Artist’s impression of extrasolar planets. Credit: NASA

By Margaret Harris

Alan Boss is the kind of astronomer who sees the glass as not only full, but overflowing. Boss, of the Carnegie Institution for Science in Washington, US, told an AAAS audience that there could be up to 10^22^ Earthlike planets in the universe. Moreover, he argued that finding life on them is almost as inevitable as finding slime mould in a packed refrigerator left unplugged for two months. Maybe these extrasolar Earths don’t harbour life with two legs and a face, Boss said, but they should certainly be teeming with microbes and other simple organisms.

Avogadro’s number, 6.02 x 10^23^, is best known as the number of atoms in a mole, but in a fuzzier sense, it’s also a gold standard for mind-bogglingly large numbers. So 10^22^ Earthlike planets is really up there — and, as Boss noted, among astronomers an extra order of magnitude is nothing.

Perhaps I’m suffering from imagination failure, but a mole of Earths is hard for me to to get my head round. Judging from the mob of journalists who surrounded Boss after his talk, I wasn’t alone, and unfortunately someone from the New York Times led him away before I could do more than say hello.

However, if you’re interested in hearing more about Boss’ “crowded universe” hypothesis, fear not: he’s written a feature for next month’s print edition of Physics World on the same subject. In it, he talks about the search for extrasolar planets, and how new space telescopes will provide data to distinguish between a universe that is half full, half empty, or maybe even overflowing. So if you find the idea of 10^22^ extrasolar Earths intriguing, you know where to look.