Amateur planet hunters find a world with a four star rating

By Phil Plait | October 15, 2012 9:30 am

A new exoplanet – a planet outside our own solar system – has been found, and it’s pretty cool for two reasons: it was found by amateur planet hunters, and it’s in a four-star system!

OK, first, the planet: called PH-1, it’s bigger than Earth, about six times our radius, or about half the diameter of Jupiter. The mass isn’t well known, but may be as high as 170 times our own mass, though far more likely it’s closer to 20 – 50 times our mass. That makes it closer physically to Uranus and Saturn than Earth, so it’s likely a gas giant. It’s also hot, with a probable cloud-top temperature of 400+ Celsius (800+° F). Even if it has Earth-sized moons they’re likely to be too hot to be hospitable. And since it’s 5000 light years away, we’re not headed there any time soon, anyway.

But the more interesting thing about this planet is its host stars: PJK-1 orbits a binary star, two stars that orbit each other (like Tatooine, if you like). Six other planets are known to orbit binary stars, but PH-1 is even cooler: the binary star is itself orbited by another binary pair much farther out, making it the first planet found in a four-star system.

So we have two stars orbiting each other, orbited by a planet, and also orbited by two other stars which orbit each other. Yegads.

But it gets better yet. This planet was not found by professional astronomers! It was discovered by two amateurs who participate in the Planet Hunters program. This project was started by astronomers using the orbiting Kepler Observatory, designed to stare at 100,000 stars and look for dips in light from them as any potential planets orbiting them block their light. These transits show up in graphs of the stars’ brightnesses, and actually our human eyes and brain are pretty good at picking them out. Planet Hunters puts Kepler data online for anyone to go in and poke around.

The two citizen scientists, Kian Jek and Robert Gagliano, are listed as authors on the scientific paper recently published. I love this: the digital nature of these data make it far, far easier to analyze the science than it was in the past, and also easier to get the data out to people. Because of this, we have an explosive growth in these kinds of projects. Planet Hunters is great, but then so is Galaxy Zoo, Moon Mappers, Ice Hunters, and so many others. You can find several of these collected at the CosmoQuest website.

And a word about this new planet; this isn’t the first planet found by Planet Hunters, but it’s the first ever found in a quaternary star system. In the image here, the central binary is the big blob in the middle, and the second pair the elongated double-blob to the lower left. The planet is far too close to the middle stars to be seen here – its orbit is smaller than Earth’s around the Sun, far smaller than a pixel in this image at that distance.

The central binary is made up of a bluish star hotter and brighter than the Sun, and one that’s cooler, fainter, and redder. The second binary is made of one star much like the Sun, and another dinky red one. Their distance from the planet – about 150 billion kilometers – means they’d both still be very bright, with the brighter of the two almost as bright as the full Moon as seen from Earth. What a sight that would be! The second star would be hard to pick out in the glare of the other, but with binoculars you could spot it.

Not that anyone could, since the planet is hot enough to melt tin and assuming it had a solid surface to start with. Still though, it’s not hard to imagine a smaller planet orbiting that binary farther out, in a cooler, more life-friendly position. And we know such a planet exists; Kepler recently revealed a planet orbiting a binary star at the right spot to have liquid water as well. Like PH-1, that planet is probably a gas giant, but it might have big moons…

And this shows us once again that nature just loves to make planets, even ones in really weird places that at first may seem inhospitable for planet formation. But there it is.

Every time we find a strange planet like this, it fills me with hope that the ultimate goal of this work is close: finding an Earth-sized planet in the habitable zone of another star. We’re getting closer every day to that announcement, I think. In fact, I strongly suspect that planet is already sitting in the Kepler data, faint and hard to tease out, but just waiting to be found.

Go sign up for Planet Hunters. Maybe you’ll be the one to find it.

Image credits: Haven Giguere/Yale; Keck Observatory/Megan E. Schwamb et al.

Related Posts:

- Two exoplanets discovered by "citizen scientists"
- YOU can find extrasolar planets
- Astronomers discover a wretched hive of scum and villainy (and the followup, Exoplanet news Part 4: More wretched hives of scum and villany)
- Kepler finds a planet in a binary star’s habitable zone

Comments (46)

  1. Jess Tauber

    Maybe 4 stars, but likely not a decent hotel in the entire system…

  2. Brad

    Awesome!! I love that citizen scienctists are responsible for this! It would be amazing to see this spectacle in person.

