Two exoplanets discovered by "citizen scientists"

By Phil Plait | September 22, 2011 9:57 am

Two new planets orbiting other stars have recently been discovered using NASA’s orbiting Kepler telescope. And while every new planet discovery is pretty amazing, normally two more add to the hundreds already confirmed wouldn’t really be newsworthy. However, these two weren’t discovered by professional astronomers! They were found by members of the Planet Hunters "citizen scientists" team; regular folks who have volunteered to sift through data returned by the observatory in hopes of finding far-flung worlds.

One of the planets found orbits its star with a period of just under 10 days, and the other orbits a second star in just under 50 days. Both are much more massive than Earth; the first is 2.65 times and the second over 8 times our diameter. The relatively lower mass means the first one might be rocky (as opposed to a gas giant) but the short period means it’s hot, far hotter than Earth.

Both planets transit their stars as seen from Earth. In other words, they pass directly in front of their stars from our point of view, blocking the light a wee bit. This drop can be measured, and the planet detected. By knowing how big the star is (a dwarf, a giant, whatever) the period of the planet can be found, and the size of the planet can be determined by how much light is blocked, too.

The Kepler observatory is staring at about 100,000 stars all the time to look for these mini-eclipses, and astronomers use a fleet of software to automatically tag suspicious changes in starlight. But it’s pretty hard to look through all the potential planet data, and that’s why Planet Hunters was set up: let people go through the data themselves, using their keen eyes and powerful brains to look for anything that might be a planet.

And it worked! The two planets discovered were just announced in a paper led by the Kepler team (PDF). Here’s a plot showing one of the transits:

That’s the data for KIC 10905746, the 2.65 Earth-mass planet with the 10 day orbital period. The top half shows the brightness as measured by Kepler; the star is a variable star which means it changes its own intrinsic brightness with a period of every few days. That makes this a difficult target! The red lines mark the transits spotted by the planet hunters; you can see where the brightness dips more than usual. Hard to see, aren’t they? But once you get the period of the planet, you can then "fold" the data, cutting it up into time intervals based on that period. Observations that were taken at different times — but show the planet in the same position relative to the star (for example, every time the planet is right in the middle of the transit) — can then be added together, cleaning up the noise. That’s in the bottom half, which shows all the transits stacked up (and with the star’s own changes mathematically removed). The dimming of the star’s light is much more clear — the red line is the best fit to the event. But note the scale: the planet only blocks 0.2% of the star’s light! It’s pretty amazing that we can see it at all.

Remarkably, both stars in this case were flagged as potential planet-bearers by the software, but also removed from the list to make followup observations by the same code! In the case of the star shown, it’s because the star was thought to be a giant near the end of its life, making followup observations and analysis too difficult. However, the human brain is pretty good at his sort of thing, and several people on the Planet Hunters site picked out the planetary transit.

I’ll note that the planet orbiting the binary star announced last week was also spotted by a Planet Hunter! The Kepler team had already spotted it as well, so they get the credit, but still. It doesn’t take a professional to find even the really weird planets out there.

Pretty cool, and good indicator that this citizen scientist project has a bright (or very slightly dimmed, I suppose) future ahead of it. And you can still participate! All you have to do is go to the Planet Hunters website, sign up, and get cracking. Who knows? Maybe you’ll find another world…

… and I have to wonder. An Earth-like planet orbiting a Sun-like star will have a very weak transit. A computer would have a very hard time picking that out of the data, but we humans are pattern-finding machines. Will the first exoEarth be found by a professional astronomer, or instead by some science enthusiast who decided one day to check out this Planet Hunters thing…?

Image credit: transit art: ESO/L. Calçada


Related posts:

- YOU can find extrasolar planets
- Astronomers discover a wretched hive of scum and villainy
- 50 new worlds join the exoplanet list
- Kepler finds a mini-solar system

CATEGORIZED UNDER: Astronomy, Cool stuff

Comments (18)

  1. I’m in that paper as one of the citizen scientists, and I can’t overstate how exciting it is for me. It’s really such a small thing, but being a tiny part of the team makes me feel directly connected to the incredible, ongoing journey of scientific discovery.

  2. Thanks Phil! Just a note to say although many of the coauthors are from the Kepler team, it’s led by our slightly independent planet hunters team from Yale, Oxford and Adler.

  3. Congratulations Squidocto! :D You are living a fantasy/dream of mine.

    And for some even more cool perspective on these discoveries, here is a StackExchange Question and Answer regarding the chances that a system will actually be edge on enough for us to measure these dips. As I say in the answer that I gave to that question, Kepler has been up there for a short while, and has a possible list of nearly 2000 planets just looking at about 150,000 stars for only a couple of years! So if only 1% statistically transit, that would mean that just randomly 1500 systems would have the correct orientation (given the results to date, that makes sense). And given that about 7500 stars were eliminated from consideration due to being variable of one sort or another… I think it would be pretty safe to say that pretty much every star out there has at least some sort of planetary body around it.

  4. Beau

    I sometimes log into Planet Hunters just to give it a go in the hopes that I could actually help in discovering a new planet. I’m glad some people actually did.

    Sifting through all that data gets a bit tiring though.

  5. jimthompson

    Nice catch by the amateur planet hunters, but there’s a mistake in the post: “it’s because the star was thought to be a giant near the end of its life, making followup observations and analysis too difficult.” is incorrect. The reason giants are avoided is because transits of them, of the depth typical of planets, would be made by STARS, not planets. While Kepler has found over a thousand eclipsing binaries and they are being well studied, such an eclipsing system counts as a “false positive” when searching for planetary transits.

  6. jimthompson

    While this is a great and exciting thing for the Planet Hunters, another, less optimistic way to look at it is as a failure of the Kepler team’s processing pipeline. Both these objects were initially flagged by that software, at high signal to noise, but, for various reasons (some as yet unexplained) these objects were later dropped and not further analyzed. The Planet Hunters had a high false positive rate of at least 60%, though this was not unexpected. This suggests that perhaps a more efficient way of combing the database is to put human eyeballs on THAT list of stars: those initially flagged but later dropped by the Kepler processing pipeline. Certainly that would have easily detected the planet with the near 50 day orbit. One has to suspect that such a plan might already be in use, which would make any future discoveries by the Planet Hunters, unfortunately, considerably less likely.

  7. From the linked paper it sounds like they just examined the top 10 candidates of the top 45. Sounds like it would be worthwhile to look at the remaining 35.

  8. Ron Richter

    The picture is a great example of chromostereopsis!

    Stare at it for a second or two

  9. CoffeeCupContrails

    Note to amateur self: Gaps in Kepler data most likely means (just checked: yes it is) end of some observation period. That’s not a huge planet with a weird orbit. Now get back to work – that wheel won’t spin itself.

  10. mig500

    Another citizen scientist here. I have flaged the 2 planets :) )) So Happy!!!

  11. Kim

    Food for imagination: inhabitants of those planets can detect the Earth as well, as we are on the same plane. Hopefully, they’ll be glad to find us as we are to find them.

  12. Joseph G

    @Squidocto: Congratulations!!
    I tried my hand at that and couldn’t make heads or tails of anything I saw.I’d never have seen te pattern in that first graph in a million years :)

  13. Eimear

    I also tagged a planet. Very satisfying felling if I must say so, I would encourage more people to spend some time on the planet hunter site. Its not just finding planets that are fun, there are some really interesting light curves to be seen.

  14. Messier Tidy Upper

    @1. Squidocto, (#10.) mig500 & ^ Eimear & the others involved in discovering new found worlds :

    Congratulations! :-)

    Well done! :-D

    [Raises beer in celebration salute.] 8)

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