A tiny wobble reveals a massive planet

By Phil Plait | May 29, 2009 7:00 am

For the first time ever, an extrasolar planet has been detected due to its physically slinging around its parent star.

Artist’s concept of VB10b
Artiost’s impression of the planet orbiting VB10. Image credit: NASA/JPL-Caltech

Imagine two children, one big and one small, facing each other and holding hands. They swing around each other, each making a circle. The bigger kid makes a smaller circle, and the smaller kid makes a larger circle. If you stand off to the side, you’ll see each child alternately approaching and receding from you as they make their circles on the ground.

In effect, this is how we’ve been finding most of the planets orbiting other stars. As a planet orbits its parent star it tugs on that star gravitationally, and we see a very slight Doppler shift in the light of that star as it approaches and recedes from us.

If only we could magnify the system hugely, then we would actually see the star make a little circle as the planet orbited it. Well, this new discovery did just that!

The star is called VB10, and lies about 20 light years away. That’s close! Only a handful of stars are closer. It’s a very small, faint star: classified as an M8 dwarf, it’s barely massive enough to maintain the pressure and temperature in its core needed to fuse hydrogen into helium. If it were any less massive it would be a brown dwarf, a starlike object that is not actively fusing elements in its core.

The planet is massive, about six times the mass of Jupiter. All of these things together — the close distance, the low mass of the star, and the high mass of the planet — combined happily for this discovery. The massive planet tugs on its star, which is low mass so it makes a relatively big circle, and the nearby location makes it easier to see that motion.

Astronomers watched the system very carefully for 12 years. As the star was swung around by the planet, the physical motion was seen as a wobble in the location of the star. The position of the star had to be measured with exacting precision, which ain’t easy. Even a slight warp in the detector itself can throw off the measurements, as can a hundred other possible errors. I’ve done work like this myself — not exactly like this, but trying to get very high-precision positions on a detector — and it’s frustratingly difficult. This discovery is an amazing achievement.

Size of the planet around VB10
Comparison chart of the sizes
of the star and planet.
Click to embiggen.

And the system itself is pretty interesting. For one thing, although the star is far more massive than the planet, physically they are about the same size! When a planet gets to be about as massive as Jupiter, its size remains the same as mass is added to it; instead of getting bigger it gets denser. So if you took two Jupiters and smashed them together, you’d get one planet with twice the mass and twice the density, but about the same size as the original planets.

The star is very dense, so even though it’s much more massive than its planet, they are about the same size. That would have to look pretty weird if you were there.

VB10b, the planet, orbits the star pretty close in, about 50 million km (30 million miles) out… closer than Mercury orbits the Sun! The star is so dim, though, that the planet would only be about room temperature at its cloud tops. It’s possible there are other, less massive planets closer in yet, though I doubt it. The gravity of the super-Jupiter would probably disrupt their orbits.

As it happens, VB 10 is a flare star; it sometimes erupts in ginormous X-ray flares so violent we can detect them here on Earth, 200 trillion kilometers away! So any planet orbiting that star would be cooked to a crisp. It’s ironic that such dim bulbs can produce such enormous blasts of energy, but the eruptions are magnetic in nature, much like the Sun’s own solar flares. These kinds of stars can have powerful magnetic fields, capable of much violence.

Perhaps the most remarkable thing about this system is that VB10 is the lowest mass star known to have a planet. It may keep that record for some time; there aren’t too many stars with a lower mass, or else they wouldn’t be stars at all!

So no mater how you look at this, it’s a pretty cool discovery. And it adds another arrow in our quiver of methods to detect other planets. It’s a difficult one to be sure, and it takes a lot of patience, but now we know it works.

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (51)

  1. Jeff

    The really neat stuff will be when Kepler results get rolled out. They’ll find at least a thousand planets similar in mass to earth around sun-like G type stars

  2. Gary Ansorge

    Sounds like a perfect thesis for a PhD,,,speaking of PhDs,,,

    Stumbled across this comic strip from Stanford. Good thing woos don’t know how truly geeky we really are,,,

    http://www.phdcomics.com/comics/archive_list.php

    Does this remind you of your trials, Phil???

