Rock formed at bottom of ancient body of saltwater, scientists say
http://www.msnbc.msn.com/id/4582649/
By Alan Boyle
Science editor
MSNBC
Updated: 4:07 p.m. ET March 23, 2004
Three weeks after reporting that the Opportunity rover's landing site on Mars was once wet, scientists went even further on Tuesday, declaring that the now-barren rocks were formed at the bottom of an ancient body of saltwater.
The findings, announced at a NASA news briefing in Washington, represent an important link in a chain of evidence hinting that the Red Planet was wet enough and warm enough for a long enough time to support the development of life.
Moreover, if organisms ever did arise, their fossils should still exist within Martian rock, the scientists said.
"If you have an interest in searching for fossils on Mars, this is the first place you want to go," Ed Weiler, NASA's associate administrator for space science, told journalists. He and other space agency officials said the findings could well affect future missions to Mars.
"Opportunity's latest science returns from Mars have profound implications for future exploration," NASA Administrator Sean O'Keefe said.
One step at a time
Members of the rover science team based their conclusions on a microscopic analysis of the bedrock exposed just a few yards (meters) from the spot where Opportunity settled after its landing almost two months ago, at the bottom of a shallow crater in Meridiani Planum.
Three weeks ago, the researchers announced that water once "drenched" the site, based on the presence of sulfate salts and the way crystals within the rock dissolved. But Cornell University's Steven Squyres, the mission's principal scientific investigator, shied away from saying whether the water merely percolated through the subsurface or pooled as bodies of standing water.
As recently as last week, scientists kept mum on the question of groundwater vs. standing water. But after sedimentologists reviewed the microscopic imagery, Squyres and his colleagues decided to take the plunge on Tuesday.
"We think Opportunity is now parked on what was once the shoreline of a salty sea on Mars," Squyres said.
The scientists can't yet say how long ago liquid water covered the area, or for how long, or exactly how deep the water was. NASA said more light could be shed on those questions if Opportunity completes its planned odyssey to the wall of another crater with a thicker exposure of bedrock. The rover emerged from the crater where it landed only Monday and is preparing to drive about a half-mile (700 meters) to the new crater, named Endurance.
Tracing the evidence of ancient water is the primary goal of NASA's $820 million twin-rover mission, which launched Opportunity and Spirit to the Red Planet last summer. Spirit landed on the other side of Mars, in a 90-mile-wide (140-kilometer-wide) crater that scientists suspected was once a lakebed. So far, Spirit has found evidence that a small amount of water made its way to the surface inside molten rock ? but nothing on the scale detected by Opportunity.
Bruce Jakosky, a planetary scientist at the University of Colorado who was not involved in the latest research, said the difference between the earlier findings and the new findings is subtle but important.
"The difference is that this tells us about the climate at the time that the deposits were formed," he told MSNBC.com.
Subsurface water could have been present on a localized basis even if conditions at the surface were barren and dry ? but the evidence for water at the surface itself tells scientists that "conditions must have been conducive to support water in a very widespread way," he said.
Cross-bedding and festooning
The key to the findings reported Tuesday lies in the fine layers within the bedrock. During just one day, Opportunity's microscopic imager snapped 152 pictures of a rock nicknamed "Last Chance" to gather data for analysis. Other pictures were taken of an outcrop called "Upper Dells." All those images were combined to form a wide, up-close mosaic.
In the microscopic view, experts saw unmistakable signs of cross-bedding, in which some of the rock layers lie at angles to the main layers; and festooning, which are smile-shaped curves produced by the shifting of the loose sediments' rippled shapes under a current of water.
"Ripples that formed in wind look different than ripples that formed in water," said science team member John Grotzinger, a sedimentologist at the Massachusetts Institute of Technology. Some of the patterns in the Martian rock could have been created by wind, but others provided reliable evidence of water's role, he said.
Grotzinger determined that the grains of sediment around Opportunity's landing site were shaped into ripples by water at least 2 inches (5 centimeters) deep, and perhaps much deeper. The water would have been flowing at a speed of 4 to 20 inches (10 to 50 centimeters) per second, he said.
