Tuesday, 6 October 2015

We are not alone

Today we travel! Not to Cork but to the limits of the detectable universe. We used to think that man was crafted in the image of god and given dominion over all he surveyed. That legitimised the subjugation of women, eating of animals, and a general feeling that, if you had XY chromosomes, two legs and ten fingers you were the centre of the universe. I wrote about how, four hundred years ago, Galileo shook this quaint conceit rather sharply when he realised that the planet Jupiter was not a speck of light circling somewhat eccentrically round the Earth. It was, au contraire, a world of its own with more moons than we had.  That was a bit of a shock but we assimilated the information and readjusted the story while continuing to sack the planet to supply us with toys and grossly inappropriate food-stuffs. The 20th century saw us relegated further and further from the centre: of the solar system, of the galaxy, of the universe. That was because better instruments, better theory and better algorithms enabled us to accumulate data about what was out there beyond the atmosphere.

Mina Fleming and Annie Jump Cannon, girl-astronomers of quite shocking dedication and insight processed the data in ways that helped predict how far, how big and how hot was each pinpoint of white on a million photos of the dark night sky.  From these catalogues of stars Frank Drake could calculate how many of the stars were sufficiently sun-like that we could imagine them supporting some sort of life on a planet nearby. But in 1961, Drake just had to wave his arms vigorously to estimate how many of the sun-like stars might have planets. Our well-planetted solar system might be boringly typical or deeply different but with a sample of one we had no way of getting better information. In 1992, a generation after Drake, Wolszczan and Frail found evidence of something whirling round a pulsar that might be a planet.  But as Jocelyn Bell Burnell has been pointing out since she discovered pulsars LGM-1 and -2, being up close and personal with a pulsar is far too extreme to encourage life-as-we-know-it: the emitted radiation would make your hair stand on end.

The real break-through came exactly 20 years ago today when Michel Mayor and Didier Queloz at the University of Geneva revealed the existence of a planet in orbit round the star 51 Pegasi [R for red in the bottom left corner of the square made by α, βand γ Pegasi and α-andromedae]. These are known more romantically by their Arabic names of Markab the saddle; Al Sā’id/Scheat the upper arm; Algenib and Alpheratz/Sirrah. 51 Pegasi was a 'main-sequence' [ie normal] star about 50 light-years distant and although its planet was much larger than Earth, it seemed possible that life could exist on or near its surface.  The tools available to Mayor and Queloz meant that only big star-gravity-perturbing exoplanets were capable of being detected. As techniques and equipment have improved over the last 20 years, these 'hot Jupiter' lumps are found to be the exception not the rule.

About 2000 planets have been convincingly demonstrated by a variety of clever detection methods requiring a knowledge of physics that is beyond me.  One way is to detect a separate infra-red [hot] source of light next to a star. This is like trying to distinguish a warm baked bean from a searchlight 50m away from a spot at the edge of the solar system. The other method relies on the fact that planets do not rotate about their star; both objects rotate about their collective centre of gravity. You can pick up the doppler shift of the light as the star is swung in to and from the observer by its minute rotating partner: think an enormously fat man man being swung around by a new-born kitten. Doubtless the methods used to detect these remote and tiny fluctuations in light are being used to track your every movement by The Man's all-seeing-eye geostationary satellite.

Just like we should see the arrival of a couple of thousand Syrian and Somali refugees in Ireland as an opportunity rather than a threat, we should view the increasing likelihood of Life Out There as exciting and intriguing. Bring on the Little Green Men, we'll see how good they are at drumming.

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