It’s been about five years since I last wrote about the search for extrasolar planets–that is, planets orbiting other stars.
As I noted then, the idea that the universe is full of planets has been so firmly established in our minds by science fiction that it’s amazing to realize that we only found the first planet outside our solar system in the mid-‘90s..
Five years ago, the total had swelled to 98. And as of last weekend, with the announcement of the discovery of 28 new planets by the world’s largest team of planet-hunters, the total is 236.
That’s exciting enough. What’s even more exciting is that a planet discovered two years ago by the same team (made up of scientists from the U.S., Australia and England) has been observed crossing in front of its star–which has provided us with some details of its make-up.
Circling the star Gliese 436, the planet is slightly larger than Neptune and has a very short orbit, just 2.6 days. That means it’s very close–about 4.5 million kilometers–to its star.
That also means it’s very, very hot, so it most respects it’s not Earth-like at all. But in one very important way it is. When it passed in front of its star, Michael Gillon, a Belgian astronomer, was able to precisely pin down the planet’s mass, 22.4 Earth masses.
Geoffrey Marcy, professor of astronomy at the University of California in Berkeley and head of the California and Carnegie Planet Search team, puts it this way: “From the density of two grams per cubic centimeter–twice that of water–it must be 50 percent rock and about 50 percent water, with perhaps small amounts of hydrogen and helium. So this planet has…a rocky core surrounded by a significant amount of water.”
That’s not friendly-to-life liquid water, of course–it’s a form of “hot ice,” super-hot water compressed into solid form by tremendous pressures–but its presence suggests water is common in the galaxy.
And if that’s the case, then it’s quite likely that there are plenty of other planets–still awaiting discovery–where liquid water does exist, and life could happily thrive.
Because most planets are found by detecting “wobbles” in stars caused by the gravitational tug of orbiting planets, giant planets that orbit close to their stars are the easiest for us to find. We still can’t detect Earth-sized planets, but planet-detection techniques and technology are advancing all the time, and we may be able to within a few years.
After all, 15 years ago astronomers could only detect wobbles in a star of 10 meters per second. Now the limit is one meter per second. “We’re just getting to the point where, if we were observing our own solar system from afar, we should be seeing Jupiter,” Jason Wright of U.C. Berkeley says.
At least four of the systems where the new planets were found have more than one planet. So far 30 percent of the stars found with planets are known to have more than one, and that percentage will likely increase asddetection methods improve. And scientists are finding planets around many different types of stars, as well–not just stars like our sun but more massive stars and even in double-star systems.
In fact, more massive stars are even more likely to have large, Jupiter-sized planets in more distant orbits than sun-like stars are…and in fact are even more likely than stars like our sun to have planets of any kind.
Planets, it seems, are everywhere–they’re turning up around pretty much every sort of star, even pulsars, the dense stars left behind after supernova explosions.
“All of the studies are showing us that the frequency of planetary systems is larger than we would have guessed,” according to Alan Boss of the Carnegie Institution in Washington, D.C.
Lots of stars, lots of planets, lots of water…lots of life?
The jury’s still out, but I’d bet yes. Whether we’ll ever have a chance to travel out there and prove it, though…well, that’s a topic for another column.
Or a science fiction story.