    Also, I wanted to thank you for listing organizations and sites where we can get involved.

    Lastly, I think there might be something off with your statement about the second binary pair being 150B km away from PH-1. In our solar system, Pluto is only ~5.7B km from the sun and the sun is already much dimmer than the description of these stars for PH-1… Given the stars in this pair are sunlike and a red dwarf how would this be possible?

    Thanks again,

  3. Frost Bite

    “Few have witnessed what you’re about to see”
    I love Galaxy Zoo! The chance to see and classify objects in the universe that are soooo beautiful is unreal, so many different galactic structures that you could never imaging in your wildest dreams. A tip of the hat to those that have allowed us dreamers without the higher level education to take part in what those like Phil spent many years and dedication to educate them self and pass that precious knowledge on to us, thank you.

  4. gameshowhost

    quaternary is a great word

    quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary quaternary

    //couldn’t help it

  5. Chris A.

    @Brad (#2):

    ” In our solar system, Pluto is only ~5.7B km from the sun and the sun is already much dimmer than the description of these stars for PH-1″

    I’ve heard/read it many times that “the Sun would look like just another bright star from Pluto.” Not true. It would actually shine at magnitude -18.7, appearing about 250 times brighter than a full moon (at magnitude -12.7), although smaller in apparent size.

  6. ctj

    so is this hera, hestia, zeus, ophion, or ragnar?

  7. amphiox

    I believe that the description “the sun looks like another bright star from Pluto” actually refers mostly to the angular diameter and not to the brightness, ie from Pluto you can’t easily resolve the sun’s disc with the naked human eye, and it looks like a point source, ie another star.

    In truth it would be a VERY bright star, brighter than even most bright supernovae would appear.

  8. blavag

    Okay I give up, why don’t all these hot Jupiters/gas giants boil away?

  9. Mark

    Let’s call the planet Lagash after the constantly illuminated planet in Nightfall orbiting several suns that suffers through a rare multiple eclipse.

    “If the stars should appear one night in a thousand years, how would men believe and adore, and preserve for many generations the remembrance of the city of God which had been shown!” — Emerson

  10. andy

    The second binary seems to have quite a wide separation. Maybe there is some room for planets in S-type orbits there (though given the faintness I suspect it would be quite an investment of telescope time to find them).

    Like PH-1, that planet is probably a gas giant, but it might have big moons…

    It’s all well and good promoting the concept of habitable exomoons, but given that transiting planets do allow for their detection I have to wonder what kind of limits on satellites can be placed using the existing timing data.

    quaternary is a great word

    I agree, pity the geologists abolished it.

  11. Andrei

    When you said about amatuer astronomers finding the planet I thought you ment something like what Michael Theusner (author of avistack) has done:
    Now that would be an awesome discovery! But still kudos to Michael for thinking about that. And proving it!

  12. rayceeya

    I remember that it was fairly recently many astronomers didn’t believe any planets could form in binary star systems because the extra mass of the second star would disrupt planetary creation, or something like that.

    I was pretty happy they were proven wrong a few years ago when we found the first planets in binary systems. Now we’re seeing planets in “quadinary?” systems.

    Guess it’s hard to keep a good planet down.

  13. Jess Tauber

    Also consider that stars can form in the maelstrom (another great word) of gases flying around the supermassive black holes at galaxy centers, and planets can form from the debris fields surrounding neutron stars after the supernovae which form them.

    Obviously accretive processes are far more robust than they are generally given credit for.

  14. Jon Hanford

    @ andy (#9):

    “…given that transiting planets do allow for [exomoon] detection I have to wonder what kind of limits on satellites can be placed using the existing timing data.”

    Projects like HEK are designed to look into that question:

  15. andy

    In truth it would be a VERY bright star, brighter than even most bright supernovae would appear.

