Kepler: All systems go!


An artist's rendition of Kepler-11, a newly announced system of 6 confirmed transiting exoplanets that will be a laboratory for planet-formation theories for years to come. If these 6 worlds were somehow transplanted into our own solar system, all of them would lie within the orbit of Venus, and 5 would lie within the orbit of Mercury. How this "packed" planetary system was formed is a puzzle for astronomers. NASA/Tim Pyle

The Kepler teleconference ended a couple of hours ago. I tried my best to live-tweet salient details, so you can get your fill on my Twitter page. Here's the very compressed big picture: Kepler is working nearly flawlessly, and it's finding oodles of *candidate* transiting exoplanets, some of which appear to be rocky worlds orbiting in the habitable zones of their stars.

The Kepler team has announced more than 1200 new candidates.

Of those, 68 are approximately Earth-sized (equal to or less than 1.25 Earth radii). More than 50 candidates of all sizes are located in the habitable zone of their host stars, including 5 that are less than twice the size of Earth. The evidence suggests that smaller planets occur more frequently around smaller, cooler stars than hotter, larger stars, of which our Sun is one example. Nearly 15 percent of the stars with candidate planets harbor more than one candidate, suggesting that multi-planet systems are fairly common.

Much more work remains to be done, and indeed the follow-up observations required to confirm that all these candidates are actually planets will likely take many years. We still don't know if life exists elsewhere in the universe, but we've now taken another major step into the asymptotic frontier, and life's cosmic abundance appears more inevitable than it did yesterday.

This moment has been coming for a long, long time.

Most commentators will point to Kepler's immediate origins in a 1992 mission proposal called FRESIP from Kepler's eventual Principal Investigator, William Borucki. But I prefer to trace the defining moment back forty years more, in the overlooked musings of a brilliant Russian-American astronomer, Otto Struve.

In this paper, first published in The Observatory in 1952, Struve lays out the basic case for hunting for planets using both high-precision radial-velocity spectroscopy as well as transit photometry. He was a remarkably prescient man, and his story is worth telling, but that will be for another time. Suffice to say, I think Struve deserves far more credit than he has received for his early contributions to the wildly successful modern era of planet-hunting.

Of course, the trail goes back further still. Some 2,500 years ago, in Ionian Greece, a man named Leucippus, of the town of Miletus, first theorized that everything in the universe was made of tiny, indivisible atoms.

His disciple, Democritus, extended these ideas to state that endless configurations of atoms and void created infinite worlds that exist apart from our own, and that the Milky Way's soft glow emerges from countless faraway suns. Two centuries later, the philosopher Epicurus best summarized these ideas in a letter to a certain Herodotus (not to be confused with the historian of the same name): "There are infinite worlds both like and unlike this world of ours ... We must believe that in all worlds there are living creatures and plants and other things we see in this world."

It's not a stretch to say that, with today's announcement, the Kepler team has, in one swift stroke, made more progress toward solving this ancient mystery than has been made in the entirety of previous human history on Earth.

Think about that, and then realize that the most exciting steps—confirming these planets, finding ones even more Earth-like around nearby stars, and studying them for signs of life—still lie in our future. With any luck, and a hefty helping of public engagement, these things will happen before you, me, and everyone we know are only memories like Struve and Democritus.

Read More: Here's a nice round-up of coverage from Emily Lakdawalla of the Planetary Society. Nature has an excellent overview of the new discoveries, including a smashing Kepler feature story by Eugenie Samuel Reich, and an accompanying piece from yours truly discussing cost-effective technical and technological developments that are poised to deliver potentially habitable worlds for prices even a rabid deficit-hawk could love. I'll probably discuss some of those developments in more detail in coming blog posts.



  1. How could it be that six planets can be formed and/or maintained at an orbit smaller than that of Jupiter (Kepler 11)? Does this likely impact the nebular hypothesis, or are there other models of planet formation that might be needed?

    Speculation, please.

    1. Well, if they have weird and disparate compositions, they could conceivably be captures, but that’s highly unlikely. They could have just formed there. I’d day the most likely answer is inward migration from gravitationally interacting with each other.

    2. One of the big findings of modern planet formation research is just how much planets move around during formation. There are several well-studied migration mechanisms: Actually, one of the big problems is getting planets to *stop* moving around.

      I am currently studying planetesimal-driven migration as it may have applied to the formation of rocky planets. It’s likely that the Kepler-11 system experienced some form of planet migration, although our understanding of all the physics involved is still relatively incomplete. More observations like Kepler’s will help inform and constrain models, as will future observations. For instance, the ALMA observatory ( ) will give us lots of information on the structure of planet-formation disks around young stars at very high resolution. This is indeed a very exciting time to be involved in this kind or research.

    1. “The thing that hath been, it is that which shall be; and that which is done is that which shall be done: and there is no new thing under the sun.” Ecclesiastics 1:9

  2. This is seriously one of the coolest things I’ve heard in a very long time. Remember a few short years ago when there wasn’t direct proof of any exoplanets?

  3. Space telescopes = awesome!

    But I’ve got a copy of Lucretius here, and I don’t think the atoms he’s talking about bear much resemblance to the atoms of Rutherford and Bohr. The ancestry is there, only about as tenous as Clerk Maxwell’s relationship to Unix daemons if you ask me.

  4. Any word on which stars those five Earth-range planets in habitable zones are orbiting? Would be interesting to know if they’re all smaller stars than the Sun (smaller stars are actually more long-lived, right?), and for sci-fi fantasy purposes would also be interesting to know how far away they are from us.

    1. Hi Jesse,

      If I’m interpreting things correctly, all of the five HZ-orbiting *candidates* that are estimated to be twice the size of Earth or smaller are orbiting stars smaller than the Sun. Otherwise, we wouldn’t be seeing them yet in the data. Generally speaking, the Kepler team wants three transits of an object to be sure it’s legit. For a star like our Sun, something at Earth’s location in the habitable zone orbits with a period of a year. So we won’t be seeing any of those puppies til 2012, it seems. Smaller stars are cooler and less radiant, so their habitable zones are closer in, meaning that objects there have faster orbits. So they make three circuits faster than HZ-planets around larger, hotter stars.

      All the stars are very far away, and very dim too. IIRC, the stars for the two most promising candidates each have an apparent magnitude of 12-something, which is pretty faint.

  5. Some of these planets have very short rotations around there star i wonder what there night sky looks like? While i know the rotation of a planet is one way the stars move across the sky the rotaion around the star is another.

    Would streaks of light in the sky be considered stars if anyone was to view them?

  6. Don’t forget Giordano Bruno when discussing the history of human thinking about atoms and infinite space.

  7. Greeks weren’t the first to theorize atoms and other planets. This was written in Srimad Bhavatam and Mahabarata written by Sage Vyasadeva in ancient India beore the greeks. Check out Hindu Cosmology, they already know all of this.

    1. Yeah, but again, the atoms of the ancient Hindus didn’t bear a very strong resemblance to those of Rutherford and Bohr. The ancient Greek and ancient Indian atomic theories were impressively brilliant from a philosophical and logical perspective, but really have more to do with epistemology and theology than with physics.

      When you are arguing that wood must be a compound substance because it contains atoms of fire that can be liberated by ignition (or that meat is a compound substance because it spontaneously generates maggots) you are pretty far away from valence shell calculations. It’s still impressive, but it does not subtract any primacy from more recent atomic theorists.

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