Jaw-dropping images give us a first glimpse of Mars' liquid water

For years, a team of NASA scientists had pondered over the enigmatic dark streaks lining the inner and outer faces of craters on the Martian surface shown below.

But no longer. NASA announced the answer to the conundrum on Monday: The streaks are evidence of flowing water.

Most mysterious about these streaks - which can be as long as a football field - was that they appeared to change in size over time, growing longer during Mars's warm summer months and shrinking during colder seasons:

If these photos were taken on Earth, the immediate conclusion would be flowing water. But this is Mars - a place where liquid water had never before been discovered.

All that changed on Monday, when the NASA team announced that these dark, mysterious features were, indeed, flowing water.

There are many pieces that had to fit together to finally conclude, beyond a doubt, that this was water and not a bizarre pattern from Martian weather. One of the convincing pieces of evidence was that the streaks flow down hill, as shown here:

And here:

But what ultimately convinced the team that it was water, instead of another form of liquid, was when they used instruments on board NASA's Mars Reconnaissance Orbiter (MRO) - a satellite in orbit around the Red Planet.

MRO has an instrument called a spectrometer, which scans the Martian surface and identifies the chemical make-up of what's down there. From these scans, the team identified hydrated salts within the dark streaks.

The importance of these salts is that they "would lower the freezing point of a liquid brine, just as salt on roads here on Earth causes ice and snow to melt more rapidly," NASA explained in a press release. Here's a false-color image showing just how prevalent these streaks are:

This means that frozen salt water could thaw into a liquid at lower temperatures, which is important since the hottest days on Mars only reach about 70 degrees Fahrenheit.

Whether the streaks themselves are flowing water or simply result of it is still a mystery.

Nevertheless, "the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks," Lujendra Ojha of the Georgia Institute of Technology and lead author on the paper describing the team's findings, said.

The team identified a handful of places on Mars with evidence of these hydrated salts. In the map below, red triangles indicate where rovers have identified hydrated salts in the past. Blue triangles point to where the team found evidence for the salts:

The scientists don't know yet where this water is coming from and how much of it exists.

"Now that we know what we're looking for, we can begin to better search and look and see if there is an aquifer network supplying these, but that is actually the next step," Michael Meyer, the lead scientist for the Mars Exploration Program at NASA Headquarters, said during the media briefing.

Check out the briefing in the video below or on YouTube: