By Robert Roy Britt
Nestled safely inside the belly of a comet orbiting some unknown star, a microscopic alien sits dormant. Somewhere in this vast universe — perhaps a place like Earth — a greater destiny awaits the microbe. A place to flourish, become a nematode or a rose or a teenager.
Life, after all, is tenacious and thrives on change.
Over time, gravity performs a few plausible, but not routine tricks, and the comet is ejected from its stellar orbit like a rock from a slingshot. For more than a 100 million years it slips silently across the inky vastness of interstellar space.
Then gravity goes to work again. Another star tugs at the comet, pulls it in.
A few giant gaseous planets whiz by, their bulks tugging at the comet, altering its course slightly. Ahead now, growing larger, looms a gorgeous blue and brown marble. Water and land. Maybe some air. that a space rock could successfully transport life between planets.
Another group of researchers, reporting in the October 19 issue of Nature, claims to have found and revived bacteria on Earth that were dormant, in the form of spores, hiding in New Mexican salt crystals for 250 million years. Scientists called the implications of this second discovery profound, suggesting that if further study bears out the findings, it could mean bacterial spores are nearly immortal.
And if you are immortal, then what are a few billion years of interstellar travel?
“Until recently, panspermia was not even regarded as a scientific hypothesis,” says Chandra Wickramasinghe, the concept’s leading proponent. “Now that has changed.”
In interviews with more than a half dozen respected scientists in diverse fields, it’s clear that panspermia, or at least some aspects of the theory, is poised to jump to the forefront of study among scientists who seek to understand where and how life began. While the prevailing theory holds that life arose spontaneously out of a terrestrial, chemical soup, panspermia’s defenders argue that such a miracle could happen almost anywhere.
This means we could have microbial ancestors, or even more evolved cousins, in unexplored corners of the cosmos.
“Both (new) studies lend a healthy boost to the plausibility of panspermia,” says Jay Melosh, a geophysicist at the University of Arizona’s Lunar and Planetary Laboratory. “I just submitted a paper to (the journal) Icarus that says that an interstellar journey is overwhelmingly improbable. However, a number of factors — including the recent Nature article — are making me rethink this.”
Like other scientists, Melosh still calls the interstellar transfer of life improbable, but expects research into the idea to ramp up.
Then with the force only the cosmos can summon, the comet slams into the third rock from a mid-sized, moderately powerful star. The alien microbe survives, emerges from its protective shell and spreads like the dickens.
Thus began life on Earth, 3.8 billion years ago.
Or so goes one aspect of a theory called panspermia, which holds that the stuff of life is everywhere and that we humans owe our genesis and evolution to a continual rain of foreign microbes. It means, simply, that we might all be aliens.
It’s an idea that has been around longer than Christianity, but which still struggles to gain strong support among most scientists.
But two recent discoveries are breathing new life into the theory.
One study, reported in the October 27 issue of the journal Science, shows.
Panspermia: Its own origins and evolution
The idea that the seeds of life are ubiquitous throughout the cosmos goes back to Anaxagoras, a Greek philosopher. In the 1800s, French chemist Louis Pasteur proposed that spontaneous generation of life could not have occurred on Earth. British physicist Lord Kelvin and others jumped on Pasteur’s bandwagon and suggested that life might have come from space.
But modern-day panspermia advocates have been the Rodney Dangerfields of science.
In fact, just two leading researchers carry the bulk of the panspermia torch. The renowned Sir Fred Hoyle, known for his studies of star structure and the origin of the chemical elements in stars, has worked with Chandra Wickramasinghe over the past three decades to pioneer the modern theory of panspermia.
In the 1970s, Wickramasinghe and Hoyle found what they say are traces of life in the dust around distant stars. The duo then broadened the panspermia theory, arguing that a continual rain of life-altering stuff from space — including germs that arrive in cycles related to solar activity — has affected the course of evolution. The seeds, they say, are still coming.
Support for parts of panspermia
Other researchers agree that both space rocks and comet dust might in fact harbor organic matter. But how these ingredients for life might travel from one star to another is hotly disputed.
Even as doubters are beginning to give panspermia advocates a little respect, most say the likeliest transfers of life would occur between planets.
“That bacteria, or at least their spores, can survive for such staggering amounts of time makes their transport from planet to planet on meteorites possible,” said Matthew Genge, a meteoritic researcher at the London Natural History Museum. “Bacterial spores in their very own kind of suspended animation could perhaps survive the millions of years it takes for rocks to travel from planet to planet.”
