Panspermia
Published on Mar 2, 2006 at 12:09 pm.
2 Comments.
Filed under astrobiology.
For the last couple hundred years, the idea called panspermia has been tossed around, found favor, lost favor, been revived, reviled, and then back into favor again. Basically, panspermia is the natural transferal of life from one planet to another. Recently, it has gotten another boost, which I will discuss.
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According to several internet sources, the idea of panspermia goes all the way back to a suggestion in about 450BC by the Greek philosopher Anaxagoras. However, if you look at what Anaxagoras actually said, that is really stretching things. A more modern version of panspermia can be traced back to Lord Kelvin in the 19th Century. Kelvin was responding to the work of Louis Pasteur. Prior to Pasteur, there was a concept of spontaneous generation of life. A blob of mud, for example, might become a tadpole. Pasteur showed that life comes from life, and that life does not spontaneously come into being. Together with Darwin’s work on the differentiation of species, then life could change from one form to another, but not just come into being. Kelvin extended this concept, though. Since, Earth has a finite age, there must have been some first life form on the planet. However, that might require spontaneous formation of life. So, Kelvin proposed that perhaps life in the form of microorganisms is able to cross the spaces between planets and stars. Such life might seed a new planet with organisms that could then evolve into all sorts of new life forms. This idea was further popularized by Svante Arrhenius in about 1901. Arrhenius proposed that life might exist as spores in the interstellar medium. Impacts of a planet with life might eject spores into space, where they would lie dormant until they found another planet. Anaxagoras, often credited with first proposing panspermia, really proposed something quite different. He apparently believed in atoms, the smallest division of any substance possible, and he further seemed to have a concept of atoms of life. So, he proposed that these atoms of life would fall down from the heavens and mix with either water or mud. If they mixed with water, then they formed plants. If they mixed with mud, they formed animals. This is not the same as panspermia. The only similarity was that both involved life raining down from the heavens.
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With the discovery of DNA and the chemistry of life, biologists began to accept the possibility that life could begin on its own given the right chemistry, the right conditions, and a long enough time for random reactions to yield a self reproducing molecule. The discovery of cosmic rays made it even less likely that life could survive in space. Still, as a precaution against space life, the astronauts from Apollo 11 and Apollo 12 were kept quarantined for several weeks upon their return to Earth, just in case they picked up some Moon germs. Conditions in space are very harsh. There is the vacuum, the radiation, heat, cold, and all sorts of other things. It is no wonder that the Moon is completely sterile. There is NO life on the Moon. The harsh conditions of space seemed to be the death of panspermia. Ironically, however, Apollo 12 provided some interesting results that kept panspermia alive in the hearts of its true believers. Apollo 12 landed within a short walk of the unmanned Surveyor 3 lunar lander, which had landed a little over two and a half years prior. The astronauts walked over and retrieved instruments that had sat on the lunar surface for that time. Back on Earth, at the Lunar Receiving Laboratory, in Houston, scientists found streptococcus bacteria spores in the instruments retrieved from the Surveyor 3 craft. Apparently, the instruments had been contaminated during assembly. These spores had traveled to the Moon, passing through the van Allen radiation belts, sat on the lunar surface in extremes of heat and cold, exposed to cosmic rays for two and a half years. Amazingly, the spores were viable!  Somehow, life had survived such extreme conditions. However, surviving two or three years in such environments is far different from surviving viable for millions or billions of years.
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Panspermia believers have also pointed out that in recent years we have found several example of extremophile bacteria. Bacteria have been found living on sulfur emissions from steaming volcanic vents on the ocean floor — conditions that had always been thought too extreme for life. Mold has been found growing in acid jars in chemistry labs. There are even bacteria that will live contently on the fuel rods in nuclear reactors.  Such extremophiles, panspermia proponents insist, show that life can survive harsh environments. However, there has been no evidence that even extremophiles can survive interplanetary or interstellar travel.
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Panspermia proponents point out that life began very early on Earth, and they point to panspermia as a possible seed to jump start life as soon as Earth cooled enough to permit life. Opponents, though, point out that life may simply be naturally occurring once you get the right conditions. Certainly, the classic panspermia idea of spores in the interstellar medium seeding life on planets across the galaxy seems unlikely. However, a variant of panspermia has arisen, called transpermia. While panspermia is galactic in scope, transpermia merely proposes that life originates on a planet on its own, but such life can be transplanted from planet to planet within a star system. For example, life might originate on Mars, and then be transferred to Earth, or vice versa. This is a far easier task than trying to get life from star to star. The idea of transpermia began to be taken seriously with the finding of a rock in Antarctica. This rock, labeled ALH84001 was clearly a meteorite, but was unlike most meteorites found. Careful studies showed that ALH84001 was actually a piece of the planet Mars blasted into space by a giant impact. The rock flew around the Solar System for a while before landing in Antarctica. Slicing the rock open, scientists found small nodules that reminded them of nanobacteria. They confidently announced that they thought that they may have found evidence of fossilized Martian life. Later studies by other scientists cast serious doubt on this interpretation. Most today feel that these structures are geologic in nature, not fossilized life. However, ALH84001 brought the ideas of panspermia, and transpermia in particular, to the forefront in scientific discussion. Proponents argued that while ALH84001 may not have contained life, and it may have been in space too long even for all but the most hardy extremophiles to be viable, other rocks might make the trip from planet to planet in just months or years if the conditions were right as it was ejected during an impact. Given that the streptococcus survived that length of time, and it is not known as an extremophile, transpermia seemed more likely possible if only two problems could be worked out: launching life in a massive impact without killing it, and surviving passage through another planet’s atmosphere without burning up. Neither are inconsequential problems, and seem to be the major barrier to transpermia.
