Does the planet Fomalhaut b exist?

By Phil Plait | January 31, 2012 7:00 am

Well, this is depressing: Fomalhaut b may not exist.

Fomalhaut is one of the brightest stars in the sky, and is only about 25 light years away — that’s close, on a cosmic scale. It’s young, not more than a few hundred million years old, and surrounded by a vast ring of dust, leftover from the formation of the star itself. The ring is about 20 billion km (12 billion miles) in radius, and has a sharp inner edge.

That last bit is important: the easiest way we know to make the inside edge that well-defined is if a planet is orbiting the star just inside the ring. Its gravity would draw in particles, sculpting what would otherwise be a fuzzy boundary into a clean-cut ring. Not only that, but the ring is off-center; again, that’s likely due to the gravitational influence of a planet.

In 2008, astronomers announced they had found that planet: it appeared in two different Hubble Space Telescope images (shown above; click to embiggen) separated by two years. During that time, it had moved a little bit, by just what you’d expect for a planet at that distance from the star. The news came out the same day as other planets were seen around a different star, and I, along with lots of other folks, made it a headline (see the gallery at the bottom of this post showing all the planets we’ve been able to detect directly in images). This was, after all the first direct detection of a planet orbiting a Sun-like star!

Except, maybe not so much. A new paper has come out (PDF) trying to see Fomalhaut b using the Spitzer Space Telescope. Spitzer is sensitive to infrared, where the planet is far brighter.

And what did they see? Nothing.

Dang.

This image is pretty damning for the existence of Fomalhaut b. It’s the Spitzer infrared observations of the star, with the star’s light carefully removed. On the left is the actual image, and on the right they artificially added a point of light calculated to be equal to what the planet would emit, in the same position the planet should be — that’s what Arrow 1 is pointing at. It should be one of the brightest things in the image (Arrow 2 points to an unrelated bright spot). And while it’s obvious on the right, nothing can be seen on the left, in the real image. In other words, the planet isn’t seen.

Dang again.

Looking over the paper, it’s clear the astronomers were very careful, and did a number of tests. There’s no known way to make a planet as bright as what was seen in the Hubble images yet invisible in the Spitzer images. If the planet were there, they should’ve seen it. Also, a recent study has shown that if the two images show the planet moving, it would be on an orbit that crosses the ring! That seems extremely unlikely, if not outright impossible. A planet that big and massive — more massive than Jupiter — would disrupt the ring in short order if it physically crossed it. That really does make it very, very likely this is not a planet*.

So what is it? It’s probably a clump of dust orbiting the star, reflecting light from the star enough to show up in the Hubble images but not warm enough to show up in the infrared observations.

That’s too bad. If this is true — and it probably is — then that takes away one of the very few planets directly seen in telescopic observations. However, there are still plenty more, and those have been confirmed (again, see the gallery below). And that number will tend to increase as time goes on, even if every now and again it drops by one or two.

Hmph. I once wrote that destroying a planet is hard. Sometimes, all you need to do is try to observe it a different way, and poof! It’s gone.

And now I have to update that gallery, and all my previous pages about it too. Dang science. Always learning more stuff and changing what we thought we knew.

Image credit: Paul Kalas, U C Berkeley; NASA/Spitzer/Markus Janson et al.


* I chatted with an astronomer friend of mine about this, and he agreed with the authors of this new study. "Overall," he wrote me, "it smells like fish.". I couldn’t help myself. I wrote him back: "Of course it does. Fomalhaut is the brightest star in Pisces!"


[Below is a gallery of exoplanets that have been directly imaged using telescopes on ground and in space. Click the thumbnail picture to get a bigger picture and more information, and scroll through the gallery using the left and right arrows.]

exoplanet_betapic3
exoplanet_1rxs1609b
exoplanet_2m1207b
exoplanet_betapicb1
exoplanet_betapicb2
exoplanet_fomalhautb
exoplanet_fomalhautb2
exoplanet_gliese581c_art
exoplanet_hr8799
exoplanet_hr8799b_art
exoplanet_hr8799cspec
hr8799e
hst_hr8799_1998
lkca-15-b_andstar
vlt_betapicb_2011


CATEGORIZED UNDER: Astronomy, Science

Comments (50)

Links to this Post

  1. Friday links | February 3, 2012
  2. Planet Retraction?? « Dr. Erika Grundstrom | February 6, 2012
  1. Chris

    Crap, I already bought several acres. Hope I can get my money back.

  2. ethanol

    Naw it’s just bipolar like Iapetus

  3. llewelly

    They heard Earthlings were coming, and hid their planet behind a nearby star.

  4. So, uh, maybe they just accidently flopped the Spitzer image? :/

  5. F16 guy

    Maybe they don’t WANT to be seen !

    <>

  6. WHAT!? You mean scientists actually look at the evidence and then change their opinions based on what is actually observed? Heresy!

    :D

  7. Red

    Tarkin’s been at it again.

  8. Chris

    @6 Larian
    Facts and evidence are such a pain. So much easier to just make stuff up.

  9. JeffC

    On the bright side this seems like a pretty interesting case of a nascent planet. That ball o’ dust will likely one day be an actual planet.

  10. Minos

    “clump of dust orbiting the star” A future planet, perhaps? Could it still be gathering material from the ring?

  11. Staar84

    Lost a planet, the scientists have. How embarrassing.

  12. James

    My doctor just prescribed Fomalhaut B for me last week.

    Hope it’s not a placebo…

  13. OtherRob

    Oh, man. And I had the Fomalhaut Bs in my Super Bowl pool…

  14. Douglas Troy

    Well, there goes my summer vacation plans.

  15. OtherRob

    @Larian, #6: I’m not a scientist, but that is one of the things I love most about science and scientists.

  16. Jeremy

    Actually, Fomalhaut is the brightest star in Piscis Austrinus, not Pisces. Does that mean the story is only half as fishy?

  17. A6M4

    @kuhnigget My best bet is that the other is that the other arrow points to Fomalhaut a.

  18. “People of Fomalhaut b, your attention please. This is Prostetnic Vogon Jeltz, of the Hyperspace Planning Council. As you will no doubt be aware………”

  19. Torbjörn Larsson, OM

    While I haven’t read the paper, has it really raised any points not already known?

    – Low IR signature:

    “Fomalhaut b is already known as an oddball among exoplanets. It is far too bright in visible light for something expected to be only a few times the size of Jupiter. And ground-based follow-up observations in the infrared have been fruitless, even though this is the part of spectrum where hot, youthful planets are supposed to be brightest.

    Kalas says one explanation may be that the Fomalhaut system is older than previously thought, and therefore cooler and fainter in the infrared. And, he says, the excessive optical brightness can be explained if the planet is surrounded by bright material, just as Saturn is surrounded by a system of rings, which would increase its overall reflectivity.”

    – Crossing the ring (or not):

    “The new data point, and the potential disk-cutting orbit, adds to the mystery. Kalas says it might just be a problem with the latest image. The pictures in 2004 and 2006 were taken using a high-resolution channel on the Hubble’s Advanced Camera for Surveys that failed in 2007 and was not restored when the camera was brought back online in 2009.

    For the latest image, Kalas had to resort to another Hubble instrument, the Space Telescope Imaging Spectrograph. He says the switch to a different detector may explain the planet’s slight deviation from its expected position. He has been allocated time to take another picture with that same instrument next summer.

    If the planet’s unexpected motion persists, he says it is still possible to explain why the disk around the star is undisturbed: perhaps his team is seeing the planet just as some dynamic instability in the star system is knocking it off course.”

    Presumably the 1st point is still valid, and the 2nd is still waiting confirmation if it isn’t just an (expected) calibration issue or even a reasonable orbital change.

    If the planet inside a dust shroud goes for a dust cloud, we are lacking a shepherd planet for the ring, and situated in much the same orbit to boot. Surely the simplest explanation remains the original planet!?

