Finding out whether this is the case means getting up close and personal. We’re doing that for Mars; however, the likes of Europa and Enceladus may have to wait a decade or four.
But maybe we don’t have to go anywhere. Instead, we might be able to sit here and wait for alien beings (of whatever form) to message us.
SETI is the Search for Extraterrestrial Intelligence, and its name tells you its story: it’s a group of astronomers looking for signs of intelligent life in space. They use various methods to look for advanced aliens, but the most promising one is to listen for any messages sent across the skies.
The basic SETI assumption is that aliens are out there and want to contact us. If that’s the case, there’s a good way they can signal us: radio waves. They’re the perfect medium: they’re cheap, easy to make, easy to encode with information, they travel across the whole galaxy unimpeded, and they move at the speed of light, the fastest thing we know. So SETI scours the skies looking for radio signals from ET.
They haven’t found anything yet, but as SETI astronomer Seth Shostak points out, we’ve just started looking. There’s a lot of galaxy and a lot of radio wave frequencies to sift through. But our technology gets better all the time, allowing for more sensitive searches. According to Shostak, if they’re out there and currently sending signals our way, we should have an answer one way or another in about 25 years given the way things are going.
I think SETI is a good idea. In a practical sense their engineers are advancing our radio technology and signal processing, and philosophically I think it’s interesting to listen for alien signals. But I do wonder about the basic assumption that aliens are out there and want to contact us – it’s a big leap, and based on our own human motivations. So while this is certainly worth the effort, it’s hard to know if it’ll pay off, and the 25-year deadline reflects that.
But I suspect another method may have the edge.
New world order
For a long time, we only knew of nine planets (including Pluto, though this was downgraded from its planet status five years ago), and only one that could support life. Then, in 1995, astronomers found the first planet to orbit another sun-like star. The planet wasn’t like ours at all – more massive than Jupiter, and orbiting so close to its parent star its temperature is over 1,000C. But it was a watershed moment. We finally knew that other planets exist.
Since then, Nasa’s Kepler space telescope, the European Space Agency’s Corot mission and ground-based instruments have found nearly 800 other planets, and that number grows every week. We know of enough planets orbiting other stars that we can actually start to extrapolate some numbers: it looks like approximately half of all stars in the galaxy have planets, and planets may in fact outnumber the 200 billion stars in the Milky Way.
We still don’t know how many of these worlds are like ours, but it seems like it’s a good bet the number is in the million, if not billions. We’re finding smaller and smaller planets all the time, and statistically speaking Earth-sized planets should be fairly common.
The big question is how many of these have life? We don’t know. But consider this: we have evidence that life on Earth started almost immediately after its surface was cool and stable enough to allow it. For three billion years that earthly life consisted of one-celled organisms, and it’s only relatively recently that these evolved into the type of multi-celled creatures that now inhabit every niche of this blue planet.