Scientists have determined that Mars was once a water world like earth.
Around 4 billion years ago, the red planets' molten metal core shut down or exhausted itself. That churning metal core is what powered the magnetic field around Mars and as its core cooled, solar wind and high-energy particles from the sun slowly stripped away Mars' atmosphere. As its atmosphere thinned and the pressure dropped, and all of that Martian water evaporated into space, leaving Mars as the cold, dry desert planet it now is.
Here on Earth, when we look up at the night sky in places free from light pollution from cities, we see the Northern Lights - in essence, a beautiful visual indicator that our planets' metallic core is alive and the magnetic field around us - protecting us - is working.
As Captain Jean Luc Picard from Star Trek TNG often remarked: 'Shields Up'
.gif credit to Universities Space Research Association as well as the Lunar & Planetary Institute
