Astronomers find a planet denser than lead

By Phil Plait | October 6, 2008 10:50 am

Planets circle the stars that dot the heavens.

Before 1995, we couldn’t have said that with any certainty. Now we know of more than 300 planets orbiting distant stars, and we have a fleet of telescopes looking for them. The ultimate goal is to find another Earth orbiting a star like the Sun, but the quest on the way to that Holy Grail has yielded some strange benchmarks.

CoRoT-exo3b, a dense planet orbiting another star
COROT-exo-3b compared to Jupiter

Meet the planet COROT-exo-3b. It orbits a star slightly larger, hotter, and brighter than the Sun. The star is not an unusual one in any way, but the planet is definitely weird: it orbits the star in just over 4 days, which is pretty close in, though not a record breaker in and of itself. What’s bizarre is that it has about the same diameter of Jupiter, but has 21.6 times Jupiter’s mass. That makes it denser than lead.

If I could stand on the surface of this planet, I’d weigh 4200 kilograms*. That’s over 9000 pounds!

Oof.

This is by far the most massive planet found so close to its parent star. There is another extrasolar planet found with about that mass, but it orbits its star much farther out. The ones we’ve found that orbit their stars so close tend to have masses much smaller than this. For comparison, Jupiter takes 12 years to circle the Sun once. Mercury takes 88 days. So we’re talking big planets, really close to their stars.

This planet is challenging to models. How did it form? It most likely formed farther out from the star — gravitational influences make it hard for a large planet to form close to a star — and then gradually moved in. This can happen due to friction, of all things: when the star and planet are young, there is a disk of material leftover from the planetary formation. As the planet sweeps through this material it slows its orbit. It spirals in due to drag gravitational interaction with the disk, and eventually settles down when the disk material thins out a few million kilometers from the surface of the star itself.

The mass of this newly discovered planet is pretty freaky. Normally, anything with a mass more than about 15 or so times the mass of Jupiter would be considered a brown dwarf, a "failed star", as some people call them (I don’t). But at the lower end of the brown dwarf mass range, it gets a bit hard to tell the difference between a planet and a BD. Some people say planets and BDs form in different way (planets grow in size from smaller bodies building up over time through collisions, while BDs and stars form from the collapse of material in a nebula); but I don’t like this definition. You could have two objects that look precisely the same, yet one could be a planet and the other a BD, just because they formed in different ways. That strikes me as silly.

Either way, COROT-exo-3b is weird.

It was discovered by COROT, an orbiting European Space Agency mission designed to look for stars that dip in brightness as an orbiting planet passes in front of them. That gives the size of the planet (the amount the light dims is proportional to the size of the planet). The mass was found using ground-based telescopes, by measuring the amount the planet tugs on the star as it orbits. That’s how the incredible density of this object was found.

As we search the sky for Earth analogue planets, we’re bound to find things at the limits of our understanding. This ultra-dense ball of compressed matter certainly falls into that category. And we’re still new at this! What else lies out there at the fringe of our knowledge?


*For those of you who want to complain about my use of mass as a weight, read this, and acknowledge my superior logical skills. However, given the amount of sturm and drang this has caused among people, I’ve decided to simply strike through the part that has given everyone the vapors.

CATEGORIZED UNDER: Astronomy, Cool stuff

Comments (122)

  1. Todd W.

    Has there been any word yet as to what this planet might be made of?

  2. Duane

    Is the “30 planets” reference a typo? It seems we know of far more than 30. Perhaps 300?

    Either way, I wonder what it’s “Hill Sphere” radius would be!

  3. Duane

    Its, not it’s….

    And I’m an English major, too….

  4. That should be “more than 300 planets” in the first line. And while “certainty” w.r.t. the existence of exoplanets came about in 1995 and esp. 1996 with many more discoveries, it’s worth noting that some of the exoplanets announced before 1995 later turned out to be real after all.

  5. Ibeechu

    Vegeta, what does the scanner say about Phil’s weight (in pounds) on COROT-exo-3b??

    IT’S OVER NINE THOUSAAAAAAAAAAND!

    I so had to do it.

  6. eric

    Question on planet searches – how many systems did we look at to find those (over 300) planets? i.e. in about what percent of systems in which we look for planets do we find them?

  7. JohnW

    “This can happen due to friction, of all things: when the star and planet are young, there is a disk of material leftover from the planetary formation. As the planet sweeps through this material it slows its orbit. It spirals in due to drag, and eventually settles down when the disk material thins out a few million kilometers from the surface of the star itself.”

    Wouldn’t leftover material in the planet’s orbit be moving at the same velocity as the planet? How could that cause drag?

  8. To someone whose only knowledge of astronomy comes from the intertubes, it sounds like a binary system with a normal star and a brown dwarf. How is this different?

  9. whb03

    Love to see the ID-ers try to deny the existence of gravity while standing on this baby…

    Quick question: since it is so dense, does it really matter what it is made of? Seems like if it is a mini-brown dwarf-type object, it would simply be dense no matter what it is made of…

    THIS is why I absolutely love this blog! This is the coolest find so far this year (to me at least).

  10. Here’s a sticking point for the stickler:

    For someone who uses the word “masses” instead of weighs, do you really want to start telling people that you “weigh” a certain number of kilograms?

  11. tai

    Thank you, Ibeechu, I read the comments in hope someone would make that comment, and you have not disappointed!

