Earlier this week, a strange silhouette appeared on one of the early pictures taken by the Mars Curiosity rover's Hazard-Avoidance Cams. Shortly after that picture was taken, the mysterious shadow was gone, causing a firestorm among conspiracy theorists worldwide.
The answer to the mystery was simple—and pretty cool too:
According to NASA, it was the impact plume created by the sky crane's crash on the Marian surface.
The images shown in this animated GIF were taken 45 minutes apart, which explains why you can see the impact plume on the first but it's gone on the second.