Department of Inexistent Carbonates

sfgate.com, August 21, 2003

Paul Recer, AP Science Writer (08-21) 22:51 PDT WASHINGTON (AP) --

Researchers say there is virtually no evidence of limestone formation on Mars, a finding that suggests the Red Planet never had oceans or seas. That conclusion, however, does not alter the possibility of life on Mars, experts say.

Philip Christensen of Arizona State University said that an instrument on NASA's Mars Global Surveyor that searched the entire planet for evidence of carbonate found only trace amounts of the limestone-like mineral.

The finding means it is unlikely that Mars ever had oceans of water as some scientists have suggested, he said.

The finding means it is unlikely that Mars ever had oceans of water as some scientists have suggested, he said.

"Maybe instead of calling them oceans, we should call them glaciers," said Christensen. "A frozen ocean will not form carbonate. I believe Mars has a lot of water, but it is cold and frozen most of the time. That is consistent with what we have seen."

Other Mars experts said the finding makes a significant contribution to the continuing debate among scientists about how much water there was on Mars, where did it go and how did the planet's intricate patterns of river beds, carved canyons and delta fans form without huge volumes of flowing water.

"This is dramatically important," Matt Golombek, a geologist with the Jet Propulsion Laboratory, the lead agency in NASA's program of Mars exploration, said of the new study.

He said there is clear evidence that water flowed on Mars in the past, but yet the thin atmosphere and frigid temperatures of the planet now make liquid surface water impossible. This suggests that Mars was once warmer and wetter and with a denser carbon dioxide atmosphere. The new finding by the Arizona State researchers shows that may not have been the case, said Golombek.

"If you had a warmer, wetter, thicker atmosphere, you would expect to find carbonate somewhere and so far we haven't found it," he said. "This geochemical information is in direct contradiction to an early warmer, wetter Mars."

In the study, Christensen and his co-authors, Joshua L. Bandfield and T. D. Glotch, used a Global Surveyor spacecraft instrument called the thermal emission spectrometer, or TES, that was designed to search for evidence of carbonate minerals on Mars.

Carbonate is formed in the presence of water and carbon dioxide. On Earth, the mineral is found in the immense deposits of limestone that are present on every continent, in soils and layers of stone formed beneath some lakes, seas and oceans.

Mars' atmosphere is mostly carbon dioxide, so it has long been believed that if the planet at one time had large bodies of water then there would have been large deposits of carbonate. But the TES found only trace amounts of the chemical.

Christensen said that even though there may not have been large bodies of liquid water on Mars, some life forms could still have evolved there.

"When people say there are no oceans or lakes, does that mean there was no life? Not at all," he said. "There's the possibility that ice and snow on Mars melted from time to time, forming those gullies and then refreezing again."

Areas where this happened on Mars, he said, "are excellent potential abodes for life and certainly worth looking at."

Golombek agreed, noting that around the edges of large deposits of ice there are small areas of liquid water that could host life.

"On Earth, there are growing communities of microbes that live at the edge of glaciers where you get flashes of water, even though the dominant feature is ice," he said.

Ross Irwin, a geologist with the Smithsonian Institution, said the new finding does not eliminate the possibility that conditions on Mars once allowed for large bodies of standing water on the Red Planet.

He said geological features on Mars, such as basins and river beds, were clearly carved by running water and that it is possible any carbonate formed was carried beneath the surface of the planet, beyond the detection range of the TES.

"Lots of basins have been resurfaced on Mars," said Irwin. "Carbonate could be in the subsurface or buried beneath sediment. There could be extensive carbonate deposits that are difficult to locate."

And:

sfgate.com August 22, 2003

Kenneth Chang, New York Times August 22, 2003

There are no white cliffs of Mars, scientists are reporting, casting more doubt on the theory that Mars once had a warm, wet, Earthlike climate favorable for life.

NASA's Mars Global Surveyor spacecraft, in orbit around the fourth planet, has been measuring the glow of infrared light from the rocks below, looking for patterns of colors that identify different minerals. In particular, scientists have been interested in minerals known as carbonates, which form only in the presence of water. On Earth, the white cliffs of Dover in England are a notable example of carbonates.

In today's issue of the journal Science, the researchers who run the infrared instrument report that Global Surveyor has detected small concentrations of carbonates in Martian dust, 2 to 5 percent by weight, but none of the large deposits that would probably form at the bottom of a lake or an ocean.

"I would say it's extremely unlikely Mars had large bodies of warm, standing water that were exposed to the atmosphere for a long period of time," said Philip R. Christensen, a professor of geological sciences at Arizona State University and senior author of the article. "It's reasonably unlikely that massive carbonates exist and we haven't seen them."

Many planetary geologists are now moving toward the view that Mars has been cold throughout its 4.5 billion-year history and that the considerable quantities of ice known to exist there have been in a frozen state almost all of that time.

"There is a significant shift that has been going on in the last year or two," said Michael H. Carr of the United States Geological Survey in Menlo Park. "I find it easy to believe early Mars was cold, and it never got much above freezing. There are a lot of reasons for thinking that."

In this view, the early environment on Mars, when it did possess a significant atmosphere, may have resembled Antarctica's. However, if Mars has always been freezing cold, that leaves scientists having to explain how a vast network of what appear to be gullies, dry riverbeds and canyons formed on the Martian surface.

Those water-worn features had led some to speculate that Mars long ago had a thick atmosphere of carbon dioxide that trapped enough heat to create balmy conditions. Some even saw geological features that they interpreted as shorelines of an ancient ocean that had covered much of Mars' northern hemisphere.

Since then, scientists have found that realistic climate models do not generate that much global warming on Mars, and high-resolution photographs by Mars Global Surveyor have failed to convince most people that the supposed shorelines are actually shorelines.

Instead of long-lived oceans, lakes and rivers, many scientists are exploring whether the landscape was shaped by temporary wet periods, like torrential boiling downpours after a meteor impact or the movement of water underground.

Victor R. Baker, head of the hydrology and water resources department at the University of Arizona, believes that periodic eruptions of Mars' volcanoes could have altered the climate enough that water could have existed for hundreds to thousands of years, at least in some places.

The new Global Surveyor data, Baker said, only "argues against an Earthlike ocean. Mars clearly had periods of ponded water of great extent on the surface. "

Because of the lack of plate tectonics on Mars, he believes carbonates seeped miles underground, out of view.

Even the low concentrations of carbonates detected could explain where Mars' air, now very thin, has gone. If the top mile or two of Mars' crust also contains 2 to 5 percent carbonates, it would suggest that Mars once had an atmosphere at least as dense as Earth's and possibly three times as dense.

"What we're detecting here is part of Mars' earlier atmosphere," said Dr. Joshua L. Bandfield, another author of the Science article.

Even if Mars was never tropical, it does not mean that the parade of spacecraft headed there over the next decade will have nothing to discover.

"I think glaciers and snow and ice are every bit as interesting and potentially as important for the search for life as oceans," Christensen said. "All we're saying is Mars didn't have warm oceans."