    That raises a point I’ve never been entirely clear on. We haven’t evolved with anything like that in the sky. Now suppose there is a habitable planet around Alpha Centauri A and we manage to send a human being there. Is Alpha Centauri B going to be dangerous to vision: will it cause solar retinopathy, and will it trigger the physiological reactions that prevent us from unconsciously/accidentally looking into the Sun? (Same question could also apply to Alpha Centauri A seen from a habitable planet of Alpha Centauri B).

    I suspect the answer may also depend on whether both suns are above the horizon as if the nearer sun is up the pupils will be more contracted which would help minimise the damage…

  16. I vaguely remember some calculations suggesting that human vision would start to have trouble for angularly-resolved stars not very much hotter than the Sun, if someone looked directly at them (more peripheral vision has lower resolution so it’s a bit more forgiving). The back of the envelope suggests that the two distant companions to PH1 would appear about magnitude -8 from the planet (fainter if projection makes them look much closer than they are from our direction). The closest analog we have in our sky would be the very brightest Iridium flares, only more like the color of Betelgeuse. They’d cast shadows at night, and be visible in a daylight sky with the brightness of ours (I hasten to note that the sky brightness is a huge variable for a poorly-known planet.) Not just a Tatooine sunset, but a Tatooine, umm, starrise.

  17. shunt1

    Fascinating PDF report and I am enjoying studying their data.

    I do find the 20 day orbit a little too close to the possible rotational period of the primary star, based upon the high resolution spectroscopic line broadening. Perhaps they have addressed this in more detail in the report and I simply have not located that information yet. Was this a planet or a large “sun spot” on the primary star?

    However, this detailed research publication is a wonder to read.

  18. Sam H

    @ Mark #9: Nah, let’s wait until we find an actual sextuple system with a planet. I think Asimov should have a more direct real-life analog if we’re going to use that tribute, if you know what I mean :) .

    This discovery is awesome!! Given a habitable planet in a system like that I wonder if humans would even be able to function, given how screwed up the simple Terran diurnal cycle would become.

  19. Steve D

    Blavag asked: “Okay I give up, why don’t all these hot Jupiters/gas giants boil away?”

    You don’t appreciate the gravity of the situation. It’s their gravity. They have so much mass even fast moving atoms don’t escape. Take a cubic kilometer of Jupiter, transport it millions of kilometers away, and it would quickly disperse. The only reason Jupiter doesn’t evaporate is gravity.

  20. shunt1: the 20-day period is that of the central binary star, shown by mutual eclipses as well as radial-velocity shifts. The planet’s orbit around their barycenter takes ~136 (Earth) days. The intensity modulation from a starspot looks sort of like the truncated negative half of a sine wave, while a transit occupies a much smaller fraction of its repeat period.

  21. shunt1

    Planetary orbit: 138.506 days
    Stellar orbit: 20.0002 days.

    Thanks NGC3314, that is why I asked!

  22. shunt1


    Our Sun’s Carrington rotation of 27.2753 days, while Mercury takes 87.969 earth days to complete an orbit, does make me rather suspicious of any orbital period (planetary or stellar) under 30 days.

    Very close orbits start getting into aspects like the exchange of stellar atmospheres and nova effects, not to mention tidal and other physical limits.

    Your explanation of the expected shape of the light dimming was appreciated and I understand the difference.

  23. shunt1

    Beta Lyrae is the classic example that makes me wonder about rapid orbital periods.

    The Roche lobe is the region of space around a star in a binary system within which orbiting material is gravitationally bound to that star. If the star expands past its Roche lobe, then the material can escape the gravitational pull of the star. If the star is in a binary system then the material will fall in through the inner Lagrangian point. It is an approximately tear-drop shaped region bounded by a critical gravitational equipotential, with the apex of the tear-drop pointing towards the other star (and the apex is at the L1 Lagrangian point of the system). It is different from the Roche limit which is the distance at which an object held together only by gravity begins to break up due to tidal forces. It is different from the Roche sphere which approximates the gravitational sphere of influence of one astronomical body in the face of perturbations from another heavier body around which it orbits.

