CAPE CANAVERAL, Fla. (AP) — Mars appears to be flowing with rivulets of salty water, at least in the summer, scientists reported Monday in a finding that boosts the odds of life on the red planet.
"It suggests that it would be possible for there to be life today on Mars," NASA's science mission chief, John Grunsfeld, said at a news conference.
Scientists in 2008 confirmed the existence of frozen water on Mars. Now instruments aboard NASA's Mars Reconnaissance Orbiter have yielded the strongest evidence yet that salt water in liquid form trickles down certain Martian slopes each summer, according to the researchers.
"Mars is not the dry, arid planet that we thought of in the past," said Jim Green, director of planetary science for NASA. "Under certain circumstances, liquid water has been found on Mars."
The rivulets — if that's what they are, since the evidence for their existence is indirect — are about 12 to 15 feet wide and 300 feet or more long, scientists said.
"What we're dealing with is wet soil, thin layers of wet soil, not standing water," said Alfred McEwen of the University of Arizona at Tucson, the principal scientist for the Mars Reconnaissance Orbiter's high-resolution imaging experiment.
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Discoveries about Mars, including signs of water
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This Jan. 19, 2016, self-portrait of NASA's Curiosity Mars rover shows the vehicle at "Namib Dune," where the rover's activities included scuffing into the dune with a wheel and scooping samples of sand for laboratory analysis.
(Photo via NASA/JPL-Caltech/MSSS)
This Dec. 18, 2015, view of the downwind face of "Namib Dune" on Mars covers 360 degrees, including a portion of Mount Sharp on the horizon. (Photo via NASA/JPL-Caltech/MSSS)
A photo taken by NASA's Spirit rover near Home Plate shows silica formations poking out of the soil, which may have been formed by microbial life. (NASA/JPL-Caltech)
These dark, narrow, 100 meter-long streaks called recurring slope lineae flowing downhill on Mars are inferred to have been formed by contemporary flowing water. Recently, planetary scientists detected hydrated salts on these slopes at Hale crater, corroborating their original hypothesis that the streaks are indeed formed by liquid water. The blue color seen upslope of the dark streaks are thought not to be related to their formation, but instead are from the presence of the mineral pyroxene. The image is produced by draping an orthorectified (Infrared-Red-Blue/Green(IRB)) false color image (ESP_030570_1440) on a Digital Terrain Model (DTM) of the same site produced by High Resolution Imaging Science Experiment (University of Arizona). Vertical exaggeration is 1.5. (Photo by NASA/JPL/University of Arizona)
Dark narrow streaks called recurring slope lineae emanating out of the walls of Garni crater on Mars. The dark streaks here are up to few hundred meters in length. They are hypothesized to be formed by flow of briny liquid water on Mars. The image is produced by draping an orthorectified (RED) image (ESP_031059_1685) on a Digital Terrain Model (DTM) of the same site produced by High Resolution Imaging Science Experiment (University of Arizona). Vertical exaggeration is 1.5. (Photo by NASA/JPL/University of Arizona)
The dark, narrow streaks flowing downhill on Mars at sites such as this portion of Horowitz Crater are inferred to be formed by seasonal flow of water on modern-day Mars. The streaks are roughly the length of a football field.
The imaging and topographical information in this processed view come from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
These dark features on the slopes are called "recurring slope lineae" or RSL. Planetary scientists using observations with the Compact Reconnaissance Imaging Spectrometer on the same orbiter detected hydrated salts on these slopes at Horowitz Crater, corroborating the hypothesis that the streaks are formed by briny liquid water. (Photo by NASA/JPL-Caltech/Univ. of Arizona)
Recurring slope lineae (RSL) are active flows on warm Martian slopes that might be caused by seeping water. One of the most active sites known on Mars is in the central peaks (uplifted mountains of deep bedrock) of Hale Crater.
This image shows RSL extending downhill from bedrock cliffs, mostly towards the northwest (upper left). This image was acquired in middle summer when RSL are most active in the southern mid latitudes.
The RSL in Hale have an unusually "reddish" color compared to most RSL, perhaps due to oxidized iron compounds, like rust. Since HiRISE color is shifted to infra-red wavelengths, they are actually especially bright the near-infrared just beyond the range of human vision.
This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle above the "Buckskin" rock target, where the mission collected its seventh drilled sample. (Photo via NASA)
The HiRISE camera aboard NASA's Mars Reconnaissance Orbiter acquired this closeup image of a "fresh" (on a geological scale, though quite old on a human scale) impact crater in the Sirenum Fossae region of Mars on March 30, 2015. This impact crater appears relatively recent as it has a sharp rim and well-preserved ejecta. (Photo by NASA)
Seasonal frost commonly forms at middle and high latitudes on Mars, much like winter snow on Earth. However, on Mars most frost is carbon dioxide (dry ice) rather than water ice. This frost appears to cause surface activity, including flows in gullies. (Photo via NASA)
The image shows part of the Arabia Terra region, which is scattered with craters of varying sizes and ages. The craters in this image, caused by impacts in Mars’ past, all show different degrees of erosion. Some still have defined outer rims and clear features within them, while others are much smoother and featureless, almost seeming to run into one another or merge with their surroundings.