    GAry 7

  3. QUASAR

    How many Earth-like planets do you think that we’ll find with Kepler?

    I will be astonished if we find 4 or 5!

  4. T_U_T

    Just wonder how long those flares last, and how much energy they have. And, also, how often they happen.
    .
    I mean, if they happen only a few times a year, and are short enough, they would be not dangerous. Just every living being would have to stay in their burrows for a few hours, but nothing bad would happen.

  5. Typo in last paragraph, first sentence: “So no mater matter…”

  6. StevoR

    Awesome discovery! Congrats to the discoverers & thanks to the BA for posting on this. 8)

    The BA :

    The gravity of the super-Jupiter would probably disrupt their orbits.

    Or maybe just lock them into a resonance set up like that for Gliese 879 and many other exoplanetary systems?

    that VB10 is the lowest mass star known to have a planet. It may keep that record for some time; there aren’t too many stars with a lower mass, or else they wouldn’t be stars at all!

    Or is it? What about the brown dwarf that had an exoplanet photopgraphed around it back in 2005~ish 2 M 1207 A?

    VB = Van Biesbroeck right? If I recall right, wasn’t there an early planetary or brown dwarf candidate (later found to be a false alarm) around VB -8 back inthe early to mid 1980’s?

    @ QUASAR : Can you define what you mean by Earth-like please?

    Note that Venus has been described as “Earth’s twin” – and so it is in mass and diameter – & yet because of its location and thick carbon dioxide atmosphere Venus is anything but what I’d consider truly like Earth! ;-)

    Also we’ve already found three planets that are only about three times Earth’s mass around a pulsar and COROT Exo7b (name?) which is only 1.7 (?) Earth mass .. & to stretch a point further there’s Gliese 581 c (another superVenus?) too whicxh has been descibed as “Earth’s sister” (in the media at least!) Do they fit in anyone’s idea of Earth-like or not? How strictly like Earth does a planet need to be to qualify?

  7. IVAN3MAN

    Phil, er… in the first line, it should be: “… an extrasolar planet has been detected due to [it] physically slinging around its parent star.”

    Also, in the last paragraph, first line, it should be matter, not “mater” — which is British slang for mother. :-)

    Edited to add: I now see that Todd W. has mentioned that matter, too.

    Man, I have to learn to type faster! :|

  8. Ryan

    Is it possible for planets to form without stars in nebula or is the gravitational attraction of a star necessary to produce a planetary system?

  9. @IVAN3MAN

    Giving you competition. :)

    As to the it/its bit, he could either change “its” to “it” or “physically” to “physical” to make the sentence grammatically correct. Just throwing another option out there.

  10. QUASAR

    @ StevoR

    With an atmosphere, temperatures and sizes similar to the Earth’s!

    And with life on it too, of course, not intelligent but primitive!

  11. Dense Charlie

    So, both the star and the planet are about the size of Jupiter? How can a star be so small as a planet? And how can the star be denser than a very heavy planet, but still be a ball of gas? I must be missing something.

  12. StevoRaine

    For reference, comparison and contrasting purposes :

    From my personal catalogue of exoplanets compiled from various sources incl.this blog & various astronomy magazines, books and websites :

    2M 1207b : The first exoplanet photographed – in 2004 on April 27th – by a European-American team using the Yepun telescope in Chile – although contending claims exist. It has 5 Jupiter masses and orbits 55 AU from a brown dwarf of 25 Jupiter masses. This exoplanet or brown dwarf’s name in full is actually 2 MASSW J1207334-393254 b! This system is a member of the TW Hydrae association of stars all about 8 million years old.

    NB. The smallest confirmed exoplanet record holder if you count brown dwarfs as stars.