  24. Chris

    @8 blavag
    Why don’t the hot Jupiter’s boil away?
    Let’s assume same composition of Jupiter, which has an escape velocity of 59.5 km/s. (Earth’s is 11.2 km/s). Now assume they are made of hydrogen. We can look at the Maxwell-Boltzmann distribution to see how many atoms will be above the escape velocity. For Earth at 1000 K, about one in a million hydrogen atoms would be fast enough to escape. Meanwhile for Jupiter, you’d need a temperature of 29,000 K. Granted the numbers I picked were a little arbitrary, but it’s not surprising at all that they don’t boil away, at least very fast.

  25. A planet in a quatranry system is very cool, imagine what living in such a system would be like.

    Even cooler is that there is even such a thing as amateur planet hunters. Amateur astronomers have made a lot of other contributions of course, but this is different. Many of those amateurs have been called that only due to their lack of a PhD, they are often bazillionaires that have equipment at home that many colleges can’t afford. Amateur planet hunters could be anyone with free time, good eyes and motivation.

    Despite it’s obvious problems this is a pretty freaking cool world we live in.

  26. shunt1


    I could not agree with you more.

    Eta Aquilae was the first star that I studied using spectroscopy and Beta Laurae taught me about photometry back in 1972. I first learned how to program using the IBM 360 computer at Emery university to process the spectrocopic data that I obtained.

    I chose to become a software engineer instead of an astronomer, but have never forgotten my basic roots.

    Even today, when we selected a new home in Colorado, I required clear skies and unobstructed views to the East and South for my three large telescopes.

    Observational astronomy will always be my love and will never be neglected. I may have some problems with today’s “virtual reality” computer simulations, but will continue to study raw data obtained from new research.

    Dedicated armature astronomers are the backbone of observational astronomy today.

  27. Kevin M

    (“PJK-1″: slip of the finger is a freebie, no points deducted.)

  28. shunt1

    Armature should have been amateur.

    But, I kinda like armature instead, as the dynamo that keeps observational astronomy alive today.

  29. @8. blavag : “Okay I give up, why don’t all these hot Jupiters/gas giants boil away?”

    Some of them eventually do but there’s a lot of gas and mass to boil and blow away!

    One study (published circa 2007) suggests all Hot Jupiters (aka Pegasids or “roasters”) closer than 0.15 AU (24 million km) will eventually be destroyed by this catastrophic evaporation.

    Examples include 51 Pegasi b, Tau Bootis b,and ‘Osiris’ or HD 209458 b which was captured in the process of evapourating away albeit slowly.

    From the wikipedia item linked to my name here :

    In 2003–4, astronomers used the Hubble Space Telescope Imaging Spectrograph to discover an enormous ellipsoidal envelope of hydrogen, carbon and oxygen around the planet (Osiris – Ed.) that reaches 10,000 K. At this temperature, the Maxwell–Boltzmann distribution of particle velocities gives rise to a significant ‘tail’ of atoms moving at speeds greater than the escape velocity, and the planet is estimated to be losing about 100–500 million (1–5×108) kg of hydrogen per second. Analysis of the starlight passing through the envelope shows that the heavier carbon and oxygen atoms are being blown from the planet by the extreme “hydrodynamic drag” created by its evaporating hydrogen atmosphere. The hydrogen tail streaming from the planet is approximately 200,000 kilometres long, which is roughly equivalent to its diameter. It is thought that this type of atmosphere loss may be common to all planets orbiting Sun-like stars closer than around 0.1 AU. HD 209458 b will not evaporate entirely, although it may have lost up to about 7% of its mass over its estimated lifetime of 5 billion years.[26] It may be possible that the planet’s magnetic field may prevent this loss, as the exosphere would become ionized by the star, and the magnetic field would contain the ions from loss.

    There’s also the small issue of a gas giants central rocky core assuming it has one and there are suggestions that some fiery star -brushing “Mustafar” class super-”earths” cvould actually be the leftover cores of Hot Jupiters that have had the outer atmospheres largely evapourated away.


    Great discovery and news, good write up here. Cheers. :-)

  30. Messier Tidy Upper


    There’s also the small issue of a gas giants central rocky core assuming it has one and there are suggestions that some fiery star -brushing “Mustafar” class super-”earths” could actually be the leftover cores of Hot Jupiters that have had the outer atmospheres largely evapourated away.

    Such “Mustafar class” worlds as this :

    one – CoroT exo7b.

