exosci.com / Thursday July 01, 1999
Lost in Space

A report in Nature is provoking discussion amongst those involved in the search for extraterrestrial life. The report, written by David Stevenson, proposes that small, rocky planets similar to the Earth can be ejected from their solar systems during formation, and that these rogue planets could support life.

Stevenson, of the California Institute for Technology, says that these small planets could be kicked out of their solar system during formation due to the gravitational effects of larger nearby planets. The ejected planets could harbour a hydrogen atmosphere. Such an atmosphere, if it were sufficiently thick, could help retain heat and may even permit the formation of surface liquid water oceans.

Since these rogue planets would be quite distant to any stars, any life on them would have to rely on energy sources other than direct sunlight. Stevenson writes, "if life can develop and be sustained without sunlight (but with other energy sources, plausibly volcanism or lightning in this instance), these bodies may provide a long-lived, stable environment for life (albeit one where the temperatures slowly decline on a billion-year timescale). The complexity and biomass may be low because the energy source will be small, but it is conceivable that these are the most common sites of life in the universe."

Last year there was some excitement over the discovery of potential rogue planet (TMR-1C), but this finding has been shrouded in controvesy as of late. Scientists suspect the 'planet' is actually a small star.

Stevenson admits that his proposal is almost impossible to prove. "To be frank, I debated whether to submit this (for publication). In the end I decided that ideas play an important role in science, even when they don't have an immediately testable aspect," said Stevenson.

-David Watanabe