There's a new piece on my Guardian online blog, Across the Universe:

How many other inhabited planets are there? It's a question that fascinates scientists and lay people alike. A new equation may help weigh up the possibility

Many of us have glanced upwards at the stars and wondered whether there is other life out there somewhere. Few, however, have then tried to write down an equation to express the probability in numbers.

Sara Seager of the Massachusetts Institute of Technology has done just that. Her equation collects together all the factors that could determine how many planets with detectable signs of life may be discovered in the coming years.

The factors include the number of stars that will be observed, the fraction of those stars with habitable planets, and the fraction of those planets that can be observed. First presented at a conference earlier this year, the equation is written as N = N*FQFHZFOFLFS. It was published yesterday in the online Astrobiology magazine...

Read the whole piece here.