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.

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.

Possible Martian bacteria fossils in a meteorite found in Antarctica. The rock, by keeping its cool, could have sustained life during its travels.

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."

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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.

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.