  20. AndySq

    Maybe the Death Star got to it.

  21. lepton

    Phil, any plan on HST to take another shot?

    Maybe HST is too busy for other important stuff.

  22. They should never have placed a Rebel base there.

  23. Chris A.

    @Jeremy (#16):
    “Actually, Fomalhaut is the brightest star in Piscis Austrinus, not Pisces. Does that mean the story is only half as fishy?”

    No, it means that the chances of the direct detection of a planet in this system have gone south.

  24. There’s also the possibility that it is a much lower-mass planet, and surrounded by a cloud of collisionally comminuting swarm of captured satellites.

    A couple relevant papers:

    The Irregular Satellites: The Most Collisionally Evolved Populations in the Solar System
    http://adsabs.harvard.edu//abs/2010AJ….139..994B

    Collisional evolution of irregular satellite swarms: detectable dust around Solar system and extrasolar planets
    http://adsabs.harvard.edu/abs/2011MNRAS.412.2137K

    The second paper discusses Fomalhaut b directly, where they find that a collisional swarm with a mass a few times that of the Moon would be required.

  25. andy

    Of course the question then arises how the clump of dust formed. The paper gives two possible scenarios in the discussion section. One of these hypotheses is that it represents collisions between irregular satellites of an unseen planet buried within the cloud. If so, it would have to be of roughly super-Earth mass or smaller, or it would have destroyed the debris ring by now. The satellite population would be replenished as it passes through the ring, providing fuel for more dust production. Alternatively it may be the remnant of a planetesimal collision.

    However even if there is a planet at the heart of Fomalhaut b, it cannot be responsible for the offset/eccentricity of the debris disc. Maybe there is still an unseen planet out there.

  26. Steve J

    Man, I thought Pluto had problems.

  27. oooa

    Belt-crossing may not be a nail in the coffin — there is the possibility that the object’s orbit is not co-planar with the dust belt. In that case it is only ring-crossing in projection. Coplanarity is not required for secular perturbations to produce the ring offset.

  28. zark169

    I have two questions:
    1) I’m curious, what is bright spot #2 in the picture? Is it a star that is “behind” Fomalhaut by some distance?
    2) Is it possible that the dust cloud (that was detected as Fomalhaut b) is just in the early stages of planet development? The star is relatively young, so is it possible that one or more collections of material are currently forming into planets?

  29. CB

    Well there go my vacation plans. :/

  30. John Paradox

    One word: Galactus!

    J/P=?

  31. amphiox

    Well, the presence of the ring and its properties still strongly suggest the presence of a planet there, doesn’t it?

    And the first planet found orbiting the star Fomalhaut will by convention be named Fomalhaut b, won’t it?

    Seems to me we shouldn’t be saying that Fomalhaut b doesn’t exist. Current evidence still seems to suggest that most likely it does. It’s just that the picture we thought we had taken of it, probably isn’t it.

  32. DigitalAxis

    I thought the scuttlebutt was that we were seeing Fomalhaut’s rings, not the planet itself. In that case you would simply need to find some way for it to reflect lots of optical light, but neither reflect nor emit enough infrared light for Spitzer to detect.

    How do you do that? I’m not a disk or mid-IR specialist, I don’t know. Hopefully someone will tell me if that’s plausible.

    @27 oooa: One interesting and complicating factor here is that Fomalhaut has a distant red dwarf companion, TW PsA. I saw a talk at the latest AAS meeting that suggested gravitational perturbations from these distant companions could explain why something like 1/3 of all planets are not orbiting in the same plane as their parent star’s equator.

    @31 amphiox: THIS Fomalhaut b doesn’t exist. I admit, the distinction gets tricky, particularly with systems like 55 Cancri where people have re-defined the orbits from time to time based on new data- is it still referring to the same orbiting object as before? (usually yes, if the new orbital parameters are within the same range as the old ones)

  33. amphiox

    @31 amphiox: THIS Fomalhaut b doesn’t exist.

