William Borucki’s talk about the early Kepler findings on Monday created the biggest spike in traffic I’ve ever seen on Centauri Dreams, enough to blow through our memory allocation and crash the site for about twenty minutes. I had to reboot the server and up the memory to get back online, a tribute to the interest Kepler continues to generate in our community. I’m also getting plenty of comments from people at the American Astronomical Society meeting in Washington. If you use Twitter, use the hashtag #aas to join the ongoing stream of short updates.
Right now Scott Gaudi’s talk on Tuesday is generating the biggest buzz. Gaudi (Ohio State) reported on a gravitational microlensing effort called MicroFUN (Microlensing Follow-Up Network), one we’ve previously discussed in these pages. The method is well understood: One star occults another as seen from Earth. The light of the more distant star is magnified by the nearer one, and any planets around the lensing star momentarily boost the magnification as well. You find planets this way, though they’re not planets likely to be observed again because of the nature of the method.
I love this Gaudi quote from the talk: “Planetary microlensing basically is looking for planets you can’t see around stars you can’t see.”
Gaudi’s team has concluded that about fifteen percent of the stars in the galaxy are orbited by planetary systems like our own, meaning they have several gas giants in the outer part of the solar system. That fifteen percent is telling. “Solar systems like our own are not rare,” says Gaudi, “but we’re not in a majority, either.” Microlensing is useful for this kind of study because the method does a good job at picking up giant planets far from their primary star, a more difficult task with Doppler methods.
Working with colleague Andrew Gould, Gaudi used four years of MicroFUN data and folded in a statistical analysis based on ‘robust assumptions’ and the earlier work of both men. It turns out that MicroFUN in that period of time has revealed precisely one solar system with two gas giants in roughly the configuration of Jupiter and Saturn. Statistically, if every star had a solar system like ours, we should have found about six such systems by now. The slow discovery rate implies only a small number of systems have our configuration, no more than about fifteen percent. Says Gaudi:
“While it is true that this initial determination is based on just one solar system and our final number could change a lot, this study shows that we can begin to make this measurement with the experiments we are doing today.”
And as Gould notes, given the number of stars in the galaxy, even narrowing the odds down to fifteen percent leaves several hundred million systems that could resemble ours. Nor should we assume that a system necessarily has to mimic our own for life to develop within it. Nonetheless, this is an intriguing result that reinforces our sense that extrasolar planetary systems come in a surprising variety, one we learn more about with every new detection.