    PSR B 1620-26 b, “Methuselah” or “Genesis”* planet : The oldest exoplanet and second to orbit a pulsar, it is located inside the globular cluster M4 orbiting a tight pulsar-white dwarf binary. The superjovian planet has the lowest mass but largest diameter in that system versus the Earth-sized white dwarf and city-sized pulsar! The Genesis planet* has an estimated age of 12.7 billion years old.

    NB. A case where a planet is actually larger albeit far less massive than both its “stars” !

    CoRoT-Exo-7 b : The smallest exoplanet in mass yet found around a normal main-seqeunce star (rather than a pulsar!) which also rejoices in the unprouncable catalogue name of TYCH 4799-1733-1 b. This transiting exoplanet has a radius of 1.7 x Earth’s and takes just 20 and a half *hours* to circle its K0 orange dwarf sun making it also the record holder for the shortest orbital period and distance! Its discovery was announced on Feb. 3rd 2009 having been discovered by the CoRoT space observatory. The mass of CoRoT exo-7 b is somewhere within a range of 11 to 2 Earth masses.
    ( Pages 26 – 29, “The First Earth-Sized Exoplanet” by Brandon Tingley in Australian Sky & Telescope’ magazine, May-June 2009)

    NB. Previously HAT-P-11 b (yes, the “name” is for real folks) was the smallest known transisting exoplanet. Don’t ask me its mass/radius as my source doesn’t say .. :-(

    Not that any of these comparions take anything away from this latest marvellous find
    Now I’m adding this remarkable new exoplanetary discovery to this wonderfully growing and diversifying catalogue of new found worlds! :-D

    ———-
    *No, NOT that ‘Genesis planet’ from Star Treks II, III & IV!

    I <3 loves <3 my exoplanets I do! ;-)

  13. StevoR

    @ QUASAR – Okay that is a tough ask – and a good definition of truly Earth-like! THX. :-)

    It has frequently occured to me a lot before that several planets described in the media (and even sometimes by people who should know better) as being “Earth-like” or “Super-Earth’s” (eg. Gliese 581 c) are, in fact, much more like Supersized & Superheated versions of Venus than anything like Earth.

    Plus I’m not sure whether we really know – or have even come close to accurately imagining – what a 5 or so earth-mass planet is really like …

    We have no solar system analogues making speculation by analogy and theory potentially misleading albeit intrinsically fascinating and probably irresitable! ;-)

  14. Clive DuPort

    How big are the BA’s hands?
    Only a “handful” of stars within 20 light-years of Earth?
    He must have well insulated oven mitts to hold them!

  15. IVAN3MAN

    Ryan:

    Is it possible for planets to form without stars in nebula or is the gravitational attraction of a star necessary to produce a planetary system?

    According to Wikipedia, a rogue planet (also known as an interstellar planet, free-floating planet or orphan planet) is an object which has equivalent mass to a planet and is not gravitationally bound to any star, and that therefore moves through space as an independent object. Several astronomers claim to have detected such objects (for example,
    Cha 110913-773444), but those detections remain unconfirmed pending visitation.

    Some astronomers refer to these objects as “planets”, usually because they believe such objects were planets that were ejected from orbit around a star. However, others believe that the definition of ‘planet’ should depend on current observable state, and not origin. Additionally, these objects may form on their own through gas cloud collapse similar to star formation; in which case they would never have been planets.

  16. Clive DuPort

    IVAN3MAN, A lumpy thing that isn’t a star flying through free space will still be orbiting something, albeit a galaxy or a number of galaxies, even the whole universe. The orbit may not be circular, oval or any sort of regular shape & may even include straight lines sometimes. Even a straight line is the circumference of a very big circle. There are probably many objects like that out there although I assume their number would reduce as they are captured by the gravity of various stars.