  12. Oops. Fixed the “30” typo. I don’t know if I am making more typos lately, or my keyboard is failing. It’s making a squeaky sound sometimes, and I wonder if some of the keys are going bad.

  13. Todd W.

    @Phil

    It must be because Mercury is in retrograde.

  14. tacitus

    This can happen due to friction, of all things: when the star and planet are young, there is a disk of material leftover from the planetary formation.

    I think this is overstating what we know. It’s probably more accurate to say “This might be happening” — i.e. it’s our best (educated) guess after running all kinds of numbers and simulations.

    Either way, I’m a big fan of COROT. They have a ton of light-curves left to be analyzed, and will no doubt turn up dozens more planets once all the analysis and follow-up work is completed. They are still hoping that they will be able to catch a couple of true terrestrial-type planets before the mission is over. That would be cool.

  15. Nick Rudzicz

    “If I could stand on the surface of this planet, I’d weigh 4200 kilograms. That’s over 9000 pounds!”

    Forgive me if I’m wrong, but isn’t mass invariant?

  16. Wow, that’s pretty cool! Although, the subject of density got me thinking. Does anyone else think this planet may be the source of cranial coverings for the folks we seem to elect? :P

  17. Ibeechu

    Nick, mass is invariant, but that’s why Phil said “I’d weigh…” and not “I’d mass…” The confusion comes when these sciency folk use grams as a measurement of weight and not mass.

  18. From:

    http://exoplanet.eu/star.php?st=CoRoT-Exo-3&showPubli=yes&sortByAuthor

    Mass = 21.66 Jovian masses
    Radius = 1.01 Jovian radii
    Semi-major axis = 0.057 A.U.
    Orbital period = 4.26 days

    So its average density should be 21.0 times Jupiter’s or 27.9 grams per cubic centimeter. This is 2.46 times the density of lead (11.34 grams per cubic centimeter). Its surface gravity is 21.2 times Jupiter’s or 53.7 g’s.

    Before we start looking for exotic matter to explain this high density we should remember that a M9V red dwarf has an average density of 314 grams per cubic centimeter and a surface gravity of 497 g’s and it’s made of mainly hydrogen. So no exotic matter is necessary to reach very high densities and very high surface gravities.

  19. Law Mom

    It’s stuff like this that makes me wish I had gone into astronomy. Honestly, I think I hang out her to absorb some of that thrill, like a groupie who wants to be a rock star.

    If I were an astronomer, I would so study planets. I am always amazed at the variety in our own solar system, in size, density, atmosphere, satellites, etc., etc, etc. Mars and Jupiter–could they be more different! Now we are finding even more strange and unique things surrounding other stars. Awesome. Planets are like the fingerprints of the universe, no two are exactly alike.

    Keep it coming, astronomers!

    (And now, back to real estate fraud, sigh…)

  20. In a word: Whee!

    This is why real science is so much better than the made up stuff. We go out looking for what might really be going on, what’s really out there, and so on. The reality is stranger and more beautiful, and has the bonus of being real.

    Now maybe the planet turns out not to be what it currently looks like. But that, too, is part of the adventure of real science. Keep looking and trying to figure things out.

  21. JohnW, good catch. The evolution of this mistake is funny.

    I originally wrote “dynamic friction”, which is a process where gravitational encounters can change an object’s orbit. I thought about it for a second, then decided to just keep writing and get back to that phrase.

    After I was checking the article, somehow dynamic friction lost the adjective, and then somehow in my head turned into “drag”. A series of small evolutionary steps that led to my writing down the wrong thing. :-) I’ve corrected it, with a link to a more detailed explanation. Thanks!

  22. GaterNate

    Very cool discovery!

    “The ultimate goal is to find another Earth orbiting a star like the Sun…”

    I often wonder what would be the reaction among astronomers if an Earth twin was found orbiting a star very unlike the sun, somewhere earths aren’t supposed to be, such as a blue star like Regulus. Would the general consensus be that we’ve been wrong about some aspect of planet formation or perhaps about stars’ lifespans? Might there be serious speculation that an earth with a blue sun may be the work of highly skilled and advanced terraformers? Anyone have any thoughts?

  23. Nick Rudzicz

    @Ibeechu: Yeah, that’s what I suspected. Easier than saying “On planet P1 I’d weigh the equivalent of mass M as measured on planet P2, in other words…etc. etc.” Oh, and I just noticed…@Phil, now I remember that post. Blame my internal grade 7 student for getting excited over what he thought was a typo ;)

    On another note, if the planet is denser than lead, does that give us an indication as to its age (i.e., heavier elements -> much later-generation stars -> much older)?

  24. Overlord

    What, 9000?!

    That’s some awesome stuff right there. Amazing the things just out of our (current) reach :)

  25. mighty favog

    Anyone remember “Mission of Gravity,” Hal Clement’s novel that featured a huge terrestrial planet? His planet rotated rapidly and was disk-shaped, so that there was 700 g at the poles and only 3 g at the equator. My gut feeling is that a planet of such shape and rotation wouldn’t maintain structural integrity.

    But I’d be interested to know if any real scientists have hypothesized such a planet as large and dense as COROT-exo-3b.

