U. COLORADO (US)—The discovery of the first evidence of shorelines on Mars indicates the presence of a deep ancient lake and past life on the Red Planet, say researchers from the University of Colorado at Boulder.
“Finding shoreline is a Holy Grail of sorts for us,” says Brian Hynek, assistant professor in the geological sciences department, who worked with research associate and study leader Gaetano Di Achille.
Estimated to be more than 3 billion years old, the lake appears to have covered as much as 80 square miles and was up to 1,500 feet deep—roughly the equivalent of Lake Champlain that borders the United States and Canada, Di Achille says. The shoreline evidence, found along a broad delta, includes a series of alternating ridges and troughs thought to be surviving remnants of beach deposits.
“This is the first unambiguous evidence of shorelines on the surface of Mars,” says Di Achille. “The identification of the shorelines and accompanying geological evidence allows us to calculate the size and volume of the lake, which appears to have formed about 3.4 billion years ago.”
A paper on the subject by Di Achille, Hynek, and CU-Boulder research associate Mindi Searls, all of the Laboratory for Atmospheric and Space Physics, has been published online in Geophysical Research Letters.
Images used for the study were taken by a high-powered camera known as the High Resolution Imaging Science Experiment, or HiRISE. Riding on NASA’s Mars Reconnaissance Orbiter, HiRISE can resolve features on the surface down to one meter in size from its orbit 200 miles above Mars.
An analysis of the HiRISE images indicate that water carved a 30-mile-long canyon that opened up into a valley, depositing sediment that formed a large delta. This delta and others surrounding the basin imply the existence of a large, long-lived lake, located within a much larger valley known as the Shalbatana Vallis, says Hynek.
In addition, the evidence shows the lake existed during a time when Mars is generally believed to have been cold and dry, which is at odds with current theories proposed by many planetary scientists, he says. “Not only does this research prove there was a long-lived lake system on Mars, but we can see that the lake formed after the warm, wet period is thought to have dissipated.”
Planetary scientists think the oldest surfaces on Mars formed during the wet and warm Noachan epoch from about 4.1 billion to 3.7 billion years ago that featured a bombardment of large meteors and extensive flooding. The newly discovered lake is believed to have formed during the Hesperian epoch and postdates the end of the warm and wet period on Mars by 300 million years, according to the study.
The retreat of the lake apparently was rapid enough to prevent the formation of additional, lower shorelines, says Di Achille. The lake probably either evaporated or froze over with the ice slowly turning to water vapor and disappearing during a period of abrupt climate change, according to the study.
Because deltas on Earth rapidly bury organic carbon and other forms of life, the Mars deltas are of high interest to planetary scientists. Most astrobiologists believe indications of life on Mars will be discovered in the form of subterranean microorganisms. Lakes on Mars would have provided cozy surface habitats rich in nutrients for such microbes, Hynek says.
Di Achille says the newly discovered pristine lake bed and delta deposits would be would be a prime target for a future landing mission to Mars in search of evidence of past life.
“On Earth, deltas and lakes are excellent collectors and preservers of signs of past life. If life ever arose on Mars, deltas may be the key to unlocking Mars’ biological past.”
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