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Exoplanets: Answering the Big Questions

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.


Comments on this entry are closed.

  • JohnHunt February 8, 2011, 12:05

    Most likely, the closest exoplanet will not be warm and wet. Yet the fact that is the closest and something which we would still like to get a look at means that this will likely be the target for our first true interstellar mission. At that point, the scientific question will not be so much, “Does it have evidence for life” but simply, “What interesting features does it have”. Think about all of the interesting things we have learned about the planets and moons in our solar system. Any rocky planet would be pretty interesting.

    Yet, at the time of launch of the first true interstellar craft, technology in other areas will be sufficiently advanced that people will logically wonder if the mission could do more. Whereas the nearest exoplanet may not be “habitable” it may be “inhabitable”. In 100 years, telescopic technology would probably tell us what resources in terms of atmosphere and ice caps the target planet had. In 100 years biotechnology, nanotechnology, robotics, and maybe AI will be sufficiently advanced to make people wonder about whether the mission should be in the business of using those technologies IF sub-craft could decelerate to a stop. If so, then it begs the question, “What else ouldcoul we do to make that exoplanet inhabitable even in a small Garden of Eden-style habitat.

  • Michael Gauthier February 8, 2011, 16:19

    Rather than speculate about what the closest exoplanet will be like, maybe we should be asking what the closest system will be like. Most of our own solar system may have seemed dead, dry, and desolate thirty years ago, but now we know better. Following this trend, and the recent discoveries of extrasolar systems, we should ask how common habitable or inhabitable systems are in the universe. We may find that the prevalence of rocky, earth-like worlds in circular, year-long orbits does not factor into the target priority of an interstellar mission nearly as much when considering the habitability of the system as a whole.

  • Ronald February 8, 2011, 17:18

    JohnHunt: “Yet the fact that it (i.e. the closest exoplanet) is the closest (…) means that this will likely be the target for our first true interstellar mission. ”

    I suppose that all depends on the future combination of two important factors: available technology and choice of exoplanets.
    If suitable (i.e. habitable or terraformable) exoplanets appear to be common, humankind will probably go for the best choice first, especially if it takes enormous investment to go there.
    If suitable exoplanets appear to be rare (and very distant) and/or technology has advanced so much that it is relatively cheap to go there, our first choice may indeed be (one of) the nearest.

    If, in the near future, Alpha Centauri A and B appear not to possess any rocky and potentially terraformable planets, the next nearest solar type candidates are ~11 (Epsilon Eridani) and ~12 (Tau Ceti) ly away. Neither candidate seems very ideal: Eps Eri is only marginally solar type (K2), Tau Ceti has very low metallicity, which has probably resulted in a failed planetary system (lots of dust and asteroids).
    The nearest solar type stars after that are over 16 ly away.

  • andy February 8, 2011, 19:16

    Looking again at Alpha Centauri in the light of the recent Kepler discoveries, one thing that definitely stands out is that the circumstellar discs would have been truncated fairly close to the ice-line. I’d guess this would make it less likely that any low-mass planets there are mini-Neptunes, so perhaps the relative lack of water there might actually be beneficial for forming terrestrial planets (contrary to what I have said previously regarding Alpha Centauri possibly being a poor candidate for habitability due to lack of water).

  • Mike February 8, 2011, 21:13

    I didn’t know the Allen Array was struggling for funding. Is Paul Allen able and willing to donate more money to complete his Array? The only way any SETI project can be accomplished at present is by private funding.
    One could hope that discoveries of Earth-size exoplanets in HZ orbits might increase public interest and public funding for SETI and other, more powerful astronomical projects. Private donations can’t provide the Giga-bucks needed for SKA, TPF, SIM etc.
    Kepler is doing a wonderful job and also showing that there is so much more to be explored in greater depth.

  • Phil February 8, 2011, 22:40

    Yesterday on arxiv there was an interesting paper that added another flavour to the exolife mix (although it would seem unlikely that intelligent life would be possible here)



  • JohnHunt February 9, 2011, 3:36

    > maybe we should be asking what the closest system will be like.

    I don’t know if it matters whether the closest exoplanet (or exomoon) is singular or part of a system. Given our technologic capabilities in a hundred or so years, I think that we could create a habitat on some pretty inhospitable bodies. Limited paraterraforming might also be within our technical abilities.

    Interestingly, we might be facing a situation where the closest potential target has a circumstellar disc which contains both asteroids and cometary material from which one could theoretically assemble everything needed for a rotating habitat. But I think that it might be well into the 22nd century before we could reliably assemble such a thing using automation.

    > I suppose that all depends on the future combination of two important factors: available technology and choice of exoplanets.

    Or even any technology which could be transmitted as software shortly before the craft arrives. Imagine a RepRap machine, 3 D printer, FGPA, chip fabricator, programmable cells, or the like. In that case we could apply 2200 technology to a craft launched in 2100. So, this is why I would be interested to see if any small sub-craft could be fully decelerated so that asteroidal or other material could be exploited for communications and manufacturing purposes.

    > Eps Eri is only marginally solar type (K2),

    The star system doesn’t need to be like ours in order to be inhabitable. If there are burnt out comets and various types of asteroids large enough to provide enough radiation shielding then theoretically you have the energy, matter, and artificial gravity that you need. What’s lacking is the right information and manufacturing ability at the molecular level. But if the sub-craft were radio programmed before decelleration and had even a rudimentary molecular manufacturing capability (e.g. RNA manufacturing) then future molecular engineers would be able to use that capability to produce ever larger scale tools. And certainly by 2200, Venter Inc would be able to program artificial cells and organ ink jet printing and ectogenesis will be a real possibility.

    My point is simply that a whole lot more than just scientific observations can be done in many star systems if you decelerate to stop, extrapolate from current technology, and humanity is still around to broadcast commands.

  • Martin J Sallberg February 9, 2011, 7:53

    And to that comes the possibility of gas giants having truly habitable moons and of theoretically too cold planets being warmed by greenhuse gas rich atmospheres. Travelling there is a problem, but there is good ideas on Space coonization wiki, where you also can add your own ideas.

  • Tarmen February 9, 2011, 22:05

    All those possible colonial strategies will be tried by some faction of mankind. And all those possible niches will be tried. We have the inborn drive. It only takes time. A century will pass. And then another will pass (without you and me). And then another century and another century and another and ..
    I foresee that waves of various human or human’ish migrants might ‘pulse’ out to the Outer Solar System, then the Oort Cloud and then the nearest stars and more. Scientific missions, political refugees, idealists, eccentrics driven by madness, entrepreneurs driven by greed, theocracies driven by their gods. And each pulse of mankind will chance doom. Some colonies might be overwhelmed and devolve into animals. But some happy few will find a niche and evolve beyond what they were. Someday, they’ll forget Earth.

  • Ronald February 12, 2011, 8:52

    JohnHunt: see my post of today under “Musings on Kepler’s Latest”, for my comment on suitability and marginality of star (spectral) types.