Planetary scientists at the European Space Agency have released 3D images of the "striking upper part of the Reull Vallis region of Mars", which reveal a 1500km long river running from the Promethei Terra Highlands to the vast Hellas basin.
The river was is huge. The image data from ESA's Mars Express spacecraft shows that, at some points, the river bed is 7km wide and 300m deep. The stereo cameras on board the satellite have also revealed "numerous tributaries" that fed the gigantic river.
On the right of the images you can see the Promethei Terra Highlands's mountains, "rising around 2500m above the surrounding flat plains". A spectacular landscape not very different from many on Earth.
Just like Earth
The ESA Mars Express team says that the river was flowing with abundant water about 3.5 to 1.8 billion years ago, during the Hesperian period. After that, the Amazonian era started, causing the Reull Vallis to be invaded by a glacier. This glacier carved the valley where the river was, pushing debris and ice, and causing the sharp sides you can see in these images.
Together with all the data gathered by NASA and ESA robots and probes, it's obvious that Mars suffered the same geological process we had here in our little blue planet:
These analogies are giving planetary geologists tantalising glimpses of a past on the Red Planet not too dissimilar to events on our own world today.
The researchers think that Reull Vallis is just like any glacial valley on Earth -- like the one you can see at Yosemite but without trees and tourists. At one point, Mars may have very well looked like this:
Much later, meteors impacted on the valley's surface, causing the craters you can see in the image. Scientists believe that craters and other geological features in the area may be full of ice water.
Top view in natural colour.
A perspective view, with one of the tributaries connecting to the gigantic river in the middle.
The arrows point at the main river and one of the tributaries.
A beautiful view.
If you have stereo anaglyphic glasses, you can see this in 3D.