If Mars once had running surface water, it also had to have had a substantial atmosphere to prevent the water from simply boiling away into space. So, what happened to Mars' water and air?
Not hard to figure out. Look at the below MOLA results of the MARS surface. MOLA, the Mars Orbital Radar Altimeter spacecraft, took altitude measurements of every inch of the Martian surface.
See that huge, round area, part of the deepest terrain on Mars? That's an impact crater. Sometime in Mars' past, something very big and very nasty hit the planet. If Mars had an atmosphere and oceans when it hit, they were simply blown away into space.
If something the size of the Mars impacter was to hit the Earth, our atmosphere and oceans would suffer the same fate.
Then there would be two planets orbiting the sun that once supported life.
And here we are, all concerned about who the next president may be.
An additional thought:
If the lifeforms on MARS at the time this thing hit could cross space(you know, like intelligent), maybe they saw it coming, had no way to stop it, knew what was going to happen, so they migrated to Earth.
That would make us all illegal aliens.