But Genge, along with other scientists, cautioned that the 250-million-year-old bacteria found in New Mexican salt crystals are not conclusive. There is a chance the samples were contaminated with more modern bacteria, and follow-up studies need to be done. last year’s discovery of living microbes deep in the Antarctic extends the range of extreme conditions under which life is known to survive.
Still, previous studies have found viable bacterial spores in 30 million-year-old amber. And
Few researchers question that life is hardy, and that it can hang on for a very, very long time. And some space rocks are known to make the trip from Mars to Earth in less than a year.
The trick for a much lengthier interstellar journey would be surviving deadly cosmic rays.
Even the nearest stars known to have planets are many light-years away. And none has been shown to have habitable planets. Some nearby stars are becoming more interesting, however. The star Iota Horologii, just 56 light-years away, is the first to have a planet in an Earth-like orbit and to show other signs of solar system formation like our own.
But even 56 light-years is a bit longer than your average commute.
“Herein lies the problem,” Genge said. “In Earth rocks, bacterial spores may survive for millions of years cocooned beneath the Earth’s surface because they are protected from radiation. On a meteorite in space, fast moving atomic and sub-atomic particles will plow through the meteorite like cosmic cannon balls. If they encounter an organism, DNA molecules will be shattered. If hit enough times, the organism will not survive.”
Several scientists suggest that to survive, a spore, seed, bacteria or other organism would need to be imbedded deep inside a good-sized space rock, perhaps 3 meters (10 feet) or larger, shielded from radiation. Even then, there is the problem of launching a star-orbiting rock or comet into interstellar space.
The only way to do this is through repeated, and tricky, gravitational interactions with planets, says Genge, explaining a process like the one NASA used to sling the Voyager spacecraft out of the solar system.
“The thing is, it’s taken a lot of very clever people, powerful computers and cutting-edge technology to do this,” Genge says. “Terrestrial meteorites are just rocks and even with microbial passengers they are pretty stupid and thus have to rely on chance.”
Somewhat lost in the current panspermia revival is the intriguing flip-side of the “ubiquitous life” idea: If life could have come here from somewhere, why couldn’t an Earth rock have been dislodged long ago, sending life to another planet or star system?
“It is possible that there are small fragments of the Earth out there in space today, some with microorganisms, that were blasted off the Earth’s surface many millions of years ago,” Genge says. “These could reach the Jovian moons and through extreme good fortune seed the water oceans with microorganisms.”
Okay. How likely?
“The chances of this happening in reality are probably similar to someone finding their way home after being blindfolded and airlifted to another continent.”
Genge and others say the more plausible scenario for the transfer of life — if it has ever occurred and given the scant solid evidence currently available — is that it started on Mars and came to Earth. The recent discovery of water beneath the surface of Mars has researchers in many fields excited, suggesting that any life that was once there might still exist.
“I consider it almost inevitable that microorganisms have been transferred between Mars and Earth by hitching a ride deep inside rocks blasted off the surface by asteroid impacts,” says physicist Paul Davies, author of The Fifth Miracle: The Search for the Origin and Meaning of Life.
While Davies says life could have moved in either direction, the Mars-to-Earth scenario is his favorite, based on presumed state of things a few billion years back.
“Mars was a more favorable environment for life to get started,” Davies told SPACE.com. “Being a smaller planet than Earth, it cooled quicker, so the comfort zone for deep-living organisms (the ones safe from impacts) was deeper sooner. It is easier for rocks to go from Mars to Earth than vice versa, because Mars has a lower gravity.”
Davies is rock-solid in his belief that it takes rocks, serving as protective vessels, to move life from one planet to another. He rejects the idea that “individual microbes waft naked through outer space” — one of the original tenets of the panspermia theory.
“I still believe it exceedingly unlikely that life could hop from one star system to another that way, largely because of the radiation hazard,” Davies says. “It is possible for such transfer to happen inside rocks, but the chance of a rock blasted off Earth ever hitting another Earth-like planet beyond our solar system is infinitesimal.”
So does this kill the idea that life on Earth arrived from another star system, that we might have distant ancestors — or maybe even cousins — waving to us from an orbit around Iota Horologii?
“Clearly it’s possible,” Davies says, “but the odds are exceedingly low.”
Wickramasinghe, the primary panspermia proponent, responded with a different view:
“Not all microbes in interstellar space would survive of course,” Wickramasinghe said. “But the survival of even a minute fraction of microbes leaving one solar system and reaching the next site of planet formation would be enough for panspermia to be overwhelmingly more probable than starting life from scratch in a new location.”
So despite all the new and important discoveries, we still don’t know how or where life began. But the search for it has gotten a little more interesting, now that we know we might all be aliens.
Source: Space.com, October 30, 2000