The water in which the rock formed need not have been an ocean or even a year-round lake, Grotzinger said. Instead, it could have been a salt flat, or playa, sometimes covered by shallow water and sometimes dry, on the edge of an ocean or in a desert basin. "We're clearly dealing with some kind of transiently wet, transiently dry environment," he said.
Signs of ancient life?
The newly announced findings raise the tantalizing prospect that conclusive traces of fossil organisms could be found within Martian rock.
"The particular type of rock Opportunity is finding, with evaporite sediments from standing water, offers excellent capability for preserving evidence of any biochemical or biological material that may have been in the water," Squyres said. But he emphasized that he was talking about microbial life or perhaps even molecular traces of biology ? evidence that would not be visible to Opportunity's microscopic imager.
Looking for fossil-like features in Martian rock has been a popular pursuit ever since researchers saw "nanofossil" structures in a meteorite from Mars known as ALH84001 in the mid-1990s. Some have even pointed to threadlike or macaroni-shaped features in the Spirit and Opportunity imagery. The earlier controversy over nanofossils has made most mainstream scientists circumspect about using astrobiology's "F-word" ? but if nothing else, Opportunity's findings have whetted NASA's appetite for more.
The two rovers are well into the second half of their 90-day primary mission, but the science team is already laying plans for an extended mission that could last even longer.
Space agency officials are also looking ahead to spacecraft yet to come. Associate Administrator Weiler noted that a more advanced rover, the Mars Science Laboratory, was due for launch in 2009. "Meridiani has now become the prime landing site for that rover," he said. "It will carry astrobiology instruments for the first time."
James Garvin, NASA Headquarters' lead scientist for the moon and Mars, sought to put Opportunity's findings in the larger context of past and future exploration:
"Many features on the surface of Mars that orbiting spacecraft have revealed to us in the past three decades look like signs of liquid water, but we have never before had this definitive class of evidence from the Mars rocks themselves," he said in a prepared statement.
"We planned the Mars Exploration Rover project to look for evidence like this, and it is succeeding better than we had any right to hope. Someday, we must collect these rocks and bring them back to terrestrial laboratories to read their records for clues to the biological potential of Mars."
http://www.msnbc.msn.com/id/4582649/
By Alan Boyle
Science editor
MSNBC
Updated: 4:07 p.m. ET March 23, 2004
Three weeks after reporting that the Opportunity rover's landing site on Mars was once wet, scientists went even further on Tuesday, declaring that the now-barren rocks were formed at the bottom of an ancient body of saltwater.
The findings, announced at a NASA news briefing in Washington, represent an important link in a chain of evidence hinting that the Red Planet was wet enough and warm enough for a long enough time to support the development of life.
Moreover, if organisms ever did arise, their fossils should still exist within Martian rock, the scientists said.
"If you have an interest in searching for fossils on Mars, this is the first place you want to go," Ed Weiler, NASA's associate administrator for space science, told journalists. He and other space agency officials said the findings could well affect future missions to Mars.
"Opportunity's latest science returns from Mars have profound implications for future exploration," NASA Administrator Sean O'Keefe said.
One step at a time
Members of the rover science team based their conclusions on a microscopic analysis of the bedrock exposed just a few yards (meters) from the spot where Opportunity settled after its landing almost two months ago, at the bottom of a shallow crater in Meridiani Planum.
Three weeks ago, the researchers announced that water once "drenched" the site, based on the presence of sulfate salts and the way crystals within the rock dissolved. But Cornell University's Steven Squyres, the mission's principal scientific investigator, shied away from saying whether the water merely percolated through the subsurface or pooled as bodies of standing water.
As recently as last week, scientists kept mum on the question of groundwater vs. standing water. But after sedimentologists reviewed the microscopic imagery, Squyres and his colleagues decided to take the plunge on Tuesday.
"We think Opportunity is now parked on what was once the shoreline of a salty sea on Mars," Squyres said.
The scientists can't yet say how long ago liquid water covered the area, or for how long, or exactly how deep the water was. NASA said more light could be shed on those questions if Opportunity completes its planned odyssey to the wall of another crater with a thicker exposure of bedrock. The rover emerged from the crater where it landed only Monday and is preparing to drive about a half-mile (700 meters) to the new crater, named Endurance.