  26. IVAN3MAN

    There are two types of planetary migration:

    Type I migration

    Terrestrial mass planets drive spiral density waves in the surrounding gas or planetesimal disk. An imbalance occurs in the strength of the interaction with the spirals inside and outside the planet’s orbit. In most cases, the outer wave exerts a somewhat greater torque on the planet than the interior wave. This causes the planet to lose angular momentum and the planet then migrates inwards on timescales that are short relative to the million-year lifetime of the disk.

    Type II migration

    Planets of more than about 10 Earth masses clear a gap in the disk, ending Type I migration. However, material continues to enter the gap on the timescale of the larger accretion disk, moving the planet and gap inward on the accretion timescale of the disk. This is presumably how “hot Jupiters” form.

    Click on the link for more information and a movie simulation of planetary migration.

  27. themadlolscientist

    It’s made of creationist brains. Meow! =^..^=

  28. kuhnigget

    Planet denser than lead? Pffffft! If you include the Earth’s biosphere in the equation, particularly the density of homo sapiens sapiens, I’d wager we’ve got that one beat by a long shot.

  29. But I’d be interested to know if any real scientists have hypothesized such a planet as large and dense as COROT-exo-3b.

    Sure they have. I’d provide links for the following references, but links are a good way to end up in the moderation queue, so I’m going to let you do the Googling :-) . I suggest you check out Mordasini et al. (2007) “Giant Planet Formation by Core Accretion” which predicts formation of planets by accretion in this kind of mass range.

    Furthermore the fact that once you get past roughly 1-2 Jupiter masses, the radius of the planet doesn’t change much is also quite well known: see Baraffe et al. (2003) “Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458″ – the tables at the end of the paper give radii similar to that of Jupiter for objects with 0.02 solar masses (roughly the mass of CoRoT-Exo-3b). In fact the discovery paper for CoRoT-Exo-3b (Deleuil et al. 2008, “Transiting exoplanets from the CoRoT space mission. VI. CoRoT-Exo-3b: The first secure inhabitant of the Brown-dwarf desert” – it’s available on the Extrasolar Planets Encyclopaedia website’s Bibliography section) mentions the fact that this object sits very nicely on predicted mass/radius relationships for this kind of object.

  30. Quiet_Desperation

    It’s planet Moab, aka Warzone 1.

    That’s a very obscure Alan Moore reference is anyone is wondering.

  31. Mu

    Regarding the “no exotic matter” comment, anything above a density of 22.5 is not composed of what we would call “regular matter” as expected in an ordinary planet. To get to higher masses you need a gaseous compressed plasma state, like in the star example. That’s pretty exotic for something described as a planet IMO. Plus. whatever it’s made off, so close to its star you’d think it would get blown to pieces by solar winds combined with surface evaporation.
    Probably a good candidate for the location of the super max prison in the next Riddick movie so.

  32. I’m assuming that just because the planet is denser than lead doesn’t mean it needs to be made of an element or combination of elements that are denser than lead in our local frame of reference (Earth). Couldn’t it be made of Dirt (or regolith) that was just compressed much more than we would see as “normal”?

  33. …has 21.6 times Jupiter’s mass. That makes it denser than lead…

    …and a brown dwarf instead of a planet. Brown dwarfs all the way to low-mass red dwarfs have approximately the radius of Jupiter, nothing unexpected here. Brown dwarfs and the smallest stars are really dense objects; imagine an 80 Jupiter mass red dwarf/brown dwarf no bigger than Jupiter! It has a density far beyond lead and huge surface gravity.

    Even if this “planet” is a brown dwarf, it is unusual because Sun-like stars for some reason don’t seem to have close-in brown dwarfs. Planet searches should have spotted a large number of them since they’re much easier to detect, but that hasn’t happened. So we know they’re rare.

  34. @IVAN3MAN: “There are two types of planetary migration”

    It’s interesting that the model used assumes circular orbits. I seem to recall an article by Geoff Marcy where they computed the average eccentricity of exoplanets to be 0.25 which is quite huge by solar system standards.

    http://astro.berkeley.edu/~gmarcy/marcy_japan.pdf

    “However, planets orbiting beyond 0.1 AU (i.e. not circularized) have a median eccentricity of e = 0.25 with a standard deviation of 0.19. Thus, the orbital eccentricities of giant planets within 5 AU are considerably higher than those in our Solar System.

    .
    .
    .

    However, the most massive planets, notably those with Msin(i) > 5 MJup, exhibit systematically higher eccentricities than do the planets of lower mass. This cannot be a selection effect nor can it be caused by errors because the most massive planets (right half) induce the largest Keplerian amplitudes, K, allowing accurate determination of eccentricity.

    If planets form initially in circular orbits, the high eccentricities of the most massive planets in Fig. 5 poses a puzzle. Such massive planets have the greatest inertial resistance to perturbations that are necessary to drive them out of their initial circular orbits. Yet the massive planets reside mostly in orbits more eccentric than the lower mass planets. We remain puzzled that the most massive planets have the highest orbital eccentricities. Perhaps massive planets formed by a process in which the orbits are not initially circular.”

  35. gravitational influences make it hard for a large planet to form close to a star

    Actually, it’s less gravity (directly) and more temperature. It’s neigh inescapable that the inner sections of the disk will be hotter than the other portions (even before the proto-star really heats up) and at some point, ices can’t form. Since hydrogen compounds (water, ammonia, methane) are the biggest fraction of the disk mass after hydrogen and helium (which pretty well will never solidify in the disk), losing them means not building really big planets.

