December 6, 2010

Astrobiology – The Hunt for Alien Life

Dr Lewis Dartnell

Report by: Chris Sutcliffe

Dr Lewis Dartnell

As part of the Flamsteed Society Christmas Party evening at the Royal Observatory Greenwich on 6 December 2010, a presentation with the title “Astrobiology: the hunt for alien life” was given in the Peter Harrison Planetarium.

Dr Dartnell is an Astrobiologist from University College London, looking for life beyond Earth. Lewis is also a science journalist writing for the Daily Telegraph, the New Scientist, The Guardian, BBC News, The Sun, Astronomy Now, and Spaceflight Now, amongst others.

Astrobiology studies the search for extraterrestrial life and the effects of outer space on living organisms. How do we define ‘life’? On Earth, we know life when we see it — we have all evolved together and recognise it. All forms of known life consist of cells and Lewis showed a Harvard Biovision animated video with the title ‘A day in the life of a cell’ which can be viewed at http://multimedia.mcb.harvard.edu/

Even though we think life on Earth is familiar we continue to be surprised by how adaptable it is. Lewis describedextremophiles which are organisms which thrive in physically extreme conditions eg heat or acid. A thermophile is an extremophile which thrives in high temperatures (60 to 80 degrees C) and is found in geothermal regions of the Earth such as the Yellowstone National Park in North America.

In the Arctic, there are hundreds of pockets of water under the ice, packed with bacteria at temperatures down to -20 degrees C. There are also advanced forms of complex animal life such as tube worms which have no mouth or stomach, raising the question how do they survive. Worms have been discovered which eat ice and methane but not carbohydrates; they survive on frozen “fart gas”, in the temperature range -20 to +12 C.

So life on Earth has shown it can adapt to conditions which we now know also exist elsewhere in the solar system. Using the wonders of the planetarium’s high technology, Lewis cleverly commenced a journey from Earth starting in Greenwich, first stop Mars!

In the late 1990s, NASA’s Pathfinder Mission to Mars landed a rover on the planet to analyse Mars’ atmosphere, climate and geology, and the composition of its rocks and soil, by taking measurements and images. The expedition confirmed the feasibility of landing expedition vehicles on Mars. As a further development the European Space Agency’s (ESA) probe ExoMars is currently being designed with the aim of going to Mars in 2018 to look for signs of life. The probe will include a drill to bring soil to the surface for analysis and look for organic molecules.

Describing the cosmic radiation ionisation environment of Mars, he focused upon ‘Martian death rays’. Since the surface of Mars is unprotected by a thick atmosphere or magnetic field, cosmic rays can penetrate through several metres of rock as a result of which any life will be irradiated and probably killed.

Lewis took us on to the moons of Jupiter some of which have the potential to support life. Io has volcanic sulphur, whilst the heavily cratered Callisto has carbon dioxide, silicates and organic compounds. Europa is not too hot, and beneath its icy surface is an ocean of water; indeed it is the water-world of the solar system with the best potential for extra-terrestrial life. There is keen interest in landing a probe on Europa.

Moving on to the moons of Saturn, Titan is the largest (larger than Mercury), but its hazy atmosphere prevented us from seeing its surface. The Cassini-Huygens mission to Saturn landed on Titan and took photos through the smog to discover a landscape which in appearance is not dissimilar to the English countryside with its network of river valleys. With a surface temperature of -180 degrees C, its lakes gush with liquid methane. It may therefore have methane-based life.

Enceladus, the sixth largest moon of Saturn (but no larger than Jupiter’s moon Europa), has cracks and fissures spewing water into space which according to the results of the Cassini-Huygens mission is salty. It is a cold but potentially habitable world, and there is keen interest in exploring Enceladus with a robotic probe.

Lewis highlighted the fact that there are 400 billion stars in our galaxy of which 500 are now known to have planets, each with the potential for some form of life, and all within a ‘bubble’ of 70 light years radius.

He concluded that there must be extra-terrestrial life somewhere, and there may be other living worlds close to us. There may be the prospect of bringing cells back to Earth.

Lewis’ fascinating and thought-provoking lecture, with a “whistle stop” tour of the universe, returned us to our starting point, Greenwich.

Questions followed when Lewis described the ‘panspermia’ hypothesis which proposes that life can survive the effects of space trapped in debris ejected from the collision of objects. For example, there are 17 samples of Martian meteorites on Earth.

A great evening.

Dr Lewis Dartnell

At the start of the presentation, Tony Sizer thanked Steven Richardson (L) for his donation of filters for the 28-inch, and Mike Cowan (R) for his voluntary engineering work on the finder tube