Tracing the evidence of ancient water is the primary goal of NASA's $820 million twin-rover mission, which launched Opportunity and Spirit to the Red Planet last summer. Spirit landed on the other side of Mars, in a 90-mile-wide (140-kilometer-wide) crater that scientists suspected was once a lakebed. So far, Spirit has found evidence that a small amount of water made its way to the surface inside molten rock ? but nothing on the scale detected by Opportunity.
Bruce Jakosky, a planetary scientist at the University of Colorado who was not involved in the latest research, said the difference between the earlier findings and the new findings is subtle but important.
"The difference is that this tells us about the climate at the time that the deposits were formed," he told MSNBC.com.
Subsurface water could have been present on a localized basis even if conditions at the surface were barren and dry ? but the evidence for water at the surface itself tells scientists that "conditions must have been conducive to support water in a very widespread way," he said.
Cross-bedding and festooning
The key to the findings reported Tuesday lies in the fine layers within the bedrock. During just one day, Opportunity's microscopic imager snapped 152 pictures of a rock nicknamed "Last Chance" to gather data for analysis. Other pictures were taken of an outcrop called "Upper Dells." All those images were combined to form a wide, up-close mosaic.
In the microscopic view, experts saw unmistakable signs of cross-bedding, in which some of the rock layers lie at angles to the main layers; and festooning, which are smile-shaped curves produced by the shifting of the loose sediments' rippled shapes under a current of water.
"Ripples that formed in wind look different than ripples that formed in water," said science team member John Grotzinger, a sedimentologist at the Massachusetts Institute of Technology. Some of the patterns in the Martian rock could have been created by wind, but others provided reliable evidence of water's role, he said.
Grotzinger determined that the grains of sediment around Opportunity's landing site were shaped into ripples by water at least 2 inches (5 centimeters) deep, and perhaps much deeper. The water would have been flowing at a speed of 4 to 20 inches (10 to 50 centimeters) per second, he said.
The water in which the rock formed need not have been an ocean or even a year-round lake, Grotzinger said. Instead, it could have been a salt flat, or playa, sometimes covered by shallow water and sometimes dry, on the edge of an ocean or in a desert basin. "We're clearly dealing with some kind of transiently wet, transiently dry environment," he said.
Signs of ancient life?
The newly announced findings raise the tantalizing prospect that conclusive traces of fossil organisms could be found within Martian rock.
"The particular type of rock Opportunity is finding, with evaporite sediments from standing water, offers excellent capability for preserving evidence of any biochemical or biological material that may have been in the water," Squyres said. But he emphasized that he was talking about microbial life or perhaps even molecular traces of biology ? evidence that would not be visible to Opportunity's microscopic imager.
Looking for fossil-like features in Martian rock has been a popular pursuit ever since researchers saw "nanofossil" structures in a meteorite from Mars known as ALH84001 in the mid-1990s. Some have even pointed to threadlike or macaroni-shaped features in the Spirit and Opportunity imagery. The earlier controversy over nanofossils has made most mainstream scientists circumspect about using astrobiology's "F-word" ? but if nothing else, Opportunity's findings have whetted NASA's appetite for more.
The two rovers are well into the second half of their 90-day primary mission, but the science team is already laying plans for an extended mission that could last even longer.
Space agency officials are also looking ahead to spacecraft yet to come. Associate Administrator Weiler noted that a more advanced rover, the Mars Science Laboratory, was due for launch in 2009. "Meridiani has now become the prime landing site for that rover," he said. "It will carry astrobiology instruments for the first time."
James Garvin, NASA Headquarters' lead scientist for the moon and Mars, sought to put Opportunity's findings in the larger context of past and future exploration:
"Many features on the surface of Mars that orbiting spacecraft have revealed to us in the past three decades look like signs of liquid water, but we have never before had this definitive class of evidence from the Mars rocks themselves," he said in a prepared statement.
"We planned the Mars Exploration Rover project to look for evidence like this, and it is succeeding better than we had any right to hope. Someday, we must collect these rocks and bring them back to terrestrial laboratories to read their records for clues to the biological potential of Mars."
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