NASA Images Add a Billion Years to Mars's Wet Period?

Anne Minard
for National Geographic News
September 26, 2008

Recent high-resolution images taken by NASA's Mars Reconnaissance Orbiter suggest Mars may have stayed wet a billion years longer than most previous estimates, scientists report.

Researchers say they have identified water-carved features that date to the Hesperian Epoch, 3.7 to 3 billion years ago.

The time frame is far more recent than the period scientists most often associate with the presence of liquid water on Mars—the Noachian Epoch, which spanned the first billion years on the red planet from about 4.6 to 3.5 billion years ago.

Catherine Weitz is a senior scientist with the Tucson, Arizona-based Planetary Science Institute. She and her colleagues spotted the water-shaped features along plains next to the Valles Marineris, a long system of canyons at the Martian equator (photo: a canyon in the Valles Marineris).

"This was a big surprise, because no one thought we'd be seeing these extensive fluvial systems in the plains all around Valles Marineris that were formed during the Hesperian Era," Weitz said in a press release.

"Everyone thought that by then the climate had pretty much dried out."

Weitz and her colleagues describe their findings in the journal Geophysical Research Letters.

Different Animals

Scientists have been curious about the light-toned layered deposits inside Valles Marineris since the Mariner flybys in the early 1970s.

A powerful camera carried by the Mars Reconnaissance Orbiter called HiRISE has now revealed the area in unprecedented detail.

Compared to layered deposits within the Valles Marineris canyons, the layers in adjacent plains vary in color and brightness and reveal different erosion histories, Weitz said.

"Originally, we had thought the layered deposits on the plains might be volcanic rocks produced from explosive eruptions," Weitz told National Geographic News.

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