In 2004, the NASA spacecraft Stardust captured particles shed by the Wild 2, an icy comet in our Solar System. Last year, the team examining the Wild 2 sample discovered it contained several amino acids as well as nitrogen-bearing amines. At the time, the team was unable to rule out contamination from Earth as a possible source of the amino acids. But after painstaking tests, they were able to determine that at least one of the amino acids, glycine, came from the comet itself.

Although discoveries like this by no means prove that life on Earth originated with a comet bringing amino acids into our atmosphere, the Stardust team is excited by the implications it has for eventually explaining the origins of life on Earth. And, combined with the recent discovery that some comets contain liquid water, it seems possible that comets strikes could bring the building blocks of life to a planet's surface. The next step is to obtain larger samples from comets, and samples from the comet's nucleus instead of its debris. Fortunately, the ESA'a Rosetta spacecraft is scheduled to land on the comet 67P/Churyumov-Gerasimenko in 2014, and will hopefully bring back just the sort of sample the Stardust team is longing for.

[New Scientist]

In a paper published in the International Journal of Astrobiology, Chandra Wickramasinghe of the Cardiff Centre for Astrobiology — one of the earliest proponents of the theory of panspermia, that the seeds of life exist throughout the universe — revealed his team's calculation, which indicate that large reserves of water likely existed inside comets in our solar system, that happened to form around the same time as the Earth:

The Cardiff team has calculated the thermal history of comets after they formed from interstellar and interplanetary dust approximately 4.5 billion years ago. The formation of the solar system itself is thought to have been triggered by shock waves that emanated from the explosion of a nearby supernova. The supernova injected radioactive material such as Aluminium-26 into the primordial solar system and some became incorporated in the comets. Professor Chandra Wickramasinghe together with Drs Janaki Wickramasinghe and Max Wallis claim that the heat emitted from radioactivity warms initially frozen material of comets to produce subsurface oceans that persist in a liquid condition for a million years.

Wickramasinghe claims that a "large fraction" of the 100 billion comets in our solar system probably contained liquid interiors, with ideal conditions for the growth of bacteria, which perhaps lends greater credence to Wickramsinghe's theories on the extraterrestrial origins of life.

[Universe Today]

Panspermia is the term for the most scientifically plausible version of this concept, but it isn't necessarily what science fiction usually presents. The panspermia hypothesis holds that the building blocks of life are not found exclusively on planetary bodies but are instead found scattered throughout the cosmos, and it is these spaceborne particles that are at least partly responsible for life on Earth. There's a little circumstantial evidence for the theory (although far, far more to support the reliable old "Life comes from Earth" hypothesis), and there is something undeniably fascinating about the subtext – the aliens are already here, and we are they. But science fiction barely ever depicts the actual theory of panspermia, mostly because it's just a physical process that takes billions of years to play out and is pretty boring unless you're willing to get really mystical.

What science fiction more properly deals with is exogenesis, which simply states that humanity or its genetic ancestors didn't always live on Earth. That generally means one of two things – either an ancient alien race introduced life to a previously dead Earth (sometimes as part of a larger directed panspermia project) or a bunch of humans from some other civilization colonized Earth, a fact that somehow slipped the minds of their descendants (you know…us). Plenty of science fiction deals with both, including two of the big science fictions works currently in the news. (The occasional spoiler may lie ahead.)

Outlander
One of the most satisfying little details of everybody's favorite Vikings vs. aliens epic is its answer to why Jim Caviezel's character, the alien Kainan, looks exactly like the Norsemen and how he can possibly speak their language.Outlander solves both of these problems by revealing Earth is an "abandoned seed colony" of Kainan's spacefaring civilization. Unfortunately, the whole notion that Earth was colonized by an interstellar race really opens up a far bigger plot hole than the one it was meant to fill. After all, Kainan's people would have had to have "seeded" Earth eons ago. If they could pull off planetary engineering on that sort of scale way back then, you'd think they wouldn't have so much trouble with a bunch of bioluminescent dragons. In the end, it's probably best not to think too much about the logistics of the whole abandoned seed colony concept. Because, ultimately, the very inclusion of the idea in the first place is, like so much of Outlander, awesome.

