SETI [ASTRO] Many Life-Bearing Planets Could Exist In Interstellar Space

Larry Klaes (
Thu, 01 Jul 1999 16:23:22 -0400

>X-Authentication-Warning: majordom set sender to owner-astro using -f >Date: Thu, 1 Jul 1999 15:35:32 GMT >From: Ron Baalke <> >To: >Subject: [ASTRO] Many Life-Bearing Planets Could Exist In Interstellar Space >Sender: >Reply-To: Ron Baalke <> > >Caltech > >Contact: Robert Tindol, (626) 395-3631, > >June 30, 1999 > >Many life-bearing planets could exist in interstellar space, according to >Caltech planetary science professor > >PASADENA -- Long ago in a solar system not at all far away, there could >have existed about five to 10 Earth-like planets in Jupiter-crossing orbits. > >These planets today could harbor life somewhere in interstellar space, >according to a planetary scientist at the California Institute of Technology. > >In the July 1 issue of the journal Nature, Caltech professor Dave Stevenson >says in a new study that such objects could be life-sustaining due especially >to the molecular hydrogen they accreted when the solar system formed long >ago. > >Called "interstellar planets" because they would exist between the stars but >no longer in orbit around an original parent star, they have never been directly >observed or proved to even exist. But based on what scientists know about >the way matter should fall together in forming a solar system, such Earth- >like planets could definitely have been formed. > >Over a period of several million years, one of two things happened to these >planets: either they slammed into Jupiter and made it even bigger, or else >they came so close to Jupiter that they were catapulted by gravity >completely out of the solar system, never to return. > >Because these bodies formed when the solar system was permeated with >hydrogen gas, they retained a dense atmosphere of hydrogen, allowing them >to have surfaces with temperatures not too different from Earth, and >possibly water oceans. > >Stevenson writes that in the absence of sunlight, the natural radioactivity >inside an Earth-like planet would only be sufficient to raise the radiating >temperature of the body to 30 degrees above absolute zero (that's about >minus 400 Fahrenheit). But the expected dense hydrogen atmosphere would >prevent the surface from radiating effectively -- just like the greenhouse >effect on Earth, but more so. > >As a result, the surface could have a similar temperature to the current >Earth surface, allowing water oceans and a surface pressure similar to >that at the bottom of Earth's oceans. For this to happen, the interstellar >planet would probably need to be at least half Earth's mass. > >Therefore, the energy source would be much the same as that which drives >geothermal energy and plate tectonics on Earth. > >It is not known whether geothermal heat alone is sufficent to allow life >to originate, and the amount of energy is small compared to sunlight, >suggesting that the amount of biological activity would also be small. >But the existence of life in such an environment would be of great interest >even if the mass of living matter were small. > >The heat energy, and especially variations in temperature, could potentially >allow life to get going, Stevenson says. > >"I'm not saying that these objects have life, but everyone agrees that life >requires disequilibrium," he says. "So there has to be a way to get free >energy, because that's what drives biochemical processes. > >"These objects could have weather, variations in clouds, oceans ... even >lightning." > >If life exists on such objects, an open question is how complex it could >be, Stevenson says. "I don't think anyone knows what is required to drive >biological evolution from simple to very complex systems." > >These interstellar wanderers could also have arisen as a natural outcome >of the formation of stars, and not just during the formation of the system >we live in. In either case, such planets cannot be seen with present >technology because they are so dark and cold-at least from Earth's >vantage point. > >Although these bodies may have warm surfaces, they would appear to us >as very weak emitters of long-wavelength infrared radiation, much below >current detection limits. > >The best bet for even demonstrating that interstellar planets exist is to >have some programmed search for occultations, he says. In other words, >the object might pass occasionally in the direct line of sight between >Earth and a star, and if instruments were watching, the light of the star >might dim or even flicker out for a time. > >Programs like this are already advocated for the purpose of looking for >planets in orbit around other stars. But looking for interstellar planets >would be even harder. > >"All I'm saying is that, among the places you might want to consider for >sustainable life, you might eventually want to look at these objects. They >could be the most common location for life in the universe." > >RELATED LINKS > >* Dr. David J. Stevenson > >* The Division of Geological and Planetary Sciences at Caltech > >* Nature > > >

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