Best Chance To Find Alien Life: Rogue Planets And Steppenwolf Planets?

Does alien life exist on rogue planets? That is unknown at present, but at least one scientist believes that finding alien life, if it is to be found at all, is most likely on those parent-starless worlds wandering the universe — rogue planets.

BBC News‘ Philip Ball’s April 25 article on finding life in outer space concluded, based on work done by planetary scientists and an astrophysicist, that the most likely place to find alien life just might be rogue planets. In fact, planetary scientist David Stevenson of the California Institute of Technology — who first posited in 1999 that galaxies could be home to untold numbers of free-floating, wandering worlds untethered by the gravity of a parent star — says that rogue planets might be “the most common sites of life in the Universe.”

Ball’s article explored the idea that alien life might be found in the barren reaches of space, an area often overlooked by the media and scientists in general when speculating about the existence of living organisms outside the Earth. But it is scientifically feasible for life to not only exist in the cold vacuum of space but to also be created there. Still, it is a harsh environment and one not overly conducive to allowing the proper amalgamation of life-spawning molecules, not to mention their propagation.

That being said, how could starless worlds soaring through the vacuum of space be hospitable to life? To be so, the rogue planets would most likely need a source of heat. Turns out, there are two very important ways a starless world generate heat and perhaps harbor life as we currently understand it — internal heat and a thick atmosphere.

Each planet could be home to a fiery core, one still burning from its primordial accretion. Each world could also contain radioactive elements that, due to their decay, would warm the interior of the planet. Consider that radioactive decay inside the mantle accounts for roughly half of the total heating of the Earth. (Note: All rocky planets in the Solar System — Mercury, Venus, Earth, and Mars — have two internal heat systems.)

Stevenson suggests that a rogue planet roughly the size of Earth and capable of retaining a thick atmosphere could very well provide enough insulated heat for life to thrive on a starless world. He estimated that such an atmosphere might provide just the right temperature and pressure to allow for liquid water to form on the planet’s surface.

In addition to Stevenson’s work, planetary scientist Dorian Abbot and astrophysicist Eric Switzer at the University of Chicago calculated in 2011 that a rogue planet super-Earth, one about three-and-a-half times the size of the Earth, could sustain an ocean of water beneath an insulating frozen surface. Heat, of course, would come from the planet’s interior.

Abbot believes that the overall biological activity would be less on such a world, but life should be able to find a toehold. He and Switzer refer to these ice-crusted worlds as “Steppenwolf planets,” because “any life in this strange habitat would exist like a lone wolf wandering the galactic steppe.” They hope for breakthroughs when planned probes finally explore Jupiter’s icy moons, some of which are believed to be such small ice-covered oceanic worlds in miniature.

It is well understood that, at least mathematically, there is every reason to believe that there is alien life to be found somewhere in the universe. Thus far, however, just the possibility exists. Living organisms have proved extremely difficult to find. But if rogue planets are the answer to finding alien life, confirming its existence thereon may be a difficult prospect.

It is estimated that there are millions of rogue planets in the Milky Way galaxy alone. And they’re being discovered with more and more frequency, like the “youngest” one discovered in February that was “only” 95 light years away. Still, barring a close fly-by, direct contact with inhabitants, or discovering alien life through various astronomical detection methods, actually “finding” alien life on rogue planets (or Steppenwolf planets), although they might be the most likely sites whereon to find living organisms, could remain in the realm of science fiction for quite some time.

[Image via Wikimedia Commons]