This color image was taken by Mars Express’s High Resolution Stereo Camera on 19 November 2014, during orbit 13728. The image resolution is about 20 m per pixel.
(Photo by ESA/DLR/FU Berlin)
Gale Crater, home to NASA's Curiosity Mars rover, shows a new face in this image made using data from the THEMIS camera on NASA's Mars Odyssey orbiter. The colors come from an image processing method that identifies mineral differences in surface materials and displays them in false colors. (Photo via NASA)
The High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA's Mars Reconnaissance Orbiter acquired this closeup image of a light-toned deposit in Aureum Chaos, a 368 kilometer (229 mile) wide area in the eastern part of Valles Marineris, on Jan. 15, 2015, at 2:51 p.m. local Mars time. (Photo via NASA)
This 360-degree panorama from the Navigation Camera (Navcam) on NASA's Curiosity Mars rover shows the surroundings of a site on lower Mount Sharp where the rover spent its 1,000th Martian day, or sol, on Mars, in May 2015. The site is near "Marias Pass." (Photo by NASA/JPL-Caltech)
This Martian scene shows contrasting textures and colors of "Hinners Point," at the northern edge of "Marathon Valley," and swirling reddish zones on the valley floor to the left. (Photo by NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.)
Mars true-color globe showing Terra Meridiani. (Photo by NASA/Greg Shirah)
Among the many discoveries by NASA's Mars Reconnaissance Orbiter since the mission was launched on Aug. 12, 2005, are seasonal flows on some steep slopes. (Photo via NASA)
MOUNT SHARP, MARS - JANUARY 2015: In this handout provided by NASA/JPL-Caltech/MSSS This self-portrait of NASA's Curiosity Mars rover shows the vehicle at the 'Mojave' site, where its drill collected the mission's second taste of Mount Sharp. The scene combines dozens of images taken during January 2015 by the MAHLI camera at the end of the rover's robotic arm. (Photo by NASA/JPL-Caltech/MSSS via Getty Images)
This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp. (Photo via NASA)
MOUNT SHARP, MARS - APRIL 10, 2015: In this handout provided by NASA/JPL-Caltech/MSSS A sweeping panorama combining 33 telephoto images into one Martian vista presents details of several types of terrain visible on Mount Sharp from a location along the route of NASA's Curiosity Mars rover. The component images were taken by the rover's Mast Camera on April 10, 2015. (Photo by NASA/JPL-Caltech/MSSS via Getty Images)
GALE CRATER, MARS - APRIL 10, 2015: In this handout provided by NASA/JPL-Caltech/MSSS, NASA's Curiosity Mars rover recorded this view of the sun setting at the close of the mission's 956th Martian day, or sol April 15, 2015, from the rover's location in Gale Crater, Mars. (Photo by NASA/JPL-Caltech/MSSS/Texas A&M Univ via Getty Images)
Twelve orbits a day provide the Mars Global Surveyor MOC wide angle cameras a global 'snapshot' of weather patterns across the planet. (Photo by: Universal History Archive/UIG via Getty Images)
This 360-degree panorama from the Navigation Camera (Navcam) on NASA's Curiosity Mars rover shows the surroundings of a site on lower Mount Sharp where the rover spent its 1,000th Martian day, or sol, on Mars. (Photo via NASA)
IN SPACE - SEPTEMBER 2: In this handout image provided by NASA/JPL-Caltech/MSSS, and captured by NASA's Curiosity rover, a rock outcrop called Link pops out from a Martian surface that is elsewhere blanketed by reddish-brown dust, showing evidence for an ancient, flowing stream, September 2, 2012. The fractured Link outcrop has blocks of exposed, clean surfaces. Rounded gravel fragments, or clasts, up to a couple inches (few centimeters) in size are in a matrix of white material. Many gravel-sized rocks have eroded out of the outcrop onto the surface, particularly in the left portion of the frame. The outcrop characteristics are consistent with a sedimentary conglomerate, or a rock that was formed by the deposition of water and is composed of many smaller rounded rocks cemented together. Water transport is the only process capable of producing the rounded shape of clasts of this size. (Photo by NASA/JPL-Caltech/MSSS via Getty Images)
IN SPACE - AUGUST 8: In this handout image provided by NASA and released on August 8, 2012, the four main pieces of hardware that arrived on Mars with NASA's Curiosity rover are spotted by NASA's Mars Reconnaissance Orbiter (MRO). The High-Resolution Imaging Science Experiment (HiRISE) camera captured this image about 24 hours after landing. The large, reduced-scale image points out the strewn hardware: the heat shield was the first piece to hit the ground, followed by the back shell attached to the parachute, then the rover itself touched down, and finally, after cables were cut, the sky crane flew away to the northwest and crashed. The relatively dark areas in all four spots are from disturbances of the bright dust on Mars, revealing the darker material below the surface dust. (Photo by NASA/JPL-Caltech/Univ. of Arizona via Getty Images)
