suggests life on Earth may have been seeded by meteorites

The microbes on-board Endeavour include the Tardigrades (nicknamed Water Bears) which are large extremophiles that can withstand temperatures as biting as absolute zero, and as hot as 150 degrees Celsius. They're joined by the Deinococcus radiodurans (which Nasa dubbed " Conan the Bacterium") which can survive upwards of 15,000 gy of radiation -- 10 gy is more than enough to kill an average human.



Following days of delays and numerous technical issues, Endeavour is finally ready to ferry six astronauts to the International Space Station. During their 16 day trip the Nasa researchers will drop off a $2 billion Alpha Magnetic Spectrometer, which has been designed to study the formation of the Universe and search for evidence of dark matter and antimatter.

But there are also some other passengers on the shuttle, who might not receive the same media attention, sew-on patches and victory parades. Alongside the all-male crew of mission STS-134, six types of microorganism and a bobtail squid will strap in their seat-belts and head into space.

The five microorganisms will blast off on behalf of The Planetary Society's Living Interplanetary Flight Experiment (LIFE), which will see if living organisms can make the trip into space, handle some zero-G exposure and take in a little low Earth orbit radiation.

The experiment would investigate the transpermia hypothesis -- which suggests life on Earth may have been seeded by meteorites ripped off the surface of other planets like Venus or Mars. Whether or not the microbes can survive the ordeal would go a long way towards proving or debunking the controversial theory.

The microbes on-board Endeavour include the Tardigrades (nicknamed Water Bears) which are large extremophiles that can withstand temperatures as biting as absolute zero, and as hot as 150 degrees Celsius. They're joined by the Deinococcus radiodurans (which Nasa dubbed " Conan the Bacterium") which can survive upwards of 15,000 gy of radiation -- 10 gy is more than enough to kill an average human.

Haloarcula marismortui (Old Salty) loves salt, and lives in levels of high salinity that would kill other organisms. Pyrococcus furiosus (Fire eater) is all about heat, and thrives in temperatures over 100 degrees Celsius. Cupriavidus metallidurans (which doesn't have a nickname, unfortunately) plays a vital role in the formation of gold nuggets, thanks to its love of gold tetrachloride: a compound which is toxic to most other microorganisms.

Finally there's Bacillus subtilis (The Average Joe), which is a model organism used in hundreds of biological experiments. It's been into space many times before, so it'll be a good comparison point for other studies.

This group of differently-skilled organisms is actually just a dress rehearsal for the real deal. LIFE's next mission will be sending microorganisms to Phobos, the dusty innermost moon of Mars, to really put the transpermia hypothesis to the test. A second batch of microbes will take flight on Russia's Fobos-Grunt lander, which will jet off towards the red planet in November 2011, and return to Earth with samples in the summer of 2014.

Space-faring microorganisms are so Apollo-era, though. So, here's something new: the bobtail squid Euprymna scolopes will be the first cephalopod in space.

The experiment is less about the squid and more about the beneficial bacteria that skitter about in the sea creature's body. Handy Vibrio fischeri microbes live in the squid's organs, and the animal uses the bacteria to generate light which is cast downwards to blot out its own shadow.

Considering the way that some bad bacteria turn even nastier when subjected to the extreme temperatures and radiation of outer space (in 2007, Salmonella bacteria were three times more likely to kill their host mice after returning on a shuttle), Nasa wants to see what happens to mutually beneficial microbes when they're in space. Will good bacteria turn bad?

The baby squid on board Endeavour will be colonised with bacteria, and then it will be killed and fixed solid for examination back on Earth.

Once Endeavour's payload is delivered, there is only one shuttle flight left in the program. The shuttle Atlantis will blast off on mission STS-135 on 28 June. After that, Nasa will look to privately funded firms like SpaceX to carry out future missions.