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.

"But the association of the deposits with the inverted channels and valleys led us to change our thinking in favor of a fluvial"—i.e. river- or water-associated—"origin for the beds."

Additionally, a spectrometer onboard the Mars Reconnaissance Orbiter identified minerals in the light-toned layered deposits linked to liquid water on Earth.

"Mars Life, Inc."

Andrew Knoll, a Harvard University biologist and member of NASA's Mars program, who was not involved with the new study, called it a welcome paper that "puts another brick in the wall of Mars knowledge."

"Whether it changes the value of stock in Mars Life, Inc., isn't clear," he added.

Weitz also declined to speculate what a longer wet period on the Red Planet might mean for potential life there.

However, the study does appear to extend the window when Mars would have been more hospitable to life.

Prior research by Knoll and other researchers has painted a picture of the Red Planet that, in all but its very earliest years, was too acidic and briny for life as we know it.

More Exploration

Francois Poulet is an astrophysicist at Paris-Sud University in France, who has studied ancient Martian geology.

"There is still an ambiguity in the interpretation of the observed features," he said. "This is very usual in the geology of Mars."

Weitz, the lead study author, agrees that other forces—such as explosive volcanism, wind deposition, and other geological processes—may explain the layered deposits and mineralogy her team identified.

Knoll, the Harvard scientist, noted that many questions remain about the timing and details of geology on early Mars.

"Very early Mars was surely warmer and wetter than the planet has been subsequently, but how warm and how wet remain to be established," he said.

"The Weitz, et al. work fits within this rubbery framework of uncertainty. We've still got lots of exploration to do."

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