NASA now has new clues the Red Planet could have supported life - microbial life, that is.
This is Gale Crater. It was formed some 3.5 billion years ago when a meteor crashed into the surface of Mars.
In the center of the otherwise barren crater is a formation that, until now, had stumped scientists - a 3.5 mile high mountain known as Mount Sharp.
After studying two-and-a-half years of data collected by NASA's Curiosity rover, scientists have found layers of bedrock that looked a lot like those found at the type of river deltas you'd find on Earth.
NASA believes these hundreds of rock layers alternate between lake, river and wind deposits. These sediment deposits accumulated over tens of millions of years to form Mount Sharp.
Curiosity rover finds new signs of a lake on Mars
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)
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)
Mars true-color globe showing Terra Meridiani. (Photo by NASA/Greg Shirah)
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)
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)
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)
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)
This image illustrates possible ways methane might be added to Mars' atmosphere (sources) and removed from the atmosphere (sinks). NASA's Curiosity Mars rover has detected fluctuations in methane concentration in the atmosphere, implying both types of activity occur on modern Mars. A longer caption discusses which are sources and which are sinks.(Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan)
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This is huge because it calls into question the widely-held idea that wet conditions only existed underground on Mars.
In other words, if the climate allowed for a lake, it's possible rain or even an ocean could have existed on Martian soil.
Or as one NASA scientist put it: "Knowledge we're gaining about Mars' environmental evolution by deciphering how Mount Sharp formed will also help guide plans for future missions to seek signs of Martian life."
The data collected by Curiosity is part of NASA's ongoing preparation for a human trip to Mars in the 2030s.