The latest theory devised by astrophysicist revealed that life was brought to Earth by meteorites which transported life from Mars.
Astrophysicists have been exploring the possibility of life developing on two planets within a solar system and any implications for Earth and Mars – our nearest planetary neighbour.
Although Mars is around 130million from the Earth is, scientists believe that billions of years ago it could have been warmer and possibly sustained early forms of microscopic life.
But scientists agree something catastrophic happened that meant it could no longer sustain any life.
NASA recently announced it had worked out that Mars did have an atmosphere that allowed it to hold huge oceans and watercourses on its surface, but this atmosphere was literally stripped away over billions of years by solar winds from the Sun and now only one per cent of that atmosphere remains.
Mr Steffen and his team investigated the process of lithopanspermia – the means by which life-bearing material on one planet can be ejected by meteor impacts and delivered to the surface of another planet.
“Mr Steffen and Gongjie Li, from the Harvard Smithsonian Center for Astrophysics, identified a number of facts that would facilitate the proliferation of life between two planets in a multi-habitable system.”
Mr Steffen said: “Multi-habitable systems could have a microbial family tree with roots and branches simultaneously on two different planets.
“Systems like those that we investigated, and moon systems orbiting a habitable-zone giant planet, are among the few scenarios where life – intelligent life in particular – could exist in two places at the same time and in the same system.”
They believe in our own galaxy, the Milky Way, there may be billions of planetary systems where more than one planet is habitable.
NASA’s Kepler spacecraft has found planet pairs on very similar orbits – with orbital distances differing by as little as 10 percent.
If such a planet pairing occurred in the right place, then both planets could sustain life – and even help each other along.
Mr Steffen said: “It’s pretty intriguing to imagine a system where you have two Earth-like planets orbiting right next to each other.
“If some of these systems we’ve seen with Kepler were scaled up to the size of the Earth’s orbit, then the two planets would only be one-tenth of one astronomical unit apart at their closest approach. That’s only 40 times the distance to the Moon.
“Mars, at best, is 200 times the lunar distance.”
NASA has the Curiosity Rover droid scouring the surface of Mars for evidence of any early life forms, but so far it has drawn a blank, however, it has found the remains of what were once thought to be river delta beds.
The team concluded that the closer two planets were together, the better the chances of a transfer of life.
Firstly, the energy of the meteor impact needed to get material from one planet to another in a multi-habitable system is much less tif they are closer together, so microorganisms are more likely to survive the impact itself.
Secondly, the time needed to traverse the interplanetary distance is much smaller. And thirdly, the way that the impact debris travel through space implies that it is more likely that material from a single impact could hit the destination planet at multiple locations in relatively rapid succession. This scenario would increase the chances of life gaining a foothold.
Despite the challenges that life may have in developing on a planet, it appears that the presence of a nearby companion in the struggle may help.
Mr Steffen added: “At least the climate isn’t likely to be any worse in multi-habitable systems, and the possibility of two planets sharing the biological burden could help the system traverse the inevitable rough times.”