IN SPACE - AUGUST 5: In this handout image provided by NASA/JPL-Caltech/MSSS, This color thumbnail image was obtained by NASA's Curiosity rover during its descent to the surface on Aug. 5 PDT and transmitted to Spaceflight Operations Facility for NASA's Mars Science Laboratory Curiosity rover at Jet Propulsion Laboratory (JPL) in Pasadena, California. The image from Curiosity's Mars Descent Imager illustrates the roughly circular swirls of dust kicked up from the Martian surface by the rocket motor exhaust. At this point, Curiosity is about 70 feet (20 meters) above the surface. This dust cloud was generated when the Curiosity rover was being lowered to the surface while the Sky Crane hovered above. This is the first image of the direct effects of rocket motor plumes on Mars and illustrates the mobility of powder-like dust on the Martian surface. It is among the first color images Curiosity sent back from Mars. The original image from MARDI has been geometrically corrected to look flat. The MSL Rover named Curiosity is equipped with a nuclear-powered lab capable of vaporizing rocks and ingesting soil, measuring habitability, and whether Mars ever had an environment able to support small life forms called microbe. (Photo by NASA/JPL-Caltech/MSSS via Getty Images)
A portion of the west rim of Endeavour crater sweeps southward in this false color view from NASA's Mars Exploration Rover Opportunity. (Photo by: Universal History Archive/UIG via Getty Images)
WINDJANA, MARS - APRIL/MAY 2015: In this handout composite provided by NASA/JPL-Caltech/MSSS NASA's Curiosity Mars rover used the camera at the end of its arm in April and May 2014 to take dozens of component images combined into this self-portrait where the rover drilled into a sandstone target called 'Windjana.' The camera is the Mars Hand Lens Imager (MAHLI), which previously recorded portraits of Curiosity at two other important sites during the mission. (Photo by NASA/JPL-Caltech/MSSS via Getty Images)
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Because liquid water is essential to life, the findings could have major implications for the possibility of Martian life. The researchers said in the journal Nature Geoscience that further exploration is warranted to determine whether microscopic life exists on the planet.
McEwen said he, for one, believes the possibility of life on Mars to be "very high," though it would be microbial and somewhere in the Martian crust.
The presence of liquid water could also make life easier for astronauts visiting or living on Mars. Water could be used for drinking and for creating oxygen and rocket fuel. NASA's goal is to send humans there in the 2030s.
The evidence of flowing water consists largely of dark, narrow streaks on the surface that tend to appear and grow during the warmest Martian months and fade the rest of the year.
Mars is extremely cold even in summer, and the streaks are in places where the temperature is as low as minus-10 degrees Fahrenheit. But salt can lower the freezing point of water and melt ice.
The source of the water is a mystery. Scientists noted it could be melting ice, an underground aquifer, water vapor from the thin Martian atmosphere, or some combination.
McEwen said that there appears to be a "significant volume" of water, speculating it could fill many Olympic swimming pools, but that it is spread thin.
The streaks were spotted by the orbiter's high-resolution, telescopic camera. Another on-board instrument detected the chemical signature of salt compounds combined with water.
Michael Meyer, lead scientist for NASA's Mars exploration program, said the only definitive way for now to determine whether there's life on Mars is to collect rocks and soil for analysis on Earth — something a U.S. lander set for liftoff in 2020 will do.
Now that scientists know what they're looking for, a better, more methodical search can be carried out, Green said.
"Water is one of the most precious resources necessary for a human mission to the red planet," said Rep. Lamar Smith, R-Texas, chairman of the House science, space and technology committee. "The more evidence we find of it, the more encouraged I am for future Mars missions."
Present-day Mars is nothing like ancient Mars. Three billion years ago, our most Earthlike neighbor had a huge ocean, but something radical happened, and exactly what remains a mystery.
The idea of water — and life — on Mars has been irresistible to earthlings for generations.
In 1877, Italian astronomer Giovanni Schiaparelli spied what he called "canali" on Mars — Italian for "channels" — but the word was mistranslated as "canals" in English, causing imaginations to run wild. In the early 1900s, amateur astronomer Percival Lowell claimed to have spotted irrigation canals and theorized they were built by Martians.
In 2008, NASA's Phoenix spacecraft landed on Mars and confirmed the long-suspected presence of ice in the soil. The Mars Reconnaissance Orbiter has been circling the planet since 2006.
The lead author of the research paper, Lujendra Ojha, is a Ph.D. candidate at Georgia Institute of Technology.
For NASA, at least, the timing couldn't be better. This Friday, the NASA-approved movie "The Martian" has its premiere.
Related: Watch the trailer for "Citizen Mars," an AOL Originals series following five of the finalists for the Mars One mission. They are everyday people determined to be the first to colonize the Red Planet.