    Well, that kind of depends on precisely what it was we gave the name Fomalhaut b to. Was it the specific few pixels we saw on the images and believed to be a planet, or was it to the actual planet presumed to be circling that star, whose existence was inferred from the structure of the dust ring, and then thought to be confirmed by direct observation?

    It’s like a witness picking a suspect out of a pile of pictures, saying “that’s the thief who stole the purse”, but choosing the wrong guy in error. The picture chosen wasn’t the thief, but the thief (most likely) still exists, as inferred from the observation of the absence of the purse.

  34. Dutch Railroader

    Captain, where’s your crew?

    I beamed them down to Formalhaut b.

    But there is no Formalhaut b!

    DON”T YOU THINK I KNOW THAT! There was, but not any more…

  35. Formalhaut b, we hardly knew ye!

  36. Seriously, though, this sounds like we’re gearing up for a rehash of the Pluto argument.
    Obviously there’s a lot of stuff orbiting this star. Even if there were a nice big spherical planet, could it really be said to have cleared its orbit? And given that much material, it’s more than likely that there are some protoplanets in there somewhere. The question I have is, given the apparent size of Formalhaut b, how large would a planetoid have to be to be picked up in these sorts of images?

  37. @ 6 Larian LeQuella Says: WHAT!? You mean scientists actually look at the evidence and then change their opinions based on what is actually observed? Heresy!

    No, no, you don’t understand! They’re just saying that for the grant money. Everyone knows that the government spun the big randomized grant wheel right after the new year. This year, the big bucks are going to “Scientists who doubt the existence of exoplanets.”

    That’s all :-P

    @11 Staar84: Lost a planet, the scientists have. How embarrassing.
    Win!

    @18 ThomasK: “People of Fomalhaut b, your attention please. This is Prostetnic Vogon Jeltz, of the Hyperspace Planning Council. As you will no doubt be aware………”

    This whole thread is a massive orbiting ring of assorted win particles.

  38. Sad news indeed. :-(

    I thought Fomalhaut b had been independently confirmed by other teams & instruments? Seemingly not. [A quick google check seems to say not – only HST could find it – ed.]

    Still I guess that means the honour for first photographically spotted exoplanets goes to ‘Gadolabove’* as I call HR 8799. (Click my name for more on that star and its worlds via kaler’s Stars site.) They, at least, have been confirmed and remain planets right?

    @ 36. Joseph G :

    Seriously, though, this sounds like we’re gearing up for a rehash of the Pluto argument. Obviously there’s a lot of stuff orbiting this star. Even if there were a nice big spherical planet, could it really be said to have cleared its orbit? And given that much material, it’s more than likely that there are some protoplanets in there somewhere.

    Good point – exactly. Plus there’s the fact that the idiotic IAU definition specifically and absurdly excludes all exoplanets from counting as proper planets anyhow. Arrgh! Don’t get me started on that topic..

    Seconding the “win!” for #11 Staar84 & #18 ThomasK too. :-)

    ———

    * Derived from Gamma Doradus variable, Lambda Bootis metal poor star with a Vega style protoplanetary disk – this stars other traits.

  39. Old Rockin' Dave

    “Sometimes, all you need to do is try to observe it a different way, and poof! It’s gone.”
    Schrodinger’s Planet.

  40. @38 MTU: Still I guess that means the honour for first photographically spotted exoplanets goes to ‘Gadolabove’* as I call HR 8799. (Click my name for more on that star and its worlds via kaler’s Stars site.) …

    * Derived from Gamma Doradus variable, Lambda Bootis metal poor star with a Vega style protoplanetary disk – this stars other traits.

    I like it! We really need a naming scheme that goes beyond mythology and constellations and is easier to remember then simple number strings.

