Question: How likely do you think it is that we would come in contact with other life in space? And so, when do you think it will happen?

Sara Imari Walker answered on 20 Jun 2011:

Hi again cai! Really cool question. There are several difficulties with trying to pin down a precise timeframe. The first is that we just don’t know if there is other life out there (I along with many other scientists think there is). The second is that we don’t know where we will find it, or what form it will take. Right now we are searching for extraterrestrial life on two fronts: searching for alien microbial life in our solar system, and searching for signs of extraterrestrial intelligence (more along the lines of movie aliens than the first option) by searching radio emission from other parts of the galaxy.

We focus on microbes in our own solar system because microbial life is likely to be the most common form of life in the universe. Single-celled organisms are by far the dominant form of life on earth – with upwards of 1 billion bacteria in a single teaspoon of dirt from your backyard. Also they live EVERYWHERE, from the hydrothermal vents on the ocean floor, to extreme cold of the Arctic, to deep underground. So, if alien life exists in our solar system it is probably microbial. If we get enough space missions up there – like sending probes to Mars, Europa, or Titan we may find it in the coming decades. But it depends on how hard we look!

It has become pretty clear we don’t have intelligent aliens in our solar system. But we can comb the skies looking for signs of advanced civilization. SETI (search for extraterrestrial intelligence) has been looking for advanced life for about 50 years. They haven’t found any yet – but their are literally billions of stars out there, that’s a lot of places to look!! We could find a signal tomorrow or not for several thousand years, its a mystery!

It’s really fun to think about!