The evidence continues to grow stronger that there's water on Mars, and it flows there today. Water often signals life, so this new discovery gives hope to the search for life in our solar system.

Researchers from the European Space Agency and the Mars Express project announced in February 2019 that they have evidence water once flowed in craters around Mars' northern hemisphere, and — even more shocking — that there is a system of ancient interconnected lakes underground.

The team studied 24 craters that have floors about 4,000 meters below martian "sea level." The floors have features that show water once flowed through them — channels on the crater walls, valleys, deltas and ridged terraces that could all have only been formed by the presence of water. They noted that these findings line up with the previous discovery of a martian ocean that once existed.

"We think that this ocean may have connected to a system of underground lakes that spread across the entire planet," said study co-author Gian Gabriele Ori, director of the Università D’Annunzio’s International Research School of Planetary Sciences, Italy. "These lakes would have existed around 3.5 billion years ago, so may have been contemporaries of a martian ocean."

"Findings like this are hugely important; they help us to identify the regions of Mars that are the most promising for finding signs of past life," said Dmitri Titov, ESA’s Mars Express project scientist.

One potential area that researchers believe may have evidence of life is the southern polar ice cap.

Is there water at the polar ice caps?

Mars closest image NASA/ESA Hubble Space Telescope snapped this portrait of Mars that shows the southern polar ice cap at the bottom. (Photo: NASA/ESA, J. Bell (Cornell U.) and M. Wolff (SSI))

The Italian Space Agency announced in July 2018 the discovery of liquid water underneath the southern polar ice cap. Using the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument (MARSIS) aboard the European Space Agency's Mars Express spacecraft, radar detected a subglacial lake roughly 12.5 miles wide and a mile below the surface.

MARSIS used 29 radar profiles to send radio pulses to measure the planet's surface reflection from May 2012 to December 2015. The pulses detected brightness under the ice caps, and researchers were able to determine the presence of water. They said other theories for the brightness such as a carbon dioxide ice layer above or below the ice cap or a very low temperature water ice aren't possible because they wouldn't cause such a strong reflection as liquid water would.

However, other experts haven't been able to confirm MARSIS' findings.

"We don't see the same reflector with SHARAD [Shallow Radar sounder onboard the Mars Reconnaissance Orbiter], not even when we recently summed together [thousands] of observations to create CATSCAN-like 3-D views of both polar caps," Nathaniel Putzig, Mars Reconnaissance Orbiter SHARAD deputy team leader and senior scientist at the Planetary Science Institute, told CNN. "We're hoping to carry out that same imaging process with the MARSIS data next. I'm excited to see how the 3-D imaging will clarify the view of this detection and whether we will find similar ones elsewhere beneath the polar caps."

Scientists have been trying for years to discover water on Mars

Recurring slope lineae on Mars may've been formed by contemporary flowing water These dark, narrow streaks called recurring slope lineae, which flow downhill on Mars, may have been formed by flowing water. The blue color seen upslope of the dark streaks is not believed to be related to their formation, but instead caused by the presence of the mineral pyroxene. (Photo: NASA/JPL/University of Arizona)

In 2015, NASA revealed evidence of liquid, flowing seasonal water on the Red Planet, which wasn't the same as the recent discovery of the body of water at the southern polar ice cap.

Data from various probes and rovers like Curiosity and the Mars Reconnaissance Orbiter provided researchers with evidence concluding that there is flowing water on present-day Mars. Scientists understand that Mars was once Earth-like with large amounts of water on the surface. Something unknown happened in the planet's history causing it to change. However, this revelation confirms that Mars has harbored water in the past, and that water exists there today. Now, scientists can pursue the implications of what flowing water means in relation to the planet's history and what it could also mean for the potential for life.

Michael Meyer of the Mars Exploration Program at NASA explained, "We found the active process on Mars today that shows that water was a likelihood." He continued with a description of the geological features that caused scientists to suspect water prior to the confirmation of its presence. To show how researchers came to their conclusions, Meyer explained the significance of "recurring slope linea." These RSLs point to the existence of water due to the way they behave. He said, "These are dark streaks that form in late spring, grow in the summer and disappear by fall." In summarizing the data presented during the news conference, Meyer confirmed, "There has been no evidence for water until for now."

Recurring slope lineae emanate out of the walls of Garni crater on MarsRecurring slope lineae emanate out of the walls of Garni crater on Mars. The dark streaks here are up to a few hundred meters in length. The hypothesis is that they are formed by the flow of briny liquid water on Mars. (Photo: NASA/JPL/University of Arizona)

The news was based on research published in Nature Geoscience, which shows how scientists were able to study the RSLs on the planet's surface. Scientists had previously observed these streaks in photos, but because the streaks are only about 5 meters across, researchers could not get a good enough look to determine what was causing them. However, recently scientists found a way to analyze data from the Mars Reconnaissance Orbiter by extracting data from the pictures on a per pixel level. This allows scientists to study smaller details on the Red Planet's surface, and those details provided the new information.

Scientists also have an understanding of the composition of the water. Findings show that hydrated salts are present on the surface of Mars. Hydrated salts would mean that the water on Mars is briny. According to Popular Science, the salt in the water allows it to remain liquid at lower temperatures.

Mary Beth Wilhelm of NASA's Ames Research Center explained that the evidence of water means many things, not the least of which is that microbial life is possible. Also, water on Mars could aid in the human exploration of the planet. Water on Mars would be a crucial resource for astronauts visiting the planet or for long-term colonists. Of course, scientists will need to study the nature of the water to know the full implications.

Researchers have many exciting challenges ahead of them, and one is to determine where the water comes from. Could there be an underground Martian aquifer? Researchers note that there is potential for the Curiosity rover to travel to an RSL and analyze a sample of the liquid. Another possibility is the future Mars 2020 rover or other rovers designed for the task.

The discovery of liquid water on Mars leads to more intriguing questions and mysteries. If there has been life on Mars, where did it come from? How did it survive, what was it like and is it still there? These new findings about liquid water on Mars make scientists and space exploration enthusiasts thirsty for more information.

Editor's note: This article has been updated since it was originally published in September 2015.

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