A comet bombardment that occurred on Mars 3.9 billion years ago may have created habitable conditions.
It may be a cold and barren world today, but in its distant past scientists believe that Mars was decidedly more Earth-like with its own rivers, oceans and lakes of warm liquid water.
More recently researchers have been focusing on one particular period in the planet’s history – that of the Late Heavy Bombardment – a time during which Mars was being relentlessly pummelled by large comets and asteroids.
Despite its seemingly destructive nature, these impacts may have ultimately benefited conditions on Mars by melting the subsurface ice and producing hydrothermal systems which would have been similar to those that we see in Yellowstone National Park here on Earth.
A large enough impact during this time period could have even kick-started the planet’s water cycle, creating conditions that would have been far more favorable to life than they are on Mars today.
– See more at: http://www.unexplained-mysteries.com/news/292979/did-comets-form-a-haven-for-life-on-mars#sthash.D7FSVcNP.dpuf