Life on 'habitable' exoplanet probably couldn't spread
Any life on the 'super-Earth' Gliese 581-d is unlikely to make it off the planet and onto others within its solar system.
While conditions there are believed to be suitable for life, living microbes wouldn't be able to spread as easily as within our own solar system.
"One of the big scientific questions is how did life get started and how did it spread through the universe," says Jay Melosh of Purdue University.
"That question used to be limited to just the Earth, but we now know in our solar system there is a lot of exchange that takes place, and it's quite possible life started on Mars and came to Earth. There's also been a great deal of discussion about the possible spread of life in the universe from star to star."
Student Laci Brock examined the Gliese 581 planetary system and found that it would be very difficult for materials such as meteorites to spread.
All four planets in the system are very close to the central star, giving them high orbital velocities. However, the initial velocity of material leaving Planet d simply isn't enough to allow exchanges among planets.
"Ejections from Planet d have a low probability of impact on any other planet than itself, and most ejected particles would enter an initial hyperbolic orbit and be ejected from the planetary system," says Brock.
It appears that a more extended solar system would be needed for exchange of materials among planets - and none yet discovered fits the bill.
"Planet d would have a very small chance of transferring material to the other planets in the Gliese system and, thus, is far more isolated, biologically, than the inner planets of our own solar system," says Brock. "It really shows us how unique our solar system is."