    Or this one :

    Kepler 10b – superluminously animated and discussed in the NASA clip there. :-)

    Of course the Pegasids core could be made of diamond rather than rock a la the ‘Space Odyssey’ novels – & a real theory behind that albeit applied to Ouranos and Neptune.

    Which might explain this :

    Recent discovery about 55 Cancris e.

  31. The central binary is made up of a bluish star hotter and brighter than the Sun, ..

    Hmm .. It may appear blue in some images but as an F type “Procyonese” dwarf it’s actually a yellow-white star not a “blue” (type O or B) one.

    Mind you, seen from nearby space it – like our Sun and Procyon and most stars – probably looks blindingly white.

    It is hotter and brighter than our Sun though for sure just like other stars in its class eg. Procyon A, Upsilon Andromedae or Eta Corvi are. (See link in my name for info on the latter incl. hints of an exoplanet there.)

    Summed up in a nutshell from a quick reading of the linked paper; it seems we have here a Procyonese dwarf-red dwarf pair with a Hot Saturn type planet orbiting them and a more distant yellow G-type solar dwarf star paired with a red dwarf orbiting them.

    That, of course, is just for starters – wonder if more exoplanets further out and perhaps smaller also exist in this system still to be found? :-)

  32. shunt1

    I agree, the F type told me that the rotational period should be more rapid than our G type star.

    Now, why would I come to that conclusion?

  33. andy

    Regarding atmospheric escape you should really be considering non-thermal processes. E.g. on Earth the thermal process (Jeans escape) can only explain the loss of hydrogen: if this was the only process going on we’d still have lots of helium in our atmosphere.

  34. @ 34. shunt1 : As a general rule of thumb, higher mass stars with earlier (“bluer”) spectral types generally spin faster.

    Hence stars like Achernar* are flattened due to their exceptionally high rotation rates.

    Not so co-incidentally younger stars also spin faster – it is thought that magnetic field interactions brake a stars rotation rate -and of course the earlier a stars spectral type (eg. O-B) the shorter its lifespan and consequently the less likely it is to have been “braked” and also the more likely it is to have driven away and destroyed its protoplanetary disk.

    There are exceptions to this of course – often but not always linked to companion stars – and slow spinning O-B-A stars tend to frequently have anomalous metallicities and peculiar spectra going on reading from various places especially Kaler’s Stars website which I’d very highly recommend.


    * See linked article by Ken Croswell in my name here. Regulus turns out to have its high rotation caused by accreting matter from a (now) white dwarf companion BTW.

  35. At last, someone who types in four stars, not four Suns, as did everybody else. I did point this out on twitter.

  36. Tony

    Has anyone put together a simulation of this system to watch how the orbits work or how long they may be stable? If so, link please!!

  37. Messier Tidy Upper

    Venturing somewhat off topic but here’s some interesting exoplanetary articles from Ken Croswell in this context :

    A new computer simulation based on the motions of Pluto’s satellites not only zeroes in on the masses of two of the moons but predicts that planets orbiting double stars are more widely spaced from one another than are the worlds of single stars such as the Sun.

    Plus there’s :

    On Hot Jupiters and their implications for other exoplanets in the same system.

    Also additionally, this :

    odd mystery of the disappearing protoplanetary disk.

  38. tall blue ape

    I heard about this on the radio the other morning, unfortunately I can’t remember if it was NPR or BBC, but it was phenomenally bad science reporting! They actually ended up describing a system with the Planet orbiting the binary stars, then the second pair of binary stars orbiting the planet!

  39. Hmm .. It may appear blue in some images but as an F type “Procyonese” dwarf it’s actually a yellow-white star not a “blue” (type O or B) one.

    Have you ever seen Mitchell Charity’s star colours website (linked in my name)

    Early F-stars do seem to come out slightly bluish, the later F-types (of which KIC 4862625 Aa is one, estimated as F8 IV) are pretty much white.

    The usual description of them as “yellow-white” seems to stem mainly from the use of Vega as a standard star, I usually see them as white myself.

  40. Matt B.

    Re: 28 shunt1 – “…when we selected a new home in Colorado…”

    OMG, Phil, the comments are coming from inside the state. Run!


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