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Satellite spots the remains of an ancient lake on Mars

A satellite orbiting Mars has discovered evidence that a giant crater was once a water-filled lake, scientists announced Friday.
Image: Martian craters
Mars' Holden Crater is 87 miles (140 kilometers) across, filling the left side of the image, while to the right is the remaining part of Eberswalde Crater, with a diameter of about 40 miles (65 kilometers). They are located in the southern highlands of Mars. North is to the right of the image. G. Neukum / ESA / DLR / FU Berlin
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A satellite orbiting Mars has discovered evidence that a giant crater was once a water-filled lake, scientists announced Friday.

Eberswalde Crater contains a rare case of a Martian delta. Channels which fed the lake in the crater are very well preserved. The delta deposits and channels together provide a clear indication of liquid surface water during the early history of Mars.

The rare find was revealed by the presence of a delta, where flowing water has deposited sediment in a characteristic fan shape.

The 40-mile-wide (65-kilometer-wide) crater is bone-dry today, but serves as another sign of Mars' wetter ancient past, scientists said. [See photos of Mars crater delta]

Ancient delta
The discovery was made by the European Space Agency's Mars Express satellite, which has been orbiting the Red Planet since 2003.

The delta is in Eberswalde Crater, in the southern highlands of Mars. The crater looks like a semicircular indentation on the right side of the image. Scientists think it was formed more than 3.7 billion years ago by an asteroid that slammed into the planet.

Only the right side of the crater is intact. The rest has been covered over by the larger Holden Crater, which was formed by a space rock that impacted later, kicking up debris that buried parts of Eberswalde. Holden Crater can be seen toward the left of the photo.

Watery past
Enough of Eberswalde was preserved, however, that the telltale forms of the 44-square-mile (115-square-kilometer) delta can be seen. Near the top of the crater, the thin, squiggly lines represent feeder channels that would have carried water and sediment.

Overall, the delta features paint a picture of a once-full lake filling the crater, providing clear signs that the surface of Mars once flowed with liquid water.

Both Eberswalde Crater and Holden Crater were originally candidates for the landing site of NASA's next Mars rover, Curiosity. The rover, which will launch in November, will look for signs that Mars used to be habitable. Ultimately, Eberswalde and Holden were passed over for Gale Crater, which boasts high amounts of minerals and possible signs of past water.

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