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SALTY METEORITE INDICATES MARS HAD EARTH-LIKE OCEANS
Thanks to NASA's unmanned planetary exploration program, evidence of
the existence of past oceans on Mars has been accumulating for years,
but no one had ever been able to say what the overall chemical
composition of those oceans might actually have been like -- until
now.
College of Liberal Arts and Sciences
Arizona State University
Tempe, Arizona
June 22, 2000
A recent analysis of the interior of a 1.2 billion-year-old Martian meteorite known as the Nakhla Meteorite has shown the presence of water-soluble ions that are thought to have been deposited in cracks by evaporating brine, according to a study by Arizona State University Regents Professor of Chemistry and Geology Carleton Moore, Douglas Sawyer of Scottsdale Community College, ASU graduate student Michael McGehee and Julie Canepa of Los Alamos National Laboratory. The finding, announced in the July issue of the journal Meteoritics and Planetary Science, indicates that ancient Martian oceans had a chemical composition similar in variety and concentration to Earth oceans.
"We have concluded that we have extracted salts that were originally present in Martian water," said Moore. "The salts we found mimic the salts in Earth's ocean fairly closely."
Moore, who is the director of the ASU Meteorite Center, decided to examine the ion content of Martian meteorites in ASU's sizable meteorite collection, when he noticed an oddity in chemical analyses done by Canepa, then a graduate student at ASU, 15 years ago.
"She studied chlorine and sulfur in basalts from all over the solar system, including the moon, the Earth, and the meteorites. At the time, we didn't realize that some of the meteorite basalts came from Mars. Then one day I realized that some of the meteorites were high in chlorine and some were low in chlorine. When I checked on it, it turned out that all the high chlorine meteorites were Martian meteorites and the low chlorine meteorites were all asteroidal."
Then the now-famous study of Martian meteorite ALH48001 helped Moore make a second connection: "When the study of this meteorite revealed not just possible evidence of life but also the presence of salts, I said to myself 'Aha! Perhaps our meteorites' chlorine is the remains of salt that had gotten into the meteorites.' If this was so, it would most likely be from salt water that had leaked in through cracks in the Martian rock the meteorites came from."
Moore chose the Nakhla meteorite to test, since it had the highest chlorine content of all those in the survey. Nakhla is named for El-Nakhla in northern Egypt, where it was found following a meteorite shower in 1911.
"We had a very nice piece of the Nakhla meteorite, about the size of a golf ball so that there was a clean, uncontaminated interior for us to study," Moore said. Sawyer and McGehee prepared the meteorite and carefully drilled into its interior so to get a convincingly uncontaminated sample.
Using an ion chromatograph first on the sample and then on water to which the sample was exposed later, Moore tested for chlorine in both. The results showed that a high percentage of the element present was water soluble and therefore had probably originated from a water solution -- from salt water.
"Then we tested for the other elements and we found the highest concentrations of negative ions were chloride, sulfate, fluoride, and a little dissolved silica , and, in positive ions, sodium, magnesium and calcium," Moore said.
"The elements in highest abundance were sodium and chloride -- like the salt water on Earth. In ocean water, these are the predominant ionic elements. We are interpreting the elements that we have extracted as having come from an early Martian ocean."
The only significant difference Moore found between the ionic elements found in the Martian rock and those found in Earth ocean water was the abundance of calcium, which was significantly higher in the Nakhla meteorite than in sea water. Moore points out, however, that the lower calcium concentration in seawater may be due to the mineral being removed biologically by plants, corals and shellfish. When the Nakhla meteorite left Mars 1.2 billion years ago, life on Earth had not yet evolved to these higher forms (shells only appear in the fossil record about 600 million years ago).
To Moore, the finding is interesting because it implies not just a chemical similarity between the planets that may improve the likelihood of finding life on Mars, but also because it provides a window of sorts into the Earth's own past.
"There was apparently a uniformity between the planets. The inference that the early Martian ocean was very similar to our current ocean also implies that the early Earth's ocean may have been very similar to what it is today. This is a clue to what it might have been."
Photos available at: http://clasdean.la.asu.edu/news/images/marsocean/
Brown University
December 9, 1999
PROVIDENCE, R.I. -- In an article to be published in Science magazine Dec. 10, 1999, Brown University planetary geologist James Head and five colleagues present topographical measurements which they say are consistent with an ocean that dried up hundreds of millions of years ago. The measurements were taken by the Mars Orbiter Laser Altimeter, an instrument aboard the unmanned spacecraft Mars Global Surveyor which is circling the planet.
Head's team set out to test the hypotheses of scientists who suggested the possibility of oceans on Mars in 1989 and 1991. The team used data from the Mars Orbiter Laser Altimeter, which beamed a pulsing laser to Mars' surface. Scientists measured the time it took for the laser to return to the satellite; the laser traveled a shorter length of time from mountain peaks and longer from craters. MOLA is the first instrument to provide scientists the information required to construct a topographic map of the entire surface of the planet.
For years, scientists have known about channels in which water once flowed into the northern lowlands on the surface of Mars. "The question is whether it collected in large standing bodies," Head said. "This is the first time we could get instruments to comprehensively test these ideas."
According to Head, the team has found four types of quantitative evidence that points to the possible ancient ocean:
The results "should make all of us think more seriously about the possibility of the presence of large-scale standing bodies of water on Mars, big lakes and oceans," Head said. "We can't think of anything else to explain these things. They merit much closer scrutiny."
