Date: May 11, 2011

Title: Planet Hunters

Podcasters: Chris Lintott and Meg Schwamb

Organization: Planet Hunters

Links: Planet Hunters, Zooniverse

Description: With NASA’s space-based Kepler mission, we have entered into a new era in the study of extrasolar planets (exoplanets). Planet Hunters is a Zooniverse citizen science project employing human pattern recognition to identify the signatures of transiting exoplanets in the Kepler data. Chris and Meg discuss Planet Hunters and early results from the project.

Bio: Chris and Meg are astronomers involved in Planet Hunters.

Chris Lintott is a researcher who is involved in a number of popular science projects aimed at bringing astronomical science to a wider audience. He is the co-presenter of Patrick Moore’s BBC series “The Sky at Night” and a co-author of the book Bang! – The Complete History of the Universe with Patrick Moore and Queen guitarist Brian May. He is one of the principal investigators for the Galaxy Zoo project, and runs Zooniverse projects, including Planet Hunters, which allow you to help scientists explore the Universe. Chris is now the Director of Citizen Science Initiatives at the Adler Planetarium in Chicago.

Meg Schwamb is National Science Foundation (NSF) Astronomy & Astrophysics Postdoctoral Fellow at Yale University’s Center for Astronomy and Astrophysics (YCAA). As part of the La Silla-QUEST KBO Survey (, she is searching the southern skies for the largest and brightest members of the Kuiper belt and beyond, and studying the orbital and physical characteristics of these new discoveries. Meg is project scientist for Planet Hunters, using the results from Planet Hunters classifications to study planet formation and evolution.

Sponsor: This episode of “365 Days of Astronomy” is sponsored by Astronomy.FM, broadcasting astronomy and science related programming over the internet 24 hours each day. Listen in at www.Astronomy.FM


CL: Hello, I’m Chris Lintott from the Adler Planetarium. With me is Meg Schwamb, a NSF fellow at Yale, but more importantly one of the astronomers behind the Planet Hunters project. So Meg, what is Planet Hunters all about?

MS: Planet Hunters is a citizen science project where we are looking through the Kepler public data set. So the Kepler spacecraft has been staring since 2009 at a same set of stars. Monitoring 150,000 of these stars, looking for the signature of extrasolar planets, and with Planet Hunters we are using citizen science to look through this data set to look at these stars to find drops in light due to an extrasolar planet moving in front of its parent star.

CL: So the idea is, if we are staring at the star or Kepler is staring at one of these stars and a planet is orbiting it, and it happens to get in between us and the star we happen to see a dip in light. Right that’s what we call a transit?

MS: Exactly. So the depth of the transit gives you an idea of the size of the planet because it’s the ratio of the size of the star and the size of the planet and the frequency of those dips tells you about the period of the planet or how far away it orbits from its parent star.

CL: So if aliens were doing this for our solar system, we’d see Mercury transit a few times a year, but you would have to wait a whole year to see Earth?

MS: Exactly. So for us to look for planets that are 1 AU, we will have to wait another year for a repeat in the dip in starlight.

CL: So you are asking citizen scientists, anyone with a computer essentially, to come and help you spot these transits, but that seems a bit bizarre. Why can’t you get a computer to do this job for you?

MS: Well the Kepler team is having computers do this. They have automated routines to search through the light curves from these 150,000 stars, but computers are only good at what you teach them to do, what you tell them to do. Where human beings are very good at picking out what is unique and interesting, and so our gamble is that human beings will be able to find transits that the automated routines won’t be able to find because there is so much stellar variability in short term variations in these light curves that has never been measured before because of the temporal resolution, how often we get a measurement of these stars. The only other star we have at this point to this precision is the Sun. We are seeing lots of stellar variability that we have never seen before. And so we think at Planet Hunters, the automated routines will fail at finding certain planets that human beings will be able to spot by looking at these light curves by eye.

CL: And so you are saying, if you stare at these stars every half an hour or so, which is what Kepler does, they just change from half an hour to half an hour and that gets confusing.

MS: Exactly, and there’s lots of this short term variability, in that you know again automated routines only do what you tell them to find, but human beings are very good at picking out the unique, and this has been show time and time again with Galaxy Zoo, another one of these citizen science projects you’re very familiar with. Again something like Hanny’s Voowerp or the green peas, these things have come out of someone saying hmm there is something strange here that an automated routine would fail to find.

CL: Yeah, so these are examples of weird stuff that people have picked up out of my Galaxy Zoo data. But back to Planet Hunters, this is essentially the gamble that your team and my programmers were going to make: Can you humans find planets that computers can’t. And then we launched in December after a pretty mad couple of months, if I remember correctly putting this together. How was launch day for you?

