The biggest astronomy story of the past two decades is that the universe is studded with planets. Sweden's Nobel Prize committee clearly agrees, as they just handed their coveted physics award to Michel Mayor and Didier Queloz — two Swiss astronomers who were the first to find convincing evidence about a world in another normal stellar system. What they uncovered was a bulky planet orbiting 51 Pegasi, an otherwise unremarkable sunlike star about 50 light-years away.
Since that 1995 discovery, more than 4,100 additional exoplanets have been found. That's an impressive number, so it's fair to ask whether this new knowledge has changed the way we look for extraterrestrial life.
Few of these exoplanets are the kind you'd expect would cook up intelligent extraterrestrials. The universe boasts many, many second-string exoplanets: large waterlogged worlds, vaporous gas balls and objects that are simply too hot or too cold to be great places for biology.
Yet, preliminary estimates suggest that about 1 in 5 star systems contains a planet that is something like Earth. That adds up to tens of billions in our own Milky Way galaxy, and that doesn't count all the moons that might also incubate life.
Given all this newly uncovered cosmic real estate, shouldn't scientists involved in the search for extraterrestrial intelligence (SETI) be assiduously aiming their antennas its way? Wouldn't doing so better the odds that we'll trip upon some alien BFF?
Well, yes. And indeed, many of these exoplanet systems have been surveilled by SETI researchers. But the real influence of exoplanets on the hunt for E.T. is more subtle.
To understand why, let's briefly return to those golden days of yesteryear. When major SETI searches — ones that listened for signals from many hundreds of star systems — got underway in the early 1990s, we didn't know which might have planets. In fact, it was conceivable (but a poor bet) that none of them did. So SETI scientists preferentially pointed their instruments in the directions of sunlike stellar systems. After all, the sun was the only star we knew that (jokes aside) shone on intelligent beings.
This was a conservative strategy, and hard to fault — a bit like restricting your dining choices to familiar restaurant chains. Doing so confers a reasonable expectation of getting an edible meal, even if better fare might be had elsewhere.
The exoplanet discoveries have expanded the choices for researchers and eased their personal anxieties because they finally can be certain that planets are plentiful. As an example, consider a type of star that scientists had always excluded from the SETI club: red dwarfs. These bantam stars were considered unlikely to host many close-in planets — worlds that orbit near enough to their suns to receive sufficient energy to sustain life.
But exoplanet hunters have proven that assumption wrong. Several red dwarf stars have been found that are ringed by possibly habitable planets. And since 75 percent of all stars happen to be red dwarfs (only 8 percent are similar to the sun), this is like suddenly learning that there are 10 times as many restaurants in your neighborhood as you once thought. Your drive to dinner is shortened, and your menu options have increased.
The practical result of finding lots of planets has been to shift SETI efforts from looking at a certain type of star system to simply looking at the nearest ones. On average, the systems examined today are only half as far away as when only sunlike stars were examined. Any signals would be four times stronger and, of course, if we find someone at home, a back-and-forth conversation might be more practical.
Mayor and Queloz weren't looking for planets when they found one around 51 Peg, but they're being justly credited with paying attention to their data and realizing what it implied. Like many discoveries in science, theirs was accidental, but realizing its importance was not.
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