By: SPACE.com Staff
Published: 10/24/2012 12:16 PM EDT on SPACE.com
The tantalizing seasonal flows observed on Mars last year may indeed be caused by liquid water, a new study suggests.
The melting and subsequent evaporation of frozen salty water could cause the intriguing dark streaks, researchers said. These lines, which were spotted by NASA's Mars Reconnaissance Orbiter spacecraft, extend down some Martian slopes during warm months and fade when winter comes.
“In one day we could form enough liquid to create these flow features on the surface," lead author Vincent Chevrier, of the University of Arkansas, said in a statement.
Chevrier and co-author Edgard Rivera-Valentin, now at Brown University, modeled the behavior of water-and-salt mixtures called brines. Salts can lower the melting point of water, explaining how brines could conceivably flow on Mars' frigid surface.
The researchers plugged different forms of salt into their model, attempting to find one that exhibits the desired behavior.
"We had to find a salt-water mixture that would come and go," Chevrier said.
They determined that calcium chloride fits the bill. In their models, the researchers could melt enough calcium chloride brine that it would not all evaporate immediately, leaving some liquid behind to conceivably create the flow features.
The researchers say their model fits the observed phenomenon well. For example, it explains why the streaks — known as Recurring Slope Lineae — occur seasonally on equator-facing slopes, and why imaging spectrometry on Mars hasn't identified water signatures in such places (because the liquid would evaporate quite quickly).
"No other current model really explains all the observations," Chevrier said.
Evidence abounds that water once flowed across many parts of Mars billions of years ago. NASA's Spirit and Opportunity rovers found many signs at their disparate landing sites after touching down in 2004, for example, and the agency's Mars rover Curiosity rolled past an ancient streambed just a month or so ago.
Scientists have long viewed the modern-day Red Planet as a dry and dusty place, however, which is why the discovery of the seasonal flow features last year created such a stir.
Here on Earth, life teems wherever liquid water is found. So if Mars is wet today — even if only seasonally — the planet may be a better candidate to host life than scientists had thought.
The new study will be published in an upcoming issue of the journal Geophysical Research Letters.
- Photos: The Search for Water on Mars
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Viking 1 launches from NASA's Kennedy Space Center on August 20, 1975, bound for Mars. A twin spacecraft, Viking 2, followed about three weeks later.
Each Viking spacecraft had two parts--an orbiter (top left) and lander (bottom left). After orbiting Mars and scouting for landing sites, the orbiter and lander would separate. Then the lander, protected from intense hear by an "aeroshell," would parachute to a safe landing (right).
In Mars Orbit
This image from June 29, 1976, shows a 30 mile wide swath of Chryse Planitia dominated by Belz Crater. It's known as a "rampant crater" because of the raised ridge around the inner layer of ejecta, material thrown out from a volcano or meteor impact.
Viking 1 touched down on July 20, 1976, seven years to the day after the first moon landing. Just minutes later, the lander took this photograph, the first picture ever taken in the surface of Mars.
Stars And Stripes
At left, the American flag is seen on the Viking 1 lander with the bicentennial symbol and Viking symbol below. At right, the six foot long rock known as "Big Joe" looms about 25 feet from the lander.
First Color Image
This is the first color image of the surface of Mars, snapped by Viking 1 the day after landing. The rocky wasteland, covered by iron oxide, at last provided an image to match the nickname "red planet."
In The Trenches
Viking 1's sampling arm created a number of deep trenches in the red planet's soil as part of surface composition and biology experiments.
Meanwhile, the Viking 1 Orbiter continued to snap intriguing photos of the surface, like this photo from the Cydonia region that showed what many thought looked like a human face.
The View From Orbit
A Viking 1 Orbiter image from September 1976 shows debris flows east of the Hellas region. The image is about 174 miles across and the debris flows extend up to 12 miles from the source.
A global mosaic from 102 Viking 1 Orbiter images from February 1980 shows a full Martian hemisphere. The view represents what you would see from a spacecraft about 1500 miles high.
A color mosaic from Viking 1's Orbiter shows the eastern Tharsis region. At left, from top to bottom, are the three 15 mile high volcanic shields, Ascraeus Mons, Pavonis Mons, and Arsia Mons.
A color mosaic from Viking 1 shows the massive Olympus Mons volcano. The largest volcano in the solar system, Olympus Mons is about the same size (in area) as the state of Arizona, nearly 375 miles in diameter and 16 miles high. A crater 50 miles wide sits atop the summit.
A color mosaic from both Viking Orbiters shows a part of Valles Marineris known as Chandor Chasma. The walls and floor show evidence of erosion. The Viking 2 Lander ended communications on April 11, 1980, and the Viking 1 Lander on November 13, 1982, after transmitting over 1400 images of the two sites. The Viking 2 Orbiter was powered down on July 25, 1978 after 706 orbits, and the Viking 1 Orbiter was powered down on August 17, 1980, after over 1400 orbits.