    JohnW:

    Wouldn’t leftover material in the planet’s orbit be moving at the same velocity as the planet? How could that cause drag?

    Actually… no. Gas orbits at sub-Keplerian speeds because gas pressure helps resist gravity. So a larger body will feel a headwind as it moves through the disk on a Keplerian orbit. However, if memory serves this effect is unimportant for planet-sized bodies. As IVAN3MAN noted, the cause of migration is a bit more subtle. (There’s also a Type III migration now, but I forget the details.)

    As a general note, it isn’t that surprising to find a super-dense planet about the radius of Jupiter. Our largest planet is actually not too far from the point where adding more mass actually results in a smaller radius (and thus a much denser body).

  36. “Regarding the “no exotic matter” comment, anything above a density of 22.5 is not composed of what we would call “regular matter” as expected in an ordinary planet.”

    Hmmm, COROT-exo-3b has an average density of 27.9 grams per cubic centimeter. The densest element on earth is osmium with a density of 22.6 grams per cubic centimeter. So COROT-exo-3b has an average density only 23 percent higher than certain forms of matter on the earth. That’s not terribly exotic. Still, if I had to bet I’d say it’s made of hydrogen and helium rather than osmium. I wonder if they already have a spectrum on this guy.

  37. Duane

    A quick napkin-scribbling calculation, assuming a stellar mass of 2×10**30 Kg (similar to the Sun’s), a mass of 4.2×10**28 Kg (Jupiter mass x 21), and an orbital radius of 5,000,000 Km, the Hill Sphere radius of just under a million kilometers.

    Just having fun…. ;)

  38. dkary

    Just to follow on from John Weiss’ excellant comments (meaning he said what I wanted to say but beat me to it!): yes, gas disks are sub-keplerian, but the optimal size for drag is in the few meters to 1 km size range. Anything bigger hardly notices the drag on disk-lifetime scales.
    (Back when I was working on this we considered it a bit of a problem, since it means accretion through that size range has to be rather quick or you loose all your planetesimals into the star. However, once you get a few larger planetesimals forming then this drag affect will pull more small stuff into the feeding zone of the larger body.)

    However, as others have described, there are much better ways to cause migration in larger bodies, so that may be important here.

    Just to clarify what some other folks are saying, it is likely that the composition of this newly discovered “world” is mainly hydrogen and helium. As you add more hydrogen to a planet like Jupiter, the extra gravity causes the hydrogen to become more compressed (hence denser), without increasing the radius much at all. In fact, in some regimes the radius gets smaller as the mass goes up! This trend continues until the core gets hot enough for sustained fusion to become important, and that extra heating keeps the radius much larger than Jupiter size.

    What I’m wondering is if there really is any way at the moment to distinguish between a “star-like” formation process (gravitational collapse) vs. a planet-like formation process (accretion + gas accretion) in a body like this one? I suspect that the condensed matter models are not up to distinguishing between a hydrogen world with a 10 Earth-mass denser core and one without such a core. Anybody more up-t0-date than I am on the state of giant planet interior modelling?

  39. dkary – Google a paper called “Structure and evolution of super-Earth to super-Jupiter exoplanets. I. Heavy element enrichment in the interior” by Baraffe et al. (2008) – it has a section about massive planets (in the brown dwarf range) with massive cores.

  40. “Structure and evolution of super-Earth to super-Jupiter exoplanets. I. Heavy element enrichment in the interior”

    That’s a tough one to find. Lots and lots of URLs containing only the abstract but I did find the main article:

    http://xxx.lanl.gov/PS_cache/arxiv/pdf/0802/0802.1810v1.pdf

  41. Weird stuff

    ” (planets grow in size from smaller bodies building up over time through collisions, while BDs and stars form from the collapse of material in a nebula); but I don’t like this definition. You could have two objects that look precisely the same, yet one could be a planet and the other a BD, just because they formed in different ways. That strikes me as silly.”

    Actually, I kinda like that there is a distinction. Something that was once a star or substar should have a name other than “planet”.

  42. Jiff Weeder

    Now that sounds like it would be a cool planet to live on!

    Jiff
    http://www.privacy.es.tc

  43. This is truly a fascinating find!

    Thank you Phil!

  44. Could it be a Dyson Sphere? Cool stuff indeed!

  45. From the article:

    “This shows that planets can exist with masses up to ~10 MJupiter, well above the opacity-limit for fragmentation, m = ~3-5 MJupiter (Whitworth & Stamatellos 2006), the expected minimum mass for brown dwarf formation. These two distinct astrophysical populations should then overlap over a substantial mass domain.”

    Hmmm, planets and brown dwarfs can overlap in mass even though they are apparently different. Apparently some of these planets can ignite deuterium fusion and yet they are still not brown dwarfs.

  46. Rob

    No, you would not weigh 4200 kilograms; you would weigh whatever you do now. Kilograms are a unit of mass, and do not change based on gravitation differences. Pounds, though, are a unit of force, and will change based on gravity, so you would weigh over 9000 pounds, assuming the rest of your calculations are correct.

  47. What exactly does it mean to “weigh 4200 kilograms”? I sense a dimensional disjunction. :)

  48. Brian Kaufman

    Phil!

    I am appalled that you wrote that you would weight 4200 kilograms on this planet. I shouldn’t have to explain why that doesn’t make any sense. I’m guessing you mean you would weight the same as a 4200 kg object does on Earth. Even so, it is a weird thing to write and makes no sense to me.

