It was 2009 when Joseph Levy began poring over images from the surface of the Martian planet. He was fascinated by what he found.
There, in high-resolution photographs beamed back to Earth by the Mars Reconnaissance Orbiter was what Dr Levy describes as the "bullseye".
He was looking deep into the eyes of two craters - known as the Hellas depression and the Galaxias Fossae depression. Others had looked before but nobody saw what he saw.
Last week, Dr Levy and a team of researchers from the University of Texas at Austin, went deep inside the craters for the first time.
They produced detailed 3D measurements to determine with reasonable certainty that if life ever existed on the Red Planet, it existed here.
'IT'S A ROUGH, FRACTURED SURFACE'
Dr Levy, a research associate at the University of Texas Institute of Geophysics, led the project. His findings were this month published in Icarus, the International Journal of Solar System Studies.
He told news.com.au his research points to a "good candidate site for evidence of past life ... provided you could get a rover or an astronaut down into (the craters) safely."
The two sites are well-known. The depressions are both several kilometres across and several hundred metres deep.
For scale, Dr Levy asks that you forgive his Donald Trump reference: "If you put Trump Tower in Chicago at the bottom of the North Hellas depression, only the top 3m would poke out above the plains." Trump Tower is 423m tall.
"It's a rough, fractured surface with lots of ridges and tumbled blocks," he says.
"That roughness is what made the sites initially interesting, but is also makes them difficult to get into."
There's another reason they're interesting to scientists. Despite being formed by different means - an impact event is believed to have formed one crater and volcanic activity the other - they likely host all the ingredients for habitability, including heat, nutrients and water.
Dr Levy explains:
"This project got started when we noticed the first 'bullseye' depressions in the North Hellas site. The Galaxias depression had been known about for several years before, but this is the point where we started thinking that there might be many such cracked depressions on Mars that could tell us about interactions between meteor impacts, volcanic eruptions, and ice.
"The key finding (published this month) is that both depressions appear to be places where large amounts of subsurface ice were removed. The potential combination of heat, meltwater, volcanic gases, and geological weathering products makes these kinds depressions potential habitable zones for past Martian life."
Dr Levy says the Hellas depression lacks the surrounding debris associated with an impact and has a fracture pattern that would indicate ice has melted there. He says the sites are "two of about half a dozen" such structures on Mars.
'LIFE MUST BE LURKING SOMEWHERE'
It's not the first time water was discovered on Mars, but it helps further the idea that conditions exist that are conducive to life. If not in these craters, somewhere.
In September last year, NASA announced the discovery of flowing water. Again, it was the Reconnaissance Orbiter providing the evidence.
Director of planetary science at NASA, Jim Green, said the discovery was "very important".
"Our rover's finding a lot more humidity in the air than we ever imagined. As we inject the soils, they're moist, they're hydrated, full of water," he said at a highly-anticipated press conference.
"These discoveries are very important, but only part of the hydrological cycle on Mars that we are just now beginning to understand. What we are going to announce today is Mars is not the dry, arid planet that we thought of in the past.
"Today, we are going to announce that under certain circumstances, liquid water has been found on Mars."
Dr Levy says the research is a breakthrough for "one of the most fundamental goals of exploration" - finding evidence of past or present life on another world.
"Mars is a great candidate for that search because it has vast areas (much more than Earth) of ancient terrain that formed about the same time that life was beginning to leave evidence of its presence on Earth," he said.
"Finding evidence for past life preserved near the surface would raise the distinct possibility that some organisms could be present deep in the Martian subsurface, similar to the organisms that live deep within Earth's crust.
"As we find more and more habitable locations on Mars - presently habitable, or showing signs of being capable of supporting life in the past - it starts to lead us to the conclusions that life must be lurking somewhere on the planet."
'WE MUST BECOME 'MULTI-PLANET' SPECIES'
Finding life on Mars is one thing. Moving there is another. A number of projects are already under way with the aim of colonising the Red Planet.
There's Mars One, a mission aiming to leave Earth by 2026, and SpaceX, an Elon Musk-led project planning on delivering more than a million people to Mars.
Dr Levy says not only should Earthlings attempts to travel to Mars, they must.
"I think it's imperative for the survival of humans to become a multi-planet species," he told news.com.au.
"I'm not fully convinced that anything short of a major international undertaking or a global strategic conflict on par with the Cold War would provide the motivation needed to get humans to set foot on Mars.
"But I would love to be surprised by start-ups like Mars One or SpaceX. I think human space exploration is one of the most compelling stories imaginable, and would hope that it captures folks' attention and willingness to support exploration.
"If a reality TV series is what it would take to get Mars One off the ground, I imagine folks would tune in. After all, some of the most exciting, heroic-era expeditions to Antarctica were basically funded by the promise of lecture tours, product-placement in photographs, and potential book deals."
Researchers from Brown University and Mouth Holyoke College participated in Dr Levy's study.