Head's team concludes that further tests are necessary, including analysis of meteorites from Mars and of landing sites, checking for the presence of salts that may be related to former oceans.
The importance of determining whether there were ancient oceans -- and life -- on Mars is that scientists may be able to learn more about long-term climate change and why climate changed on Mars, which has relevance to the future of the Earth, Head said.
Color images are available through the News Service.
IMAGE CAPTIONS:
Possible configuration of ancient oceans on Mars: Topographic portrayal of the surface of Mars derived from Mars Orbiter Laser Altimeter (MOLA) data.
In the images below, areas of high elevation are white, intermediate elevations are brown, and lower elevations are green. The blue areas represent the region that would have been occupied by an ocean earlier in martian history, according to the hypothesis of Parker and co-workers. Recent data from the Mars Global Surveyor Mission MOLA experiment show that the ancient shoreline proposed by Parker and colleagues (located at the edge of the blue area) lies close to the flat line expected if it were indeed an ancient shoreline. The surface below this line is also smoother at all scales than above, consistent with sedimentation from an ancient ocean smoothing topography below sea level.
[Image 1]
In this topographic portrayal of Mars, above, the northern lowlands are
occupied by an ocean (blue) whose shoreline is placed at the position of
Contact 2, the line that Parker and co-workers interpreted as an ancient
shoreline. Thus, this view shows Mars as it might have looked mid-way
through its history according to the oceans hypothesis. The Tharsis region,
with numerous very large shield volcanoes is seen in the central part
of the globe. In the upper right, many channels flow into the northern
lowlands at Chryse Planitia.
Credit: NASA Mars Global Surveyor Project; MOLA Team. Rendering by Peter Neivert, Brown University.
[Image 2]
In this topographic portrayal of Mars, above, giant channels emerge from
the Tharsis region (left), Valles Marineris (bottom), and the ancient heavily
cratered terrain (right), and flow down slope into the northern lowlands
in Chryse Planitia (center). The ancient shoreline proposed by Parker and
co-workers is at the position where the channels change from heavy
scouring of the background terrain into smooth terrain typical of the
northern lowlands, suggesting that they once flowed into a standing body
of water, or ocean, as portrayed in the blue area here.
Credit: NASA Mars Global Surveyor Project; MOLA Team. Rendering by Peter Neivert, Brown University.
NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA
Malin Space Science Systems, San Diego, CA
Oct 1, 1999
One argument that such a body of water once existed was suggested by features in images from the NASA Viking missions taken in the 1970s, which were interpreted by a number of researchers as remnants of ancient coastlines. The images from Mars Global Surveyor, taken in 1998, have a resolution five to 10 times better than those that Viking provided. With this closer inspection, none of these features appears to have been formed by the action of water in a coastal environment.
"The ocean hypothesis is very important because the existence of large bodies of liquid water in the Martian past would have had a tremendous impact on ancient Martian climate and implications for the search for evidence of past life on the planet," said Dr. Kenneth Edgett, a staff scientist at Malin Space Science Systems (MSSS), San Diego, CA, the institution that built and manages the Mars Orbiter Camera onboard the spacecraft. "The newer images do not show any coastal landforms in areas where previous researchers --working with lower resolution Viking images -- proposed there were shorelines."
About 2 percent of the Mars Orbiter Camera images were targeted to look in places that would test shorelines proposed by others in the scientific literature.
"Even on Earth, looking for ancient shorelines from the air or space is a challenge," said Dr. Michael Malin, principal investigator for the camera at MSSS. "Despite these difficulties, we believe these Mars Orbiter Camera images of the proposed shorelines are of a high-enough resolution that they would have shown features indicative of a coastal environment had there been an ancient ocean on Mars."
The paper containing these new conclusions will be published in the Oct. 1 issue of the Journal of Geophysical Research Letters.
One area that might have been a coastline is located northwest of the great volcano Olympus Mons. Researchers looking at Viking images have suggested that there might be a cliff separating the western margin of the Lycus Sulci uplands from the lower-elevation, smoother Amazonis plains. The proposed cliff looked like the kind that forms on Earth from erosion as waves break against a coastline.
Three high-resolution images were taken of this proposed coastline. The uplands are roughly textured, while the flat plains appear smoother. The image shows that the contact between the two regions is clearly not a wave-cut cliff, nor are there any features that can be unambiguously identified as coastal landforms, according to Malin.
"While the suggestion that Mars at one time had oceans cannot be ruled out, the foundation for the 'ocean hypothesis' developed in the 1980s on the basis of suspected shorelines appears now to have been incorrect," Malin concluded. "However, it should be understood that there is significant other evidence of water on Mars in the past, both from Mars Global Surveyor and from previous missions. Today, the Mars Orbiter Camera continues to acquire new high-resolution pictures, each one helping to search for clues to the very important question of the role of water in the evolution of Mars."
More information and images about the Mars Global Surveyor mission is available at:
http://mars.jpl.nasa.gov/mgs/
and
http://photojournal.jpl.nasa.gov
Additional details about the paper and the new Mars images are at:
http://www.msss.com/mars_images/moc/grl_99_shorelines/
Mars Global Surveyor is the first in a long-term program of Mars exploration, known as the Mars Surveyor Program that is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology, Pasadena, CA.
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