MS: Launch was overwhelming. We had this gamble of wondering, would people be interested in this project because it’s not pretty pictures of galaxies it’s actually seeing real data, points on a graph. It’s not very pretty to look at; it’s interesting to me but we weren’t sure if it was going to be interesting to others, and so the response has been overwhelming. We have over 22,000 users now that are looking through the data, and so I think my first feeling was being shocked at so many people being so interested in finding extrasolar planets and willing to spend their extra time looking through the data set for these transits.

CL: And pretty quickly, the results themselves were surprising as well.

MS: Absolutely, so at the end of January we wanted to get a preliminary search through the data set, and we came up with a list of planet candidates looking through the results from combining all the users who have looked at these light curves, and we came up with a set of 69 planet candidates that we think are stars that have transiting extrasolar planets. 47 of those are not on the Kepler team’s list of planet candidates or false positives, so things that look like planet transits but aren’t, or eclipsing binary lists – which are stars that are transiting in front of each other and show this dip that looks like a planet transit.

CL: So these are potentially independent discoveries?

MS: Yes, and so we are going through the process to further confirm these planets, and see if these planet candidates are real.

CL: I noticed you are being very careful and saying planet candidates. What do we have to do to turn these into planets? Why can’t I send emails to people now and say, “congratulations, you’ve discovered a planet” because you have this transit on the curve?

MS: It’s very hard to go from planet candidate to bona fide planet, and the Kepler team is having the same problem in that they have about 1,200 planets but only about 15 confirmed planets just to give an example of how hard it is to go from planet candidate to planet. So the reason is that there could be a background star like an eclipsing binary system, where again it is two stars where one is going in front of the other, that could be blended in with your star and so the signal is diluted and it looks like a planet candidate.

CL: Blended in because they happen to be in the same place on the sky, the same line of sight.
MS: Right. And it’s much fainter, so the only star that we see is the one we’re looking at, but behind it is the eclipsing system, and so the only way to really confirm these systems is with radial velocity measurements, where we actually measure the wobble of the star due to the transiting/orbiting body. So with that you can get an estimate of the mass of the system, which can confirm that if it’s a stellar mass, like an eclipsing binary of planetary mass, Jupiter sized or smaller. And so to do that, you need something like HIRES spectrograph on the Keck telescope, which is a 10 meter telescope on Mauna Kea, to observe these stars to try and measure this wobble to confirm that you see the object transiting is a planet and not a star or something else.

CL: So how are we doing? Any news for Planet Hunters candidates yet?

MS: We are actually following up our candidates. Debra Fischer who is the science principal investigator for Planet Hunters just last week was observing on the Keck telescope for 5, our top 5, planet candidates. She is getting spectroscopy of these systems to get a better sense of the stellar radius, so we can get a better idea of the size of the planet because the drop in light tells you about the ratio of the size of the star and the size of the planet. We are actively following up on candidates and applying for more time on the Keck telescopes and hopefully be able to get radial velocity measurements to rule out eclipsing binaries or a star as the transiting system.

CL: I guess one thing I should ask you, is how useful are the planet candidates because there are an awful lot of them out there and many of the Kepler stars are very faint, so many of these planet candidates may never become planets, they may just sit there as candidates. Is that still useful or is that a waste of decent solar systems?

MS: No, I mean Kepler is really designed to be a statistics mission really to get the statistics of planetary systems and the variety. Most of these candidates and most of the Planet Hunters candidates, we won’t be able to confirm with radial velocity measurements, but you can understand the frequency and variety of planetary systems just by the statistics of these planet candidates. That is something I’m actively working on Planet Hunters to look at the frequency of short period planets from our planet candidates. So we did a preliminary search through out data at then end of January to look through for planet candidates, and now we trying more sophisticated methods and algorithms to extract planet candidates from the all user’s classifications to come up with a list of planet candidates and look at the frequency of short period planets.

CL: So I know you still need help, there is new data up there right now. So how to people get involved if they fancy trying to discover a planet themselves?

MS: You can go to, and you can start looking at data right there and log in and see more of our interesting systems by logging in as zooniverse users. So you can go to and start right away.

CL: What is the one piece of advice that you could give to somebody if you could whisper in the ear of all these people listening to the podcast who are about to start looking for planets. What’s the one thing that you would say to them?

MS: Trust your instincts. If you think there is a transit it, mark it even if you’re not sure. There is no right or wrong answer, and so if you think there is a transit mark it.

CL: Good advice. Excellent. Thanks Meg.

MS. Yeah thank you very much

End of podcast:

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