A new finding raises doubts about the 2006 report that the bright spots on Mars some gullies suggest that liquid water flowed down the gullies sometime since 1999.
"It includes pure liquid water," says lead author Jon D. Pelletier of the University of Arizona in Tucson.
Pelletier and his colleagues used topographic data from the images of Mars from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Since 2006, HiRISE was the most detailed pictures ever of Mars from orbit.
The researchers applied basic research in physics, as the fluid flows under the conditions of Mars, as a stream of pure liquid water would look like in the HiRISE images over how an avalanche of dry granular debris such as sand and gravel would be.
"The dry granular case was the winner," says Pelletier, UA associate professor of Geosciences. "I was surprised. I began to think we would prove it is liquid water."
Finding liquid water on the surface of Mars would mean the best seats to current life on Mars, says co-author Alfred S. McEwen, a professor of UA Planetary Sciences.
"What we hope to do was due to the dry-flow model, but that has not happened," said McEwen, HiRISE principal investigator and director of UA's Planetary Image Research Laboratory.
An avalanche of dry debris is a much better match for their calculations and also what their computer model predicts, says Pelletier and McEwen.
Pelletier says: "Right now, the balance of evidence suggests that the dry granular case is the most likely."
They add that their research does not exclude that the pictures show, currents of very thick mud with about 50 percent to 60 percent of the sediment. Such mud would have a consistency similar to molasses or hot lava. From orbit, the resulting deposit would be similar to that of a dry avalanche.
In December 2006, Michael Malin and his colleagues published an article in the journal Science before the bright stripes formed that in two gullies Mars since 1999 "suggest that liquid water flowed on the surface of Mars during the last ten years."
Malin team used images from the Mars Global Surveyor Mars Orbital Camera (MOC) of water troughs, had before 1999. Repeat images of the gullies in 2006 showed bright stripes, which were not there in the earlier pictures.
Then Pelletier and McEwen were at a scientific meeting and began chatting about the amazing new knowledge. They discussed how much more detailed images from HiRISE could be used to meat from the Malin team findings.
Pelletier had experience in dealing with the stereoscopic computer-generated topographic maps known as digital elevation models (DEMs), to find out how special landscape.
DEMs with images of the landscape, from two different angles.
The Mars Reconnaissance Orbiter spacecraft will regularly point on targets so that high-resolution stereo images, says McEwen.
Kirk DM of a crater in the Centauri Montes region, where the Malin team found a new bright stripes in a gully.
Once the DM, Pelletier uses the topographic information together with a commercially available numerical computer model to predict, such as deposits in this particular gully would appear, if a pure water compared to flood, the deposits appear as if they an avalanche dry.
The model also predicts specific conditions necessary to prevent any kind of debris flow.
"This is the first time that someone has applied for numerical computer models to the bright deposits in gullies on Mars or on DEMs produced by HiRISE images," says Pelletier.
When he compared the realities of the deposit and its bright HiRISE image to the predictions from the model, the dry avalanche model was a better fit.
"The dry granular case is simpler and largely complies with the observations," says Pelletier. "It is only a test. It's either more like one or more as b. We were surprised that it is more like B."
Pelletier, says these new findings show, "There are other ways to get deposits that look like these that did not require water."
One of the teams in the next steps with HiRISE images to examine similar bright deposits on less steep slopes to clarify what processes might have formed these deposits.
"It includes pure liquid water," says lead author Jon D. Pelletier of the University of Arizona in Tucson.
Pelletier and his colleagues used topographic data from the images of Mars from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Since 2006, HiRISE was the most detailed pictures ever of Mars from orbit.
The researchers applied basic research in physics, as the fluid flows under the conditions of Mars, as a stream of pure liquid water would look like in the HiRISE images over how an avalanche of dry granular debris such as sand and gravel would be.
"The dry granular case was the winner," says Pelletier, UA associate professor of Geosciences. "I was surprised. I began to think we would prove it is liquid water."
Finding liquid water on the surface of Mars would mean the best seats to current life on Mars, says co-author Alfred S. McEwen, a professor of UA Planetary Sciences.
"What we hope to do was due to the dry-flow model, but that has not happened," said McEwen, HiRISE principal investigator and director of UA's Planetary Image Research Laboratory.
An avalanche of dry debris is a much better match for their calculations and also what their computer model predicts, says Pelletier and McEwen.
Pelletier says: "Right now, the balance of evidence suggests that the dry granular case is the most likely."
They add that their research does not exclude that the pictures show, currents of very thick mud with about 50 percent to 60 percent of the sediment. Such mud would have a consistency similar to molasses or hot lava. From orbit, the resulting deposit would be similar to that of a dry avalanche.
In December 2006, Michael Malin and his colleagues published an article in the journal Science before the bright stripes formed that in two gullies Mars since 1999 "suggest that liquid water flowed on the surface of Mars during the last ten years."
Malin team used images from the Mars Global Surveyor Mars Orbital Camera (MOC) of water troughs, had before 1999. Repeat images of the gullies in 2006 showed bright stripes, which were not there in the earlier pictures.
Then Pelletier and McEwen were at a scientific meeting and began chatting about the amazing new knowledge. They discussed how much more detailed images from HiRISE could be used to meat from the Malin team findings.
Pelletier had experience in dealing with the stereoscopic computer-generated topographic maps known as digital elevation models (DEMs), to find out how special landscape.
DEMs with images of the landscape, from two different angles.
The Mars Reconnaissance Orbiter spacecraft will regularly point on targets so that high-resolution stereo images, says McEwen.
Kirk DM of a crater in the Centauri Montes region, where the Malin team found a new bright stripes in a gully.
Once the DM, Pelletier uses the topographic information together with a commercially available numerical computer model to predict, such as deposits in this particular gully would appear, if a pure water compared to flood, the deposits appear as if they an avalanche dry.
The model also predicts specific conditions necessary to prevent any kind of debris flow.
"This is the first time that someone has applied for numerical computer models to the bright deposits in gullies on Mars or on DEMs produced by HiRISE images," says Pelletier.
When he compared the realities of the deposit and its bright HiRISE image to the predictions from the model, the dry avalanche model was a better fit.
"The dry granular case is simpler and largely complies with the observations," says Pelletier. "It is only a test. It's either more like one or more as b. We were surprised that it is more like B."
Pelletier, says these new findings show, "There are other ways to get deposits that look like these that did not require water."
One of the teams in the next steps with HiRISE images to examine similar bright deposits on less steep slopes to clarify what processes might have formed these deposits.
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