Scientists say high resolution images from the Mars Reconnaissance Orbiter suggest that liquid water is flowing on the surface of Mars.
"We have been looking for liquid water on Mars for a very long time," said Sue Smrekar.
Smrekar works on the Mars Reconnaissance Program at NASA's Jet Propulsion Laboratory in Pasadena.
"Because of the particular time of year on Mars where it formed, we think it has to be water," said Smrekar. "That's the most likely hypothesis."
Scientists have long known that ice exists on Mars, but for the past several years researchers have been focusing on the steep slopes that circle a handful of craters near the planet's equator.
Time lapse images were taken months apart. The dark, finger-like features show up during the warmest months of the year, and then disappear in the winter. Just like spring runoff on Earth.
"As far as liquid water today in places where it is warm enough to stay liquid for awhile, I think that this is the best evidence we have," said Geophysicist Phil Christensen.
At a news conference in Washington on Thursday, researchers said the discovery has huge implications because where there is water, there is life.
"We have no proof of life," said Smrekar. "We have no way to prove that there is life. But it says we have an environment where it is possible."
NASA's new Mars rover, "Curiosity," will be launched in November, but unfortunately it won't get to go anywhere near the crater where this latest discovery was made.
"Curiosity has not been fully sterilized," said Michael Meyer from the Mars Exploration Program. "It wouldn't be allowed to go there for fear of actually contaminating the planet with Earth life."
Scientists say they haven't been able to identify a source for the water. And further tests will be needed to determine if it really is water, or if it's something else, such as mineral deposits or maybe even dust.