Revisiting the Drake Equation

Posted on February 13, 2012


Planet Hunting

If you are one of the many, many people out there who has sat down with the Drake Equation to try and work out just how many other species there may be out there in the galaxy that we could talk to if only we could get in touch somehow, then there is some new work that may make you do it all over again.

So far, we have found several hundred extrasolar planets spinning around stars in our near vicinity. Near, of course, is very much a relative term in a galaxy spanning a hundred thousand light years and is only a tiny sample when compared to all the billions of stars spinning around with us in our single galaxy. but are the discoveries we have made representative or are there perhaps even more planets around more stars out there than we have so ar found indication of?

English: Extrasolar planets discovered by year...

Planets found by microlensing

To find out if planets are really rare or if they are just hard to find, Arnaud Cassan of the Pierre and Marie Curie University in Paris and their collegues have turned from our existing methods to look at gravitational microlensing. The techniques looks for the focussing effect of planets on the light from their star and an be used to reveal planets as far as 20,000 light years from Earth – greatly extending the range at which extrasolar planet could be discovered.

Examining six years worth of data from microlensing events, they have estimated that extrasolar planets are actually the rule rather than the exception and that each star hosts an average of 1.6 planets. Of course, using microlensing does not pass on as much information about the planets as our existing methods so there is much less that can be deduced about the planets other than their presence, but this is a huge increase in the existing estimate of planets in the galaxy.

The scene from Ep IV: A New Hope showing the d...

Meanwhile, Wiliam Welsh of San Diego State University has been looking at stars observed by NASA’s Kepler satellite and have so far investigated 750 of them. They estimate that several million planets in the galaxy orbit not one but two stars, much like Tatooine in the Star Wars films and books.

It seems that the more we look the more we find and Drake Equation fans out there shoudl be slotting in a figure of perhaps 150 billion to 300 billion planets in the galaxy. That would vastly increase the chances of there being people out there we could talk to, but is still not big enough to place themwithin anything resembling a practicable reacheven for light-speed communications.

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