    Also, I was interested to see that that star shows about one third the metallicity of the sun. And yet it has at least 4 planets and an extensive debris disk. I’d always sort of assumed that low-metallicity stars just didn’t have much going on as far as planetary systems.
    I wonder if systems like that have significantly more comets than ours? With planets at such a great distance (for flinging KBOs inward), and some of that debris must be composed of volatiles if the system’s metallicity is that low.

    Good point – exactly. Plus there’s the fact that the idiotic IAU definition specifically and absurdly excludes all exoplanets from counting as proper planets anyhow. Arrgh! Don’t get me started on that topic..

    Sounds like I already did :D
    I had no idea about that little clause in the IAU definition, though. Exoplanets don’t count as “proper” planets? How heliocentric of them :-P

  41. andy

    As discussed in the paper, this cannot be an optically-thick disc or ring system: the relative locations of the star, Fomalhaut b and us here on Earth means it would be very difficult for Fomalhaut b to send much visible light in our direction. It essentially has to be an optically-thin dust cloud which leaves the irregular satellite swarm or planetesimal collision remnant scenarios.

    The argument against the collision remnant is that this would be far more likely within the dust ring rather than outside it, so perhaps if this is the explanation we should expect to be seeing more objects like Fomalhaut b within the debris ring. Then again the issues with speckles and image noise mean that we would probably miss such objects within the dust ring.

    Certainly we cannot say that Fomalhaut b represents the direct detection of a planet though… the infrared results show we are not seeing the planet itself even if one is actually there.

    As for planet definitions… oh no not this again…

  42. Captn Tommy

    As I read this blog entry, the thought occured if we are looking a a large clump of dust/debris and it is not a planet, perhaps it is GOING to BE a PLANET.

    Gravity is a strange thing, if there is a clump there is gravity. A visible clump (from 25 ly) means a lot of gravity, which means we are probably looking a preproto-planet, which is far more interesting than a planet (we have a lot of them to study).

    This is something new to study, a clumping dust ball, a super dust bunny, sweeping up more dust as it travels in ond out of the accretion disk. Get a doppler on it see if it is spinning. You Astronomers may have the rarest of rare (for now) a pre-pre-planet.
    I smell papers (mention me as a contributor, please)

    There is no bad Astronomy in this!

    Captn Tommy

  43. ND

    Dutch Railroader,

    Nice :)

    Probably the best scene in STOS. William Windom outdid Shatner :)

  44. what are the chances of the supposed planet moving faster or on a different than assumed orbit?

    …..
    Red Matter or Parallax, your choice :P

  45. It’s 2012 ya know. So that can only mean that it WAS there at one time, but is now on it’s way to intercept Earth as… (cue music) FOMALHAUT X! (echo,echo,echo…)

  46. Matt K

    The planet still hasn’t been ruled out – if you look at Figure 2 in the paper, the planet could be 1.0 Jupiter masses (with an age of 400 Myr for the planet) and still not be detected. The original 2008 paper even stated a limit of 3 Jupiter masses from dynamical arguments. (Why? If Fomalhaut b is greater then 3 Jupiter masses, its gravity would have ripped up the large dust ring seen there).

    The authours have done a very nice job with the data reduction and demonstrating that they have the sensitivity for their reported results, so it is a very solid upper limit there.

    Regardless, it was known from the first paper in 2008 that we’re almost certainly looking at a cloud of dust. The issue is whether the dust is in orbit about a planet (we can’t see the planet’s flux because its surface area is so small) or is it a gravitationally unbound clump of dust from a recent collision?

  47. andy

    @Matt K: the orbit postulated for this object was initially calculated assuming that this is the object responsible for the eccentricity of the debris ring. If the ring-crossing orbit is correct, the mass must be far lower than the initial estimates: an upper limit of 10 Earth masses is given in the paper, so we may well be looking at a super-Earth planet or smaller. According to Kennedy & Wyatt (2011) “Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets” it may even be possible that Fomalhaut b is a binary planet… time for the space artists I think!

  48. Ole

    I hear that the people of Formalhaut b has issued a statement that the Earth does not exist.

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