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The first problem, surviving launch, is perhaps not such a problem. We know that major impacts can kick material out of the atmosphere. Many major impacts on Earth have thrown material into space, only for this material to reenter the Earth’s atmosphere and fall back to Earth somewhere else. There is even a name for these meteorites that are really ejecta from Earth impacts elsewhere. They are called tektites. I have samples of tektites (and meteorites) that I bring to my astronomy classes when we talk about meteorites. Most tektites are molten or semi-molten as they are thrown out by the impact. Clearly life could not survive these conditions. At the point of impact, the ground and the impacting body are both vaporized. Heat released in the impact melts much of the material thrown outward by the impact. The crater produced by an impact, though, is much larger than the impacting body. The outer portions of the crater are launched upward but without the heat to melt them. The acceleration produced in the excavation of the crater would seem to be much too high for live to exist intact, even for microorganisms. However, modeling of explosions from nuclear weapons shows that near the edges of the crater excavation some material is more “gently†accelerated outward in a process called spalling. In some cases, a small percentage of material is spalled and accelerated for a comparatively long time by the outer edges of the explosion. The acceleration is lower than nearer the center of the explosion, but the acceleration lasts longer, so high velocities are achieved. It is conceivable that microbes, or spores, could survive these “gentler†ejections from the planet. Then, if sufficiently hardy, and if the rock were launched onto the right orbit that it reached another planet fairly quickly, then perhaps sufficiently hardy spores might survive the trip.
This leaves reentry as a problem. For some time it has been suggested that a rock with fractures holding spores deep in the rock may shield the microbes from the intense heat of reentry. However, this is not a likely scenario. Now, a brand new finding reopens the idea of transpermia. Just over three years ago, the space shuttle Columbia broke apart on reentry over Texas. The orbiter disintegrated, and the pieces were subjected to a fiery descent through Earth’s atmosphere. The STS-107 flight was a scientific mission. Most of the science experiments burned up during reentry following the destruction of Columbia. Biologist Robert McLean of Texas State University in San Marcus, Texas, had an experiment flying on Columbia studying bacteria growth in space. His experiment had problems even before launch. One of his samples had become contaminated with microbispora. It was too late to do anything, so the experiment flew anyway. Data from that particular sample would just be unreliable is all. The rest of the experiment would be OK. Well, it turns out that his experiment package landed along with much of the other debris in Nacodoches, Texas. When it was identified, cataloged, and cleared, what was left of his experiment was returned to him. Hoping against all odds that something survived, he studied the remains. Amazingly, the microbispora survived the fiery reentry. Pretty tough little bugs, huh? His results will be published this summer in an issue of Icarus, the professional journal for planetary scientists. Panspermia proponents point to this as suggestive that perhaps life could survive reentry to another world’s atmosphere. Most meteorites come in much faster than did the Columbia, but some come up on Earth from behind, and these meteorites may be moving slowly enough to mimic the conditions that McLean’s experiment experience during the Columbia accident.
Anyway, I am making no claim one way or another about either transpermia or panspermia. I just thought that this might make an interesting blog entry.
-Astroprof
Paul on August 11, 2007 at 11:27 pm: 1
What about extemophile organisms frozen in comet ice? spores, molds fungi in the ice?
Much of the lunar surface remains unexplored. Lets get a few robot landers at the lunar poles where water could be frozen beneath the dusty surface.
janemalcomb on August 26, 2007 at 1:55 pm: 2
This little known book (link below) with the weird title will document and affirm the current scientific theories known as Panspermia Dispersion. At the end of this rather short book, reference is given to its source text, a great but poorly known scientific tome published in 1955, well before Panspermia theories were widely circulated. I feel you’d find this book fascinating, informative, and affirming to the theory of Panspermia dispersion. I highly recommend it to you.
Thanks for your time,
JPM
http://www.amazon.com/Adam-Eve-Tragic-Love-Story/dp/0741432722/ref=sr_1_2/103-7324159-3954252?ie=UTF8&s=books&qid=1188138995&sr=1-2