    B

  49. Andrew

    > # Nick Rudzicz Says:
    > October 6th, 2008 at 11:34 am
    >
    > “If I could stand on the surface of this planet, I’d weigh 4200 kilograms. That’s over 9000
    > pounds!”
    >
    > Forgive me if I’m wrong, but isn’t mass invariant?

    Nick is absolutely correct. Mass is invariant. Unless you weigh 4200 kg on Earth, you wouldn’t weigh 4200 kg on this planet. You *would* weigh 9000 lbs, but pounds are a measure of force, not mass.

    Shouldn’t a science writer know this?

  50. Of course I know my actual mass won’t change. Please.

    However, I use metric units on this blog first, imperial second. The metric unit of weight is something no one ever uses. On Earth, a kilo weighs 2.2 pounds. However, in other countries when you ask someone their weight they will give it in kilos, even though it’s a mass, not a weight. It’s used colloquially.

    In this post I use “kilos” and “mass” colloquially as well. It may cause some confusion among people who know science, but people who are casual readers will know exactly what I mean. I could have taken two or three paragraphs to explain all this, and interrupted the flow of the post, just to satisfy a handful of people, or I could have simply assumed people understood what I meant.

    A third choice, which I toyed with, was to simply leave the metric unit off. But I don’t like to do that. A fourth choice would have been to use Newtons. Who would’ve understood?

  51. “I am appalled that you wrote that you would weight 4200 kilograms on this planet. I shouldn’t have to explain why that doesn’t make any sense.”

    If you buy a digital scale from WalMart and you set it to units of kilograms, what is it actually measuring, mass? I think not. So yes, strictly speaking kilograms can only be used as a unit of mass, but informally we can use it to mean number of newtons divided by 9.8. At least he didn’t say he would weigh 288 slugs. :)

  52. justcorbly

    Do we have reason to believe that the clouds from which solar systems form are always uniform in their composition and structure? If not, then clouds with differing composition and structure would form planets of different composition and structure. Maybe that accounts for the variations we see.

  53. “A fourth choice would have been to use Newtons. Who would’ve understood?”

    So if being correct is too hard to understand, you perpetuate a common and serious error? Come on!

    Newtons are correct and international. Pounds are correct but regional. kilograms are WRONG!

  54. Nick Rudzicz

    “A fourth choice would have been to use Newtons. Who would’ve understood?”

    Coincidentally, my friends refer to me as Newton. Honestly, that would have been far too much confusion for me on a Monday.

  55. I think the commenters have caught the main points.

    The only other thing to note is that this was announced (and got a fair amount of play around the astrosphere – Dynamics of Cats, Centauri Dreams, etc.) back in May. So score another victory for ESA’s policy of announcing all discoveries twice and relying on the short memories of the lemmings.

  56. PG

    Newtons are correct and international. Pounds are correct but regional. kilograms are WRONG!

    I will never understand the obsessive need that some have for everything on the internet to be 100% correct all of the time…. Given that the millions of people refer to their weight in kg everyday are WRONG, it must be hard for these people to sleep at night. Somehow, I manage.

  57. IVAN3MAN

    Just to chip in my 10 cents’ worth in this mass verses weight debate, this is an extract from Wikipedia on the subject of weight:

    In commerce and in many other applications, weight means the same as mass as that term is used in physics. In modern scientific usage, however, weight and mass are fundamentally different quantities: mass is an intrinsic property of matter, whereas weight is a force that results from the action of gravity on matter: it measures how strongly gravity pulls on that matter.

    However, the recognition of this difference is, historically, a relatively recent development and in many everyday situations the word “weight” continues to be used when “mass” is meant. For example, we say that an object “weighs one kilogram”, even though the kilogram is a unit of mass.

    Click on the links for a more detailed explanation.

  58. Grand Lunar

    Say, isn’t this the planet Krypton?

    I wonder if this could be the core of what used to be a brown dwarf, with it’s outer layers stripped by solar (or is that stellar) wind.

    The truth might be even stranger than we know. As if this isn’t weird enough!

  59. Daniel

    It will be so cool when we can actually SEE these planets (not their shadows) through some sort of telescope.

  60. Vagueofgodalming, I checked my email and my blog, and saw no mention of this from May (and I don’t always keep up with all the other blogs). But hey! Thanks for insulting me, and everyone else who wrote about this, and all my readers, too!

  61. Anonomous

    OVER NINE THOUSAND!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    I hope no one beat me to it.

  62. Why do articles like this always say the scientists found a planet? Why Before 1995, we couldn’t have said that with any certainty. Boy that’s news to me because before 1995 I read many articles claiming scientist found a planet, this or that, but they never said in the article we can’t say that with certainty! Never once have I seen an article say that before 1995. What happened in 1995? How can they find a planetwith certainty now and not then? Sorry for sounding so stupid, but if you can’t simply say why in a brief statement, it looks to me like you are hiding something, just like before 1995 the articles I read were hiding the fact that they couldn’t be certain. Why can’t the authors of these scientific articles ever be totally truthful? The report theories as fact and ignore real facts, and then in their elitist minds expect respect.

  63. To hopefully cause people not to hyperventilate, I have struck through the offending comment.

  64. on a side note… why are newtons such an uneven measurement?! everything else in metric works out nicely in the decimal system, but not that one? (would probably explain why it’s never going to be popular)

    also, it really bugs me when Americans get righteous about the use of “kilogram” in colloquial speech. unless science decides to trademark all words that are used differently in scientese than in common language (“theory” comes to mind) so that they can only be used with their scientific meaning, we’ll all have to continue to take words in context. (and obviously weighing kg is colloquial, massing kg is scientese)

    [/rant]

  65. @Phil
    “The metric unit of weight is something no one ever uses.”

    Well almost no one. I filled out a bank form with “height – 1.94m, weight 980N” I stopped short of providing peak absorption in nm for eye colour…

    @IVAN3MAN
    That makes more sense, and it makes sense in Phil’s old post about massing stars – the term “weight” can be used to mean mass. But that still makes using units of mass to describe gravitational force wrong. Sorry Phil. We know what you mean, and we still love you. But it’s wrong.

  66. Me

    Is it possible that our planet is inching closer to the sun? I started to wonder this while reading the article and couldn’t find an answer online.

  67. IVAN3MAN

    @ Tom Marking

    Thanks for the PDF file link(s). Interesting reading!

    @ John Weiss

    The post I made above on the subject of Type I & Type II planetary migration was gleaned from Wikipedia (which needs updating!), but with further Googling, I found these two interesting links on Type III planetary migration:

    http://online.itp.ucsb.edu/online/planetf_c04/artymowicz/

    http://www.diva-portal.org/su/abstract.xsql?dbid=7461

  68. Agarthan

    Can you explain to me how just restating your mass/weight figure in different units – in this case, using Imperial instead of metric units for mass – changes what’s being said?

    The whole confusion is that 100kg of /mass/ will always contain the same /amount/ of matter, yet will manifest different /weights/ in different local gravity conditions. Floating about in space, for example, you have no weight (thus ‘weightless’), but retain all your mass (and therefore your momentum, m*v, as you careen around the space capsule). On this massive (!) planet/dwarf, you would have enormous weight, but still mass 100kg (or whatever your mass is).

    Also: please stick to grams or kilograms, rather than imperial. You may be in the U.S. (just guessing here), but last I checked astronomy uses metric units, by international agreement. :) love the blog btw!

  69. Sasquatch, are you kidding? You’re using the word elitist like that?

    And you might try to use something, say, Google. I bet you can find your answer in less time than it would take me to write it out.

  70. Scott

    It’s OVER 9000!

  71. Jason

    Who can we lobby to name this new, densest planet, planet “Bush”?

  72. earthling

    I enjoyed the kg, lb, mass, weight discussion immensely. Did somebody lament the fact the newtons don’t work out “evenly” in the decimal system? Heck, 9.8 kg m/s^2 is pretty close to 10! Nonetheless, newtons are genuinely a confusing unit. Didn’t NASA loose a Mars probe because someone confused newtons and pounds?

  73. st0ner

    Woah. imagine what the weed must be like there?

    dense?

  74. Rahne

    @Ibeechu

    Yes. It had to be done :)

  75. Shagata Ganai

    Not to be a prig, but it’s “sturm und drang”. Strumming is for ukeleles.

    Nice writeup on a wierd ball of….something!

  76. D’oh. Stupid typo. I fixed it. In fact, ich spreche ein bisschen Deutsche. Vielen Dank.

  77. Man, you “mass is invariable” types are annoying. Nothing’s more annoying than pretending not to understand something when you know exactly what the writer meant to say. How about we create a new unit called kkilograms that equals 2.20462262 pounds and has nothing to do with mass. There, now he weighs 4200 kkilograms on the surface. Happy now?

    No wonder the metric system isn’t taking off in the States.

  78. BTP

    Kamal-
    Good catch- if we did find something akin to a Dyson Sphere, who’s
    to say it might not appear something like this?

    As weird as the mass is, the orbital distance and time are, well possibly even weirder?

    What a bloody interesting find……

  79. dkary

    Many thanks to the folks who led me to the Baraffe et al. paper. It looks like they’re trying some neat stuff.
    I’ve only given it a quick look through, but it looks like they are focusing mostly on smaller planets and/or ones that have a very high metalicity. Can you make a 20 Jupiter mass planet only a small (e.g. 10 Earth mass) core and only modest amounts of metals in the envelope? The only comment I saw that goes into that regime seemed to be saying that when you have that little metal it doesn’t matter much how it’s distributed the radius is going to be the same.
    That suggests to me that it would be hard to tell the difference between a “true” brown dwarf and an oversized jovian: they would even both go through deuterium fusion early in life.

    Of course, if it’s got one of these 600 Earth mass cores that they are discussing, then you might be able to notice the difference.

    DK

  80. Lowbacca

    Comments:
    1. It should totally use Newtons.

    2. Newtons don’t come out easily because the equation is F=ma.
    We defined meters, seconds, and kilograms as we wanted, but the acceleration on earth has a factor from the Gravitational constant in it. We’d have to redefine what meters, seconds, or kilograms are to get Newtons to be more managable because of that.

    3. Sasquatch. We’ve gotten better at it. Some are still not entirely certain, but the techniques have improved and the equipment has improved. This is generally called progress.

  81. Tatsuhoshi

    To everyone who has an issue with kilograms as a measure of weight: Grow up.

    Kilograms (Metric) measurement has been the world standard for weight for MOST of the world a very long time. For most of that time, America was the ONLY country that used ‘standard’ measurements of pounds and ounces as the common measurement (which is why all international food packaging and industrial labels possess the weight in BOTH kilograms and pounds).

    For anyone wishing to be understood by the general populace, including countries that still use metric as the standard (which would STILL be most of the world), presenting the weight of a person in kilograms and pounds BOTH is considered to be standard practice. He is not wrong as a WRITER of an article meant to be presented to the GENERAL PUBLIC.

    So what if you have a physics or chemistry or astronomy degree. There is a difference in presentation to common masses and informed specialists. This has been, and always will be the case. If you’ll note, he avoided any heavy terms throughout the article that would simply confuse the average reader. Using kilograms as a measurement of weight is nothing but an extension of this idea of presenting the information as common knowledge, and not something that will only be read by those with degrees and specializations.

  82. Nigel Depledge

    Quiet Desperation said:

    It’s planet Moab, aka Warzone 1.

    That’s a very obscure Alan Moore reference is anyone is wondering.

    Not so obscure, methinks! At least, not to anyone who’s read The Ballad of Halo Jones (vol 3).

    Anwo koyok ga!

    (Now, that’s an obscure reference!)

  83. Nigel Depledge

    The BA said:

    However, I use metric units on this blog first, imperial second. The metric unit of weight is something no one ever uses.

    I must take issue with you here, Phil. The SI unit of “weight” is the Newton, because “weight” is a force, just like any other. I think you will find that a great many people use Newtons on a regular basis. (Something that NASA learned to its cost when the Mars Climate Orbiter [IIRC] went missing, due to a failure to convert Newtons of thrust into pounds of thrust [or vice versa].)

    However, colloquially, people do use the kilogram as a weight. But your use of colloquial English in a scientific context has clearly puzzled or annoyed several of your readers.

  84. Nigel Depledge

    Jadehawk said:

    on a side note… why are newtons such an uneven measurement?! everything else in metric works out nicely in the decimal system, but not that one? (would probably explain why it’s never going to be popular)

    Because Newtons are not fundamentally derived, but depend on the force of gravity at the Earth’s surface. Earth’s surface gravity, not caring much for the SI, does not fit neatly in with any other SI units.

    Actually, come to think of it, the second and the metre are pretty arbitrary, too, but at least the rest of the SI is based on them (and, IIRC, on the Coulomb, which is also arbitrary).

  85. Nigel Depledge

    [pedant mose]
    The BA said:

    In fact, ich spreche ein bisschen Deutsche. Vielen Dank.

    Actually, Phil, that should be Deutsch.

    And don’t forget that foreign-language words and phrases expressed within English text should be italicised. ;-)

    [/pedant mode]

  86. Nigel Depledge

    Heh. I just noticed my typo in my most pedantic comment on Phil’s blog ever. That’ll teach me, I guess.

  87. Ibeechu

    @Nigel:
    Scientists (and, indeed, the Mythbusters) use Newtons a bunch, but when’s the last time you heard your friend tell you about how his sister had a baby weighing 40 Newtons? Or your mechanic telling you you should inflate your tires to 240000 Newtons per square meter (yeah, if your mechanic said that, he’d probably use Pascals, but let’s not split hairs.)

    I’m totally with Phil on this. It would be incredibly stupid to say that my mass is 180 pounds, because then you’re intentionally mixing mass with weight. But if you say that I weigh 81 and a half kilos, you’re using “kilos” to mean “the weight of an object with a mass of 1 kilo on Earth.” That’s too clunky to say in casual conversation.

    As an aside, next time I get a form that asks for my weight, I’m going to put 800 Newtons, and let them figure it out.

  88. jokergirl

    This sounds like something out of a Niven story. How about a gas planet with a mini neutron star in its core? (Yeah, I know, physics will be against me on that one, just thinking of alternate scenaios than the same density all the way through…)

    ;)

  89. Nigel Depledge

    Ibeechu said:

    @Nigel:
    Scientists (and, indeed, the Mythbusters) use Newtons a bunch, but when’s the last time you heard your friend tell you about how his sister had a baby weighing 40 Newtons? Or your mechanic telling you you should inflate your tires to 240000 Newtons per square meter (yeah, if your mechanic said that, he’d probably use Pascals, but let’s not split hairs.)

    I think I anticipated your objection, Ibeechu…

    I said:

    However, colloquially, people do use the kilogram as a weight. But your use of colloquial English in a scientific context has clearly puzzled or annoyed several of your readers.

    See?

  90. Ibeechu

    Aha, Nigel, I see :)

  91. Unspeakably Violent Jack

    Expressing weight in kilogrammes may be technically wrong but at least everyone can understand it!
    But pounds? Is 9000 pounds a lot?
    *Shrugs*

  92. How about a gas planet with a mini neutron star in its core?

    That would be much smaller than this object, which is pretty much the size we expect for a 21-Jupiter mass ball of hydrogen (Phil’s claim that this is “bizarre” notwithstanding – it’s only bizarre if you assume that things don’t get compressed at high pressures). Putting a heavy core at the centre would make the object even smaller, to get it back to the required size means making the envelope around the core less dense than hydrogen (good luck with that), and/or putting in an awful lot of extra heat in the object’s interior to puff the planet’s size up.

  93. lithiumdeuteride

    It’s filled with the super-dense substance known as ‘dark matter’, each pound of which weighs over ten thousand pounds…

  94. JohnW

    That was a very interesting link about planet migration.

    So extrasolar planets usually have these odd orbits, i.e. very close to the star and very eccentric?

  95. So extrasolar planets usually have these odd orbits, i.e. very close to the star and very eccentric?

    We certainly find a lot of them (I’m not sure if they’re in the majority anymore) with larger eccentricities than we’re used to for planets and a lot of them are closer to their stars than we expected. (The two actually anti-correlate a bit: the closest in planets seem to have the lowest eccentricities. This isn’t entirely shocking: tidal stresses probably circularize the orbits.) But there’s a selection bias at play there, too: it’s easier to find close in planets with eccentric orbits since you get bigger signals in the radial velocity searches.

  96. Obi-Wan

    Perhaps it’s the Death Star…

  97. Kol

    A friend pointed me at this article with the comment: “Denser than lead!”

    At first, I thought she was making a comment about someone’s intelligence level. It seemed like a rather insulting phrase at first blush but when I read the article, all was right with the world.

    Then I saw the strike-through and the footnote. That’s when I became confused.

    After reading the comments, I’m still not sure if she was making a reference to the planet in question or …

    Hey, AzO! :)

  98. Mighty Favog asked, “But I’d be interested to know if any real scientists have hypothesized such a planet as large and dense as COROT-exo-3b.” Check out Robert L. Forward’s hard SF book Dragon’s Egg (and subsequent Starquake). It’s not a planet, but a neutron star that supports life. A little OT, but I truly enjoyed these books and wanted to share. – g^2

    P.S. Based upon the extensive ‘discussion’ of weight v mass, I’m going to demand that all packages read “Net Wt 16 oz (4.44N)” (or whatever the relevant conversion is, of course).

  99. Yeah, that was rude – I’m sorry.

    D

  100. Linnet

    Thank you for a very interesting and just plain awesome article. As a member of the public at large, who, I’m fairly certain, your articles are geared towards, I would like to voice my appreciation for your use of terms that the average reader can relate to, although some unspeakably pedantic types feel the need to cleave to their own superior flaunting of terminological detail to show that they too are smart enough to have an enjoyable astronomy blog, but too cool to do so. …Or something, I honestly can’t find what point these guys are making, other than trying to show that they’re the smartest people on the internet.

    Oh, wait! Let me peruse your every word and comment reply one more time in case there’s some trivial typo to point out that hasn’t already been taken! Damn, I got nothin’.
    Thanks again, this is just so cool.

  101. Nigel Depledge

    Andy said:

    That would be much smaller than this object, which is pretty much the size we expect for a 21-Jupiter mass ball of hydrogen (Phil’s claim that this is “bizarre” notwithstanding – it’s only bizarre if you assume that things don’t get compressed at high pressures). Putting a heavy core at the centre would make the object even smaller, to get it back to the required size means making the envelope around the core less dense than hydrogen (good luck with that), and/or putting in an awful lot of extra heat in the object’s interior to puff the planet’s size up.

    Plus, also, a neutron star, in order to be a neutron star, has a minimum mass of about 3 Solar masses, so it would be, like, more than 200 times Jupiter’s mass.

  102. Nigel Depledge

    Lithiumdueteride said:

    It’s filled with the super-dense substance known as ‘dark matter’, each pound of which weighs over ten thousand pounds…

    Huh? Recursion error…!!!!

  103. Nigel Depledge

    Obi-wan said:

    Perhaps it’s the Death Star…

    It’s certainly no moon!

  104. Nigel Depledge

    ExGeekDogTrainer –

    Well, an Imperial pound (lb) is about 455 grammes, or 4.45 N, so that was pretty damn close, I’d say!

  105. Nigel Depledge

    Addendum – in the gravitational field at the Earth’s surface.

  106. Bill Nettles

    This is fascinating stuff. And I’m glad that I started thinking “brown dwarf” before I got to your section on that. BUT… you (Phil) said: but I don’t like this definition. You could have two objects that look precisely the same, yet one could be a planet and the other a BD, just because they formed in different ways. That strikes me as silly.

    Not any sillier than distinguishing between gamma rays (which originate ifrom nuclei), x-rays (which originate from atomic electron clouds or accelerating electrons), or annihilation photons (electron-positron). They’re all photons, they can overlap in energy, but we use different names depending on the origin, because the process of their creation is important.

  107. Ray

    MMMMM Maybe what we’re looking at is an artificial object. This may be a low scale Dyson sphere creation by ET’s, all I can say is WOW !!!! what a weird object.

  108. Joost

    If the planet’s diameter was determined by its transition across the surface of the star, can’t we also make some conclusions about the planet’s atmosphere (if there is any, that close the star)? I would have expected this to yield at least some information on the composition of the planet.

  109. Svlad Cjelli
  110. Roger Reynolds

    I’m going out on a limb here, but what if this object is not a “failed” star, but a stellar remnant, a black dwarf, which was an impetus for the formation of the system out of a dust cloud, yet for some reason did not become the kernel of its new companion star?

  111. Chuck

    Well, we know it’s not Gold, since it’s denser than lead.
    and we know ( by looking at the lack of the explosion ) we know it’s not Plutonium or Uranium, so it’s probably between those two limits.

    Case Solved.

    Any volunteers to go out and grab a chunk of it?

  112. sean

    ITS OVER NINE THOUSANDTH!!!!!!

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