  17. I wonder why “VB10b”. What happened to “VB10a”?

  18. Wow… Todd W. and IVAN3MAN just beating up poor BA with their pedantic, nit-picky spelling and grammatical corrections. How bush-league! Just totally uncalled for and I for one am appalled!

    Oh… and by the way, what the heck is an “Artiost’s Impression”, BA? ;-)

  19. StevoR-Correcting

    … Or rather adding & refreshing peoples memories in this case for those who may be curious again from my personal exoplanets catalogue :

    Gliese 876 : The first red dwarf discovered to have planets, Gliese 876, located 15 light years off in Aquarius, boasts three worlds. The first known pair of Gl-876’s planets were soon found to be in a protective 2 :1 resonance pattern dating back to early in the systems formation and arguing for a slow gentle migration process rather than chaotic gravitational interaction forming the system. The inner of those pair weighs in at ½ Jupiter’s mass and orbits in 30 days while the outer has nearly twice Jove’s mass and orbits in 60 days. A third lower mass planet was discovered in 2005 and was the smallest found to that date. Hailed as possibly the first rocky world having just 7 Earth-masses and orbiting in 2 days at the searingly close distance of 2 million miles from its star, this “luciferean” exoplanets estimated temperature ranges from 200-400 degrees Celsius.

    NB. Was there another member of this exoplanetary system discovered later? Think there may have been … Or was it in this next system??? (GL-581)

    Gliese 581 : This system was much hyped for the recent discovery of the Gliese 581c,which had the lowest mass – five earth’s – exoplanet to then which was found in 2007(?). It was proclaimed by some that the middle lower mass planet in this three planet system was “Earth’s big sister” and the first possibly habitable planet discovered – but a few notes of caution need sounding : Firstly we simply don’t really know what a 5-earth-mass planet is likely to be like. It could possibly be more like a mini-Neptune or a totally water-covered or exotic “hot (high pressure) ice” world rather than anything remotely like Earth. Secondly, re-examination of likely conditions make it seem the original optimistic estimate of Gliese 581c’s likely temperatures was way-off with the most likely scenario being more akin to a higher gravity version of Venus than Earth. Then we’ve got to take into account the problem of largely past flare activity, tidal locking, lesser metallicity and a number of other such things … That said the discovery of Gliese 581c is still a positive sign and well worth further investigation! The system also backs up the trend for low-mass stars to have generally low mass planets with Gliese 581, a real average M3 red dwarf star located 20.5 ly off – & positioned right next to Beta Librae (Zubeneschmali) in our skies – which seems stable and has lower than solar metallicity boasting three confirmed exoplanets – an innermost 15 earth-mass Hot Neptune orbiting in 5 days, our famed five-earth mass probable Super-Venus orbiting in a day short of a fortnight and an outer 8 earth-mass extrasolar planet that may be a slightly better – though still dubious – bet for potential habitability orbiting in 84 of our days. This indication that low mass worlds are common especially around the most common type of star is perhaps the strongest bit of good news to come from the discovery and bodes well for future even better habitable planet candidates.

    OGLE-05-390 L b or “Hoth” : A small and – quite probably – rocky 5-earth mass exoplanet that was discovered around 2005 by microlensing circling a red dwarf 21,000 ly distant – the furthest known exoplanet. It’s “year” is our decade! (10 year orbit.) This was (one of) the very first rocky “Super-Earth” (more like Super-Mars? Or Super-Pluto even?) planets to be discovered.

    Gliese 436 b : One of the first exoNeptunes or Hot Neptunes this is also the first known “Hot Ice” type planet – composed largely of layers of exotic high pressure, high temperature forms of water ice. Gliese or GJ-436 b is a 25 earth mass extrasolar planet circling a 33 light years away M2 dwarf star every two and a half days. Through Gl-436 b transiting its sun, astronomers have been able to measure its diameter at about 50,000 km wide suggesting it is neither gaseous like Jupiter (too small) nor rocky like Earth (too big) and thus models suggest a mainly watery composition. