In the fiftieth anniversary since the first attempt to search for radio signals from alien civilisations, pre-eminent scientists from the worlds of astrobiology and astronomy have convened for a special meeting at the Royal Society in London both yesterday and today to thrash out where the Search for Extraterrestrial Intelligence (SETI) currently stands.

“Our working number is 10,000 detectable civilisations in the Galaxy,” says Dr Frank Drake of the SETI Institute. Drake, who initiated the search for extraterrestrials in 1960 with Project Ozma, calculates this figure from his famous Drake Equation, which purports to estimate the number of civilisations out there based on a number of astrophysical, biological and evolutionary factors. “While that figure is exciting,” he adds, “It means only one in ten million stars have extraterrestrial civilisations orbiting them. To have a chance of finding them that means we have to search at least ten million stars.”

Not everyone agrees with Drake’s figure. Professor Simon Conway Morris of the University of Cambridge, who gave a presentation at the meeting entitled ‘Predicting What Extraterrestrial Life Will Be Like... And Preparing For the Worst’, is dubious, believing that life on Earth is a fluke never to be repeated. “In my opinion there is nothing out there at all,” he says. And should he be wrong, and we do get a radio call from someone else out there, he believes we shouldn’t reply. Certainly in human experience, whenever a more technological civilisation has encountered a less advanced civilisation (for instance the Europeans and the Incas) the less-advanced civilisation has always come off worst.

In the meantime, our search for extraterrestrial life is focusing on our own Solar System, and Professor Charles Cockell of the Open University perfectly summed up the challenge that we are facing. He argues that the definition of a life inhabited biosphere is “self-aggrandising nonsense” and that the term ‘biofilm’ is more accurate: a tenuous, incredibly thin veneer on the outside of a planetary crust (the lithosphere) that life can gain energy from to survive. This biofilm is trapped between the freezing abyss of space and the searing hell of a planet’s interior. Ironically both volcanism from the “searing hell” below and comet and asteroid impacts from the “freezing abyss” both have roles in improving the development of the biofilm in the long run.

To find life on other worlds, Cockell advocates “following the kinetics”. By that he is referring to energy for life derived from hydrothermal processes, i.e. flowing water, weathering of rocks, and heat from geological processes underground. The bad news is that there is no kinetic hydrothermal cycle to be found in comets or icy asteroids, which have long been purported to be carriers of primitive life. “I don’t think the interior of comets would be a very good place for life,” he says.

Nonetheless, the building blocks of life may have their origins amongst the stars, says Professor Pascale Ehrenfreund of the George Washington University in the United States, and also Leiden Observatory in the Netherlands. Her presentation at the meeting concentrated on the creation or organic carbon-based molecules in interstellar environments such as gaseous stellar remnants and protoplanetary discs.

“Interstellar clouds and circumstellar envelopes act as formation regions for complex molecules,” she says. “Organic molecules that are able to survive include polycyclic aromatic hydrocarbons (PAHs) that are seen in the infrared spectrum of distant galaxies. So the building blocks of life must be widespread in planetary systems in both the Milky Way and other galaxies.” Indeed, she revealed that the signature of carbon molecules in the form of dust has been detected as far back as 13 billion light years, just a few hundred million years after the big bang. This material eventually wound up on planets, and on at least one of those planets – Earth – it has organised itself into complex, intelligent life.

Another world where these building blocks may have organised themselves into simple, if not intelligent, life is Mars. NASA’s Dr Chris McKay gave two reasons for searching for life on Mars (as well as looking on Europa, Enceladus, Titan, and even the atmosphere of Venus) in his talk. First, discovering life elsewhere in the Solar System will make us more confident that life is common; and second, it will allow us to do comparative biology, comparing creatures that have a completely separate origin to that of life on Earth. He’s not talking about whether they have scales or feathers, but about their biochemistry on an internal, microscopic level. That means potential fossils of Martian microbes reputedly found in the Martian meteorite ALH84001 wouldn’t really be much help as they couldn’t tell us anything about the biochemistry of the microbes that formed the fossils, or whether they really did originate in a second independent genesis of life.

“We need to find a Martian corpse instead!” says McKay. To this end, he advocates that searching the red planet’s polar regions is the best bet. The Phoenix has probe has already visited the north polar region, finding water–ice just below the dirt, and perchlorate mixed into the soil. Perchlorate is an important finding because it acts as an anti-freeze. Mars’ axial tilt can wobble wildly; today it is 25 degrees, but five million years ago it was 45 degrees and Mars’ north pole would have received much more sunlight than it does today, making it warm enough for a liquid water brine containing perchlorates to flow across the surface. The evidence for this has already been found by Phoenix – the ice that it uncovered was separate from the dust around it. Such segregated ice is found on Earth where liquid water has run. Interestingly, McKay also points out that perchlorate would have hidden the signs of organic molecules from the Gas Chromatograph Mass Spectrometer experiment onboard the Viking landers in the 1970s. Perhaps it is time to return to Mars and to renew search for life with more advanced experiments.

After the astrobiology-dominated first day, the second day of the conference promises to look more at the search for intelligent life, or SETI. Stay tuned for a full report!

For more information about life on Mars, pick up our Mars-themed February issue of Astronomy Now, and for related information about SETI, read our interview with Professor Paul Davies or pick up a copy of our 2010 Yearbook, available from our online store.