Are we close to finding life off Earth?

Kepler, Nasa's planet-hunting spacecraft, has clocked up 1,235 new planets to date – could it eventually find one with the conditions needed to spark life, writes JOHN HOLDEN

LIFE ON Earth was an unlikely outcome. The conditions required for life to evolve have been described as the Goldilocks Effect – everything has to be just so, not too hot, not too cold, not too dry, not too wet. In fact, the specific environment needed to make life possible is so exacting it would take a very modern Goldilocks to define them.

The Goldilock’s Effect refers to the size, scale, mass, atmospheric conditions and distance from our star (the sun) that must combine in order for Earth to harbour life. And with no other existential reference point to use, the search for life elsewhere is measured using the conditions under which life on Earth has come about.

The Kepler spacecraft, which was designed by Nasa specifically for extra-solar planet hunting, has been on two missions so far and has clocked up 1,235 new planetary candidates in our galaxy alone. Simply put, the more planets found the more likely one of them will have the conditions necessary to spark life.

“Kepler uses a technique called ‘transit’,” explains Lorraine Hanlon from the UCD school of physics. “It monitors the brightness of a star and, when that star’s light dims, you can deduce that something has passed in front of it. The bigger the dip, the bigger the planet.”

The planet’s orbit length can then be figured out by measuring how long the light is dimmed for.

The transit method has also been used closer to home, albeit with different technology. Professor Don Pollacco and his team in Queen’s University Belfast are responsible for the discovery of 60 planetary candidates of their own. “We use ground-based facilities – the Super Wide Angle Search for Planets, or ‘Superwasp’, with data collected from optical telescope observatories in the Canary Islands and South Africa,” explains Pollacco.

“To confirm the motion of a star with a planet orbiting it is an incredibly difficult thing to do. The motion is so small.” It’s easy to forget that the Earth doesn’t just orbit the Sun, but that both are orbiting a common central mass. “It’s like two ice-skaters,” says Pollacco. “But with the transit method you could be measuring ten centimetres per second’s worth of movement, which is a tiny velocity to be calculating.” This painstaking appraisal is not helped by the Doppler Effect.

“Because the star and planetary candidate are both orbiting around a point, this gives the star’s light a wobble effect,” says Hanlon. “We call this a ‘stellar wobble’ or Doppler Effect which changes as it orbits the star.

“It’s not unlike the change in frequency of an ambulance siren as it comes closer to you and then further away.” Planet hunters at NUI Galway use yet another approach with their locally designed optical photometer.

“The Galway Ultra fast Imager [GUFI] is capable of taking extremely fast low-resolution photos,” explains Leon Harding of NUI Galway’s Centre for Astronomy. “It can take anything from 30-526 frames per second. It’s capable of very effectively sampling any light variations on its surface.”

GUFI is stationed at the University of Arizona on the two-metre Vatican Advanced Technology Telescope. It’s run by a group of Jesuit astronomers,” says Harding. GUFI has been stationed since May 2009 and the observatory is so happy with its performance so far that the NUI Galway team have just successfully negotiated a third year of operations.

Using “transit” and other light-measuring methods tell us something is orbiting a star but then follow-up observations are needed to verify if it is in fact a planet at all. The primary Goldilocks indicator usually sought is its size and distance from a star.

“Our sun is perfect for us,” explains Leon Harding of NUI Galway’s Centre for Astronomy. “It’s right in the middle of its own lifetime and is not too active because solar weather can be very destructive.

“In 2010 the strongest possibility of a terrestrial exo-planet was found,” says Harding. The rather blandly named “Gliese 581 g” planet was believed to be likely to have the right conditions for liquid water to exist, based on its distance from a star. Further analysis needs to be conducted on this planet’s life-harbouring prospects but it still remains one of the best candidates around.

While Kepler is yet to find evidence of conditions that are just right for life to exist, the increasing numbers of extremophiles being found on Earth makes the chances for simple life, at least, to exist elsewhere more likely.

These organisms thrive in extreme temperatures, acidity, radiation and other harsh environments. Acid pools, Antarctic permafrost and volcanoes are just some of the places extremophiles call home.

With the existence of extremophiles in places on Earth almost as alien as space, some experts believe they are not far off from finding ideal terrestrial exo-planets. “Within a year from now, I believe the Kepler project will have discovered at least one or two Earth-sized objects with the right distance from a star,” says Pollacco.

“The spacecraft has been flying for two years and has completed its second mission. But three observations are needed to be sure.” This is not to say that Kepler and other planet-hunting exercises haven’t already made spectacular discoveries. “What Kepler and our research really tells us is the sheer volume of planets there are out there in the universe,” says Pollacco. “We’ve seen planets as dense as metal, and others as dense as water.

“Kepler has also found a number of completely aligned multiple planet systems. In our solar system the planet’s orbits are not aligned but we’ve found one system with six planets that are aligned to within half a degree of each other. No one understands why this could be the case.”

CONAN THE BACTERIUM

Meet Deinococcus Radioduran(pictured above), or Conan the Bacterium to his mates. This simple life-form would make mince meat of Bear Grylls on an assault course. It can withstand extreme cold, dryness, very low PH levels and cosmic radioactive intensity.

Conan is just one of a number of extremophiles found in some of the harshest and most uninhabitable places on Earth. Scientists now understand that some simple life forms are able to defy many of the basic principles previously thought necessary for life to exist.

“The acidophile is a type of bacteria found in acid streams with a PH level below 1,” explains biologist Chris Allen from Queen’s University Belfast. Acid of this nature would burn a hole through a human hand and yet acidophiles live in acidic pools, geysers and even in areas polluted by acid mine drainage.

The list goes on. “We also have extreme halophiles which like to live in salt,” says Dr James McInerney of NUI Maynooth. “The Red Sea is red because it’s full of halophiles. Then you have hyperthermophiles which live in the black smoke that spews out of hydrothermal vents,” he adds.

“Some of them thrive at temperatures higher than boiling water.”

In fact, extremophiles can be found everywhere. “If you drilled a hole two kilometres into the Earth’s crust and sampled the sediment, you would find living organisms using hydrogen as a source of energy,” says Allen. “There are very few sterile places on Earth.” What this means for terrestrial planet hunting is that “life” doesn’t necessarily need to fit the narrow criteria that have previously been set.

“The limits of life on Earth are much broader than we first thought, so this increases the probability for the potential of life to thrive elsewhere,” says Allen.

If nothing else, Conan the Bacterium is testament to this.

“Even if you exposed this organism to radioactivity in a nuclear power station, it would still be well below the threshold it could withstand,” says Allen. “It could probably survive in outer space on the side of a spacecraft.”