Battlestar Galactica
In both the original and new versions of the series, humans originally came from Kobol, the legendary planet of the gods, and Earth is just the fabled lost colony. The new series is busy dealing with Earth, so it's entirely possible a couple "What the frak?" moments still lie ahead that will reveal humanity actually did come from Earth. The original series, however, left no doubt that Kobol was where we all came from, as the no-budget god-awfulness that is Galactica 1980 established contact between the Galactica and contemporary Earth. Flying motorcycle chases ensued.

Star Trek
The Next Generation episode "The Chase" sought to acknowledge and explain the genetic improbability of a galaxy full of nothing but humanoid aliens with rubber foreheads. The solution – ancient aliens who, upon finding themselves all alone in the galaxy, seeded various planets with their genetic codes – is surprisingly deft, and actually turns a three-decade failure of imaginations and budgets into something almost elegaic. As one would expect, Picard takes this existence-altering revelation in his usual stride, while the Cardassians look a bit grumpy.

Stargate
Honestly, between all the genetic engineering, forced relocations of ancient humans, and universe-altering civil wars between godlike aliens it all gets a bit difficult to keep track of which species actually came from where. In short, a bunch of plague-decimated demigods maybe used this thing called the Dakara superweapon millions of year ago to shoot their genetic information throughout the Milky Way, which maybe had something to do with humanity's evolution. Or maybe not.

Babylon 5
Since we might as well finish off the sweep of nineties science fiction, the Centauri initially tried to dismiss Earth as one of their lost colonies. Sure, this probably wasn't true, but how else are you going to haze the new interstellar species?

Isaac Asimov
Most aliens seem to create life on Earth for slightly more practical (well, relatively speaking) reasons than the Star Trek aliens' "monument to our existence." Asimov imagined Earth as an eons-old alien experiment not once but twice – in "Jokester", the aliens did it to explore the concept of humor, while in "Breeds there a Man…?" the aliens are engaged in a more vague exercise in genetics. There’s also "Death Sentence", where an anthropologist for the Galactic Federation discovers that a previous civilization created a planet of robots as part of a larger psychological experiment. Realizing the Federation will surely have to destroy the planet as a potential threat, he decides to take his dire warning to one of the robots' biggest cities: New York.

Wildstorm Comics
The Kherubim people sent their genetic seed throughout the universe in a bid to conquer the universe without their genetic descendants even knowing it, which they then followed up by actually conquering much of the universe.

Ringworld, by Larry Niven
It turns out we're all part of a larger plan by the Pak race to create a galaxy full of ultra-lethal, ultra-intelligent superhumans. Apparently, the plan failed because there wasn't enough of the right kind of fruit.

Mission to Mars
In this Brian de Palma stinker, a bunch of Martians that didn't flee their dying planet shot the neighboring Earth – then a barren chunk of rock – full of the building blocks of life because…um, because they wanted to take Gary Sinise on a tour of the universe? (And that was probably the least nonsensical part of that movie.)

Salvage Rites, by Eric Brown
One of the very few times when a race made from directed panspermia confronts their creators, this short story finds a group of Benedictine monks in a cathedral-shaped starship seeking out what is, for all intents and purposes, God.

South Park
In easily the most awesome use of the concept, the anniversary episode “Canceled” revealed Earth for what it really is – one giant reality show. At least in South Park, someone is actually bothering to watch.

Starliner, by David Drake
In this 1992 novel, the narrator explains that no one bats an eyelid at botanists cross-breeding plants from different worlds because panspermia is "no longer a hypothesis but simple observation." Not the most earth-shattering application of panspermia, but still.

Ej-es by Nancy Kress
A rather less mundane spin on that same idea, as members of an interstellar marine corps realize a deadly plague on one planet threatens all the intelligent species in the universe – because panspermia makes them all genetically related.

Doctor Who
The classic "City of Death" features a more accidental case of aliens creating life on Earth. In the midst of all the ridiculously complex art forgery, random acts of violence, Monty Python cameos, and endless location shots that prove the thing really was shot in Paris, writer Douglas Adams somehow squeezes in the origin of all life on Earth. As it turns out, an exploding Jaggaroth ship kickstarted the whole "life" thing. That was nice of them.

The Hitchhiker’s Guide to the Galaxy, by Douglas Adams
Speaking of Douglas Adams, his most famous work envisions the noblest version of the alien-built Earth. Indeed, the emphasis here is on "built", as Earth is not a planet at all but instead a ten million year old computer program supervised by hyper-dimensional mice designed to determine the question to life, the universe, and everything. Of course, as is so often the case, this wondrous philosophical pursuit was interrupted by a bunch of hairdressers, TV producers, and telephone sanitizers from the planet Golgafrincham, who obliviously managed to replace the native humans and almost wreck the entire program. All of which rather neatly leads us back to wandering, forgetful colonists.

The Hainish Cycle, by Ursula K. Le Guin
In ancient times, colonizers from the planet Hain came to Earth and, for a time, coexisted with its native hominids. Whether the settlers ultimately killed the native Earthlings or simply bred them out of existence is anybody's guess, but the Hainish now consider modern humans their descendants.

Women of the Prehistoric Planet
This MST3K entry builds a whole parable of post-War American-Japanese relations around two rival alien races, time dilation, and giant iguanas, with plenty of sixties-era chauvinism left to go around. After a whole lot of silliness (as that previous sentence probably suggested) the marooned lovers Tang and Linda settle down on the titular prehistoric planet, which they decide to call…well, I think you can guess, but it rhymes with "Mirth."

Earthsearch
The classic BBC radio series had one of the best twists on this idea, as the four teenaged survivors of the massive starship Challenger search for Earth-like planets to colonize. It's slowly revealed that the planet they call Earth has some rather unrecognizable geography, but that the Earth-like planet they finally do discover, with its saltwater oceans covering two-thirds of the planet, sounds very familiar.

The Twilight Zone
But stories don't get much more familiar than the 1963 episode "Probe 7, Over and Out." Astronaut Adam Cook finds himself stranded on a faraway planet just as nuclear war is breaking out back home. He encounters Eve Norda, an alien who cannot understand his language. The pair ultimately agrees to start a new life together on the planet that Eve keeps calling "Irth." Judging by their first names, I’m guessing they'll do just fine.

Attached to the front of a space capsule, the rock was sent into space loaded with bacteria. According to Discovery's Michael Reilly:

When the capsule hit Earth's atmosphere, the rock was heated to at least 3,056 degrees Fahrenheit (1,680 degrees Centigrade). Most of it burned away, leaving only 8 millimeters of material behind. What was left was a gooey, melted white crust of quartz. The rock's original structure — along with visible microfossils — was preserved at the core.

"This is a great positive result in searching for traces of extra-terrestrial life on meteorites," [National Center for Scientific Research scientist Frances] Westall said. "If ever Martians fossils land on Earth, we should be able to see them."

In other words, those "microfossils," or the bacteria, made it back to Earth in one piece. Even cooler, it seems this experiment also proves that Earth might be pansperminating other planets too. If our bacteria could make it into space then return to Earth, then it might also have made it offworld and crashed to Mars or Jupiter. So little chunks of Earthly bacteria might be breeding into superhumans in the upper atmosphere of Jupiter right now.

[via Discovery] Thanks, Reilly!

The theory that life can be carried between planets on rocks ejected by impacts is called lithopanspermia. Some bacteria are able to survive the cold, the dryness and the radiation present in space, especially if they're buried deep inside large asteroids (like Eros, pictured). The shock pressures produced by the impacts that would eject them into space in the first place have always been a stumbling block for lithopanspermists (they love it when you call them that).

A research team made up of German, Russian and U.S. scientists put bacteria thought to have the potential for successful space travel through some rough treatment, using explosives and air guns to slam them around in metal containers. The shock pressures used were similar to the pressures experienced by Martian rocks that were ejected by impacts and eventually reached Earth - we've found about 40 of them so far.

The results: those bacteria are pretty tough. Bacterial endospores and lichens could handle very robust shock pressures, while cyanobacteria were more fragile, but still capable of withstanding impacts strong enough for interplanetary travel. Going from Mars to Earth is a definite possibility. So if the Phoenix Lander finds evidence of past life on Mars, it could mean that all life on Earth is alien. Image by: NASA.

Microbial Rock Inhabitants Survive Hypervelocity Impacts on Mars-Like Host Planets: First Phase of Lithopanspermia Experimentally Tested. [Astrobiology]

Tardigrades have perfected an extreme form of hibernation called an anhydrobiotic state, meaning roughly that they can expel all of the water from their cells and go into a state of suspended animation. They usually only live for about a month when left in an active state, but once they dry themselves out, they can survive the harshest conditions the world can throw at them for decades on end.

Evolving to live through cold and drought makes sense — these types of conditions occur all the time on Earth. But extreme radiation? Vacuum? Some scientists believe these traits are just a byproduct of their hibernation, but in truth it remains a mystery.

Are tardigrades aliens from a distant world who came to Earth on an asteroid? Probably not — they're genetically related to the well known worm c. elegans. But last fall, the European Space Agency sent the little guys into orbit as part of the BioPan-6 mission to see how well they'd do floating above their homeworld, exposed to outer space. We're still waiting on the results of those experiments, which hopefully will shed light on why these mysterious little creatures evolved to become the toughest life on the planet.

Photo: Brett's Blog

Panspermia theories often argue that Martian mircobes hitched a ride on an Earth-bound meteor, then thrived and evolved into the life we see here on Earth. But the new findings from researchers at Imperial College London suggest the building blocks of life rather than life itself arrived from outer space. They figure that since the Murchison meteor fell to Earth bringing the molecules uracial and xanthine — precursors to DNA — there must have been a lot of this stuff pelting the planet billions of years ago.

Early life may have needed the space-born material to get started, or it could've incorporated the meteorite bits because they conferred some kind of evolutionary advantage:

Lead author Dr Zita Martins, of the Department of Earth Science and Engineering at Imperial College London, says that the research may provide another piece of evidence explaining the evolution of early life. She says:

“We believe early life may have adopted nucleobases from meteoritic fragments for use in genetic coding which enabled them to pass on their successful features to subsequent generations.”

Between 3.8 to 4.5 billion years ago large numbers of rocks similar to the Murchison meteorite rained down on Earth at the time when primitive life was forming. The heavy bombardment would have dropped large amounts of meteorite material to the surface on planets like Earth and Mars.

Either way, it looks like we're made of space stuff.

Source: Imperial College London

Previous experiments have shown that microbes can survive in the punishing cold of space. Their ability to hide out in a rock's interior, safe from a vacuum is well-documented too.

But scientists haven't been able to tell whether hearty critters could survive the heat and crushing force of an asteroid impact that would be needed to eject them into space in the first place. Astrobiologists at the Institute of Aerospace Medicine in Germany have finally connected all the dots with a new experiment in the Spring issue of Astrobiology Magazine

And what better way to simulate an asteroid impact than to smash rocks together? That's exactly what the scientists involved in this research did, after sprinkling test rocks with bacteria known live inside stone, some cyanobacteria, and a dash of lichen onto them. All three lifeforms survived the high-speed collision, suggesting they could be floating through outer space even now, waiting for a chance encounter with distant planet to plant the seeds of a whole new 'alien' biosphere.

Source: Astrobiology Magazine

Image: NASA

The data fits with the extinction of the dinosaurs 65 million years ago and another extinction at the end of the Paleocene period, 35 million years ago. It also means our planet's probably in for another life-ending black eye in the not too-distant future.

But what's Galactic density got to do with comet impacts? As the solar system moves through denser parts of the galaxy the extra gravitational pull upsets comets orbiting the Sun, sending them hurtling towards Earth. The theory's been tossed around for a while (and there are other good ones, like supervolcanoes, that haven't been discounted yet) but this new evidence makes it seems a little more believable.

It sucks to think that gravity — a pretty immutable force of nature — will be the source of our demise rather than something we can avoid, like global warming or nuclear war. But the study suggests there may be a silver lining to our extinction: comet impacts could be the driving force behind panspermia:

While the "bounce" effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.

Centre director Professor Chandra Wickramasinghe said: "This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale."

Source: Cardiff University via Science Blog

Image: The Alien Next Door