Maybe my favorite clever bit in Marvel’s Ultimates universe comes from Warren Ellis. He has Reed Richards “solve” the Fermi paradox. You know, how the Drake equation, no matter how you slide the numbers, predicts oodles and zillions of aliens out there. So…why haven’t we heard from anybody? Ultimate Reed Richard comes up with the answer—Galactus! He eats planets! The real world, on the other hand, is much more entertaining; we don’t have a pat deus ex machina as our answer, nor a super-genius to figure it out for us, so we have to actually do science. In the July issue of Scientific American, Michael Lemonick looks at what we know about exoplanets, and how we figured out what we know so far, in the article “The Dawn of Distant Skies.” The article has been retitled “Astronomers Search for Signs of Life in the Skies of Distant Exoplanets” for the online edition.
In 1996 Geoffrey Marcy said, after he and his partner found the second and third planets outside our own solar system, that “[p]lanets aren’t rare after all.” One of those vague little numbers in the Drake equation just got a little more solid, and to sort of everyone’s pleasant surprise, the answer to fp (stars with planets) is pretty big. Now, something like the Drake equation is a relatively simple model that largely exists for the sake of the conversation, not rigor, but the ease with which astronomers have been finding planets is heartening for those who think there might be someone—something—else out there. Even more uplifting, however, are the leaps and bounds scientists have made in the tools and methodology for recovering useful information from those exoplanets.
The techniques embraced by the recent crop of researchers focus on transits and eclipses; that is, if we can see the star, can we see when the planet orbiting the star is in front of it? Between us and the star? If we can find the minuscule dimming of the star while the exoplanet is in transit, astronomers can find out a bucketload of information. The amount it darkened lets you figure out a planet’s size, for one thing. You can deduce the mass of a planet from viewing the star’s Doppler shift—a small amount, but detectable—as it and the planet tug each other around their shared center of gravity. Boom, right there you’ve got size and mass and density. You can start making informed guesses from that, but when things really get tricky is when you start trying to figure out what is in the exoplanet’s atmosphere.
As the exoplanet passes in front of the face of the star, it shoots its light through the atmosphere, as you’d expect. Astronomers can use that light to do basic spectroscopy; every molecule has a different wavelength of light that it will absorb (sodium is, apparently, the easiest to spot) so you can deduce information that way. Moreover—as L. Drake Demming and David Charbonneau discovered simultaneously in one of those “how come so many interesting science theories are always discovered by two groups working independently?” moments—you can flip the process. Just as a planet is about to be eclipsed by its star, it shows part of its day side—and then it is swallowed up, blocked by the much more massive star. Comparing that (again, very tiny) spike in brightness with the now (slightly) dimmer star will get you a whole new set of calculations. At least, ever since the Spitzer Space Telescope went up.
So what kind of weird stuff have they found? How about hints that, sort of like Jupiter’s core in Arthur C. Clarke’s 2010, there are possible planets made of diamond? Insert YouTube clip of Good Will Hunting here: “how do you like those apples?” Nikku Madhusudhan’s work on the exoplanet WASP-12b suggests that it has an atmosphere with a ratio of 0.8 between carbon and oxygen. Now, WASP-12b is too big, but if the other planets condensed out of the same “soup” of elements, there would be other, smaller exoplanets made from the same stuff. A solid, Earth-sized planet could have entire continents made from diamond.
Or even better, a water world! GJ 1214b is 2.7 times the size of Earth and six times heavier, which is pretty close on a cosmic scale, and it isn’t even that far away, at 40 light years. The thing is, the density of the planet could come from an array of options. Maybe it is just a dense core with a huge puffy atmosphere. Maybe it is a sloshing bucket of water. If the latter, the obvious question is: could it support life? Jacob Bean at the University of Chicago is looking, but we don’t have answers. Yet. Which is the great thing about science. Brains are working on the problem, and new equipment is being made. In the next decade, new orbital and terrestrial telescopes will make this all easier, and ask new questions. Reed Richards might not be real, but that’s okay, we don’t need him.
Mordicai Knode thinks that when we find a habitable world in a binary star system that we need archeologist to dig back to “a long time ago…” to find fossil lightsabers. Oh wait, that would need to be in a far-away galaxy, too—never mind. You can follow him on Twitter and Tumblr.