Where will we be in the exoplanet hunt by the year 2020? A few of my own guesses would take this form: We should, within even the next year or two, have detected a terrestrial world in a truly unambiguous position within the habitable zone of a star. That star will doubtless be a red dwarf, like Gliese 581, but we can hope for a result that doesn’t lend itself to so many conflicting interpretations. The detection method will surely be planetary transit, but even by 2020 we may not know if life exists there.
It’s also easy to surmise that by 2020 we’ll have a terrestrial-class world located within a stellar system not completely dissimilar to our own; i.e., one involving a star much like the Sun, orbited by a rocky world in the habitable zone. We can hope that by 2020 the tools will have been put in place to do spectroscopic observations of the planetary atmospheres involved in small rocky worlds, though so much depends on budgets and the needed tuning up of exquisitely sensitive technologies.
I have a number of other guesses that could come into play, but I’m already second-guessing myself. And now I’m drawn up short by Drake Deming (NASA GSFC), who reminded the recent conference at the Space Telescope Science Institute that going back thirteen years instead of forward, we would remember that only the pulsar planets were known to us at the time. Planets around pulsars were incredibly exciting back then, and we know now that PSR B1257+12, the first pulsar involved, actually has at least three planets instead of the two first discovered.
But one thing pulsar planets are not and that is likely homes to anything like life as we know it. Alien to the point of absurdity, they basically proved something about the likelihood of planets being found elsewhere, but who would have guessed from them that we would find such things as ‘hot Jupiters’ or triple star systems with planets of their own? No, making guesses in a field expanding this rapidly is a dangerous game, one I’m nonetheless glad that Deming and the other scientists at this meeting were willing to play.
The conference, which ended on November 15, was titled “Astrophysics 2020: Large Space Missions Beyond the Next Decade.” Its goal was to look at the groundwork that will be laid by emerging technologies in that time. Ponder: The Ares V heavy launch vehicle means that some of the barriers to putting massive astronomical observatories into space will disappear. Moreover, we’re getting better at robotics, leading ultimately to construction and servicing jobs in space that would previously have been impossible. All this was fodder for conference discussion.
I couldn’t be at the STScI conference, but I’m listening to Dr. Deming’s presentation right now as he discusses the possibilities emerging in the field of transit observations. The entire conference is now available, thirty presentations and panel discussions online in PowerPoint as well as low and high-bandwidth streaming or downloadable video. Need I point out what an educational opportunity webcasts like this provide? As more and more conferences take STScI’s lead, the ability for those unable to attend to learn from the conference experience will become the kind of resource we only used to dream about.
I thank STScI’s Ian Jordan for passing along the much appreciated link to these webcasts, thus allowing me to confound my family by watching presentations all weekend. Fortunately, my wife is a patient woman…
And so back to Drake Deming, who is explaining in a video window on my desktop that direct detection of planets will be occurring in the not so distant future — direct detection means separating planetary photons from stellar photons, no easy task but increasingly feasible nonetheless. But even before that goal is reached, there’s a great deal we can discover about planetary atmospheres. Dr. Deming is moving on to discuss how transits can be used to identify habitable planets around M dwarfs, so he’s lighting up practically every synapse I have, obsessed as I am with the M dwarf planetary question.
We have already identified 20 known transiting exoplanets and the discovery rate is accelerating — twelve were announced just this year. As Dr. Deming discusses a temperature inversion in the atmosphere of HD 209458b, I’m reminded that even now we are making the kind of observations of planetary atmospheres (and indeed, constructing the crudest of maps based on temperature data from secondary eclipses as the planet passes behind the star) that no one thought we could do just a few years ago. The ‘hot Neptune’ GJ 436b likewise shows how transits can reveal surface temperatures.
You can see why the lowest mass M dwarfs are so attractive as we shoot for still smaller planets: Here the habitable zone lies close to the star, meaning short orbital periods and a higher probability of transits. And the small size of the star means that rocky planets can more easily be detected (Dr. Deming covers this in detail). M dwarfs also outnumber stars like the Sun by ten to one. “The nearest habitable planet to Earth,” Deming is saying as I write, “probably orbits an M dwarf, just because there are so many of them.”
You’ll want to watch Dr. Deming’s presentation to learn about the MEarth Project (Mt. Hopkins, AZ), using eight 16-inch telescopes to survey the 2000 nearest M dwarfs for rocky planets in their habitable zones, looking for planets that will be good candidates for spectroscopic follow-up (not with Spitzer but via the James Webb Space Telescope) to search for atmospheric biomarkers. We could be looking at extremely interesting data from the atmospheres of such planets as early as 2015.
Does that gibe with your own predictions? Those interested in all branches of astronomy and astrophysics will want to work through all these presentations to see what’s ahead as we put the latest hardware to work and continue to refine our techniques. Well done to the conference presenters for making this treasure trove available!