There seem to be 2 new “gully” sites with light toned markings on the surface that suggest that liquid water has flowed as recently as within the past 7 years on Mars. The smoking gun is revealed in earlier images taken of the same region with these details not present and this is what gives NASA the time frame of 7 years.
![Gullies Before and After on Mars](http://static1.squarespace.com/static/5aeb2d61ec4eb71db6368339/5c35b5e02483d60902134b5f/5c35b8cc2483d6090213d034/1547024588737/gulliesbeforeandafter.thumbnail.jpg?format=original)