The red planet was probably once white.
New research published today says Mars, like Earth, has just come out of an ice age.
But unlike here -- where the ice caps are shrinking -- on Mars they actually get larger between ice ages.
NASA illustration of how Mars may have once looked (NASA)
Earth's tilt, which causes our seasons, is fairly stable at 23.5 degrees. Mars on the other hand doesn't have a large moon to keep it steady so it wobbles greatly, pulled around by Jupiter.
This means its poles swing between angles of 10 and 40 degrees. When the poles are pointed at the sun, the ice melts redistributes toward the equator, causing an ice age. When the equator is closer to the sun, ice collects at the poles -- which is what is happening now.
"Because the climate on Mars fluctuates with larger swings in axial tilt, and ice will distribute differently for each swing, Mars would look substantially different in the past than it does now," says Dr Isaac Smith, researcher at the Southwest Research Institute in Texas.
The current Mars ice age ended about 370,000 years ago, during the reign of Homo Erectus and the Neanderthals. The poles currently house about 87,000 cubic kilometres of ice, enough to cover the entire planet in ice 60cm deep.
NASA's Mars Reconnaissance Orbiter snapped photos of the poles, showing spiral patterns that helped scientists figure out what was going on.
"At some point we're going to have some people there and we’d like to know where the water is. So there’s a big search for that," says Dr Smith.
It's proof that even though we might not find life as we know it on our closest interplanetary neighbour, Mars is far from a dead world.