When Geoff Marcy (UC-Berkeley) got started in the exoplanet game, it was the result of an apparent dead-end. As Marcy tells Wired.com in a recent interview, he had been working as a post-doc at the Carnegie Institute of Washington, feeling ‘a little bit like an impostor’ and wondering whether a career in science hadn’t been a bad choice. But epiphanies happen in the strangest places. One afternoon he was taking a shower in Pasadena, and the rest is history:
“So I thought, what do I care about? I would love to know if there were other planets around other stars.
“This was a question that nobody was asking. It was 1983, and nobody was even talking about planets. Even our own solar system was considered boring at the time.
“So by the time I turned off the shower, I knew how I was going to end my career. I quickly realized that this was kind of a lucky moment. By knowing that I was a failure, I was free. I could just satisfy myself, and hunt for planets — even though it was a ridiculous thing to do. At that time, I hadn’t heard of anybody actively hunting for planets.”
Contrast that with this year’s AAS meeting in Seattle, where there were, in Marcy’s estimation, 500 talks and posters on extrasolar planets, and you realize how far the field has come. Consider that we have more than 500 identified planets now in play, with an additional 1235 candidates from the Kepler science team. Even at that, we’re just at the beginning. While we’re tracking Kepler worlds in a single patch of sky in Cygnus and Lyra, our knowledge of planets closer to home is vanishingly small.
Finding Nearby Planets
That’s why we’re going to need those ground-based follow-ups to the now canceled Space Interferometry Mission, to help us get a read on what’s orbiting the closer, brighter stars that would become the earliest targets for future interstellar probes. Writing about Project Icarus this morning, Ian Crawford (University of London) notes that we know about approximately 56 stars within 15 light years of the Sun, in 38 different stellar systems. Two of these stars — Epsilon Eridani and GJ 674 — are known to have planets, and two other stars — the red dwarfs GJ 876 at 15.3 light-years, and GJ 832 at 16.1 light-years — have planetary systems just beyond the 15 light year limit.
Project Icarus is tasked with designing an interstellar probe that could complete a mission to a nearby star — the 15 light year limit is seen as a maximum realistic range for such a craft, although Crawford notes that the actual target would presumably be much closer, assuming we could identify a good one. Epsilon Eridani is young, and its gas giant is in a highly eccentric orbit, not the sort of promising material we might wish if looking for a potentially habitable world. But the point is that as things stand now, we don’t have a complete inventory of what’s around Epsilon Eridani, nor do we know whether or not Centauri A and B have planets of their own.
The Search for Intelligence
For that matter, will the WISE mission find an interesting, nearby brown dwarf? Clearly, we have many questions to answer, which takes me back to Marcy. The exoplanet hunter believes there are two outstanding problems ahead of us. The first of them isn’t whether or not habitable, Earth-like planets exist, because most scientists now believe that somewhere in the vastness of the galaxy, such a planet would most certainly be found. The question is just how common such planets are. As Marcy says:
“Are they one in 100, one in 1000, one in a million? How far do we have to travel to find the nearest, lukewarm, rocky planet with an atmosphere?”
Kepler will help us with this one, but the second question is trickier. How common is intelligent life in the galaxy? We can learn a great deal about life’s formation by studying our own Solar System, and we may find exotic forms of single-celled life in places as distant as Titan or Enceladus, Europa or Mars. Hence the significance of the Europa Jupiter System Mission discussed in these pages yesterday. But even if we do find that life can form in unusual places, that still tells us little about whether or not intelligence is widespread.
For that we need SETI and tools like the Allen Telescope Array, which Marcy endorses, calling it ‘epochal’ and noting that the struggling observatory weighs in at a cost that is less than one percent of NASA’s budget in a single year. He’d like to see more willingness to fund research like this that would help us with the gigantic question of extraterrestrial intelligence, even as Kepler gives us some sense for the statistical distribution of worlds on which it is likely to occur. Fifty years of SETI have thus far produced no detections, but there are solid reasons for pushing on. For as we’ll see tomorrow, finding such a signal may be trickier than we once thought.