NASA made a major Mars announcement on Monday, confirming that there is "strong evidence" liquid water flows on the planet.
Here's a look at what we already know about Mars' ability to sustain water and, potentially, life:
The fourth planet from the sun
Orbiting an average of 228.5 million kilometres from the sun, , with much colder temperatures and a thinner atmosphere.
On Monday, NASA Planetary Science Division Director Jim Green described Mars as "the planet that's most like the Earth."
Both Earth and Mars rotate on a similar tilt axis (23.5 degrees for the Earth, 25 degrees for Mars), meaning both planets experience warmer and colder seasons.
But unlike on Earth, where the average temperature is approximately 14 degrees Celsius, Mars records average temperatures closer to minus 62 degrees.
Another difference: the Earth's atmosphere is more than 100 times denser than Mars'.
The recently-discovered water on Mars is liquid and salty
According to NASA's latest findings, salty, liquid water flows intermittently on Mars.
On Monday, the U.S. space agency announced that scientists have detected hydrated minerals on the surface of the planet.
NASA has long hypothesized that dark streaks on Mars' surface, called recurring slope linaea, or RSL, could be caused by water, but the discovery of the hydrated salts appears to confirm this.
"When most people talk about water on Mars, they're usually talking about ancient water or frozen water," Lujendra Ojha, a PhD candidate at the Georgia Institute of Technology, said in a statement on Monday. "Now we know there's more to the story."
Scientists now believe the RSL are caused by underground flowing water that seeps to the surface, causing the dark marks.
"This is a significant development as it appears to confirm that water—albeit briny—is flowing today on the surface of Mars," Grunsfeld said
Mars has a history with water
Three billion years ago, scientists say Mars was a very different planet.
Back then Mars had "an extensive atmosphere," Grunsfeld said on Monday. "And, in fact, it had what we believe was a huge ocean."
, Mars once had a primitive ocean that held more water than Earth's Arctic Ocean.
And while life was first stirring here on Earth, scientists believe it's possible conditions were similarly conducive on the Mars.
"Mars' environment three to three and a half billion years ago was very hospitable," York University Physics and Astronomy Professor Paul Delaney said. "About the same time that life was firing up here on Earth, the Martian environment was quite comparable."
Between then and now, however, Mars underwent massive, unexplained climate change which completely altered its appearance.
Water means life could have existed on Mars in the past - and could still exist in the present
Given the presence of water in both Mars' past and present, scientists say there is a strong chance the planet could support life now, or could have in the past.
Scientists say water is key for supporting life, and evidence suggests Mars is much more humid than once believed.
"Our results may point to more habitable conditions on the surface of Mars than previously thought," study co-author Mary Beth Wilhelm said on Monday.
On Monday, Alfred McEwan, the principal investigator for the HiRISE camera on the Mars Reconnaissance Orbiter, also expressed optimism that life could exist on the planet.
He said the presence of water under Mars' surface means that microbes could already be living in the planet's crust.
"For me, the chances of there being life in the subsurface of Mars is really high," he said.
While Delaney said scientists are confident that macroscopic life does not exist on Mars, it is possible that microscopic life emerged billions of years ago and survived until the present.
"Life has got an amazing amount of tenacity," Delaney said on CTV's Canada AM on Tuesday. "When we look at the variety of life on Earth, including the extremophiles that live in the most bizarre environments, it's not that much of a stretch to think that … microbial life has survived in the warmer, wetter environments beneath (Mars') surface."
Humans could be drinking water on Mars by 2030
Even if alien lifeforms don't exist already on Mars, NASA hopes living, breathing humans will be able to land on the planet in less than 25 years.
According to the NASA Authorization Act of 2010 and the U.S. National Space Policy, the agency is aiming to develop capabilities
As part of that goal, NASA is testing and developing the Orion spacecraft to take humans farther into space than ever before.
Orion on Aug. 26, bringing the program one step closer to human missions.
And, in the event humans do land on Mars, NASA says water on the planet will help them survive.
Although it's salty, astronauts could purify the water for drinking, and even use it to water plants in greenhouses, scientists said on Monday.
