Re: SETI [ASTRO] Many Life-Bearing Planets Could Exist In InterstellarSpace

Alfred A. Aburto Jr. (
Thu, 01 Jul 1999 20:08:25 -0700

Interesting, But I thought that such a small planet as Earth could not hold on to her premordial hydrogen gas? The hydrogen gas molecules move around fast enough that the hydrogen gas soon evaporates into space? The gravitaional field of the Earth is too weak. It would take a big planet like Jupiter to hold onto its original hydrogen! The article appears to miss the above important point... Al Aburto > Larry Klaes wrote: > >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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