, some said — maybe a dust devil swirling in the distance, but nothing more than that.

Yet a pesky fact remained. In the first photo, the blotch is there. "And then it's not," said Sarah Milkovich, a scientist at the Jet Propulsion Laboratory in La Cañada Flintridge and a leader of the team responsible for delivering images documenting the mission.

Excerpts above from The Daily Mail and the Los Angeles Times.