Panspermia and the Drake Equation: Looking Good

One by one, the empty boxes in the Drake Equation are being filled in with actual numbers, and it's looking good. So good that Yuri Milner is spending $100 million of his own money over the next ten years to fund the search for non-human civilisations orbiting other stars. But it's a pity that the Philae lander from the European Space Agency's Rosetta mission didn't have more time to look for life on Comet 67P/Churyumov-Gerasimenko.

Yuri Milner is a Silicon Valley billionaire who was working on a PhD in theoretical physics at the Russian Academy of Sciences before he moved to the United States and got rich. His money will buy thousands of hours of radio-telescope time each year to look for radio transmissions from other star systems.

This represents at least a tenfold increase in the amount of work being done on finding intelligent life elsewhere in the galaxy, and Yuri Milner is no fool. Why does he think it's worth spending this money now?

Probably because the Drake Equation is finally coming into its own. It has seven terms, and American astronomer Frank Drake could not give a value to any of them when he first wrote it in 1961. It was just a formula that would let us estimate the number of civilisations in the Milky Way galaxy when the relevant data eventually became available.

Using the data acquired in the past twenty years, NASA now estimates that there are 144 billion habitable planets in our galaxy. Not all of them will harbour life, of course, but that is a very encouraging number. 

Other questions remain, however. How many "habitable" planets will actually have life on them? On how many of those planets will an intelligent species appear? How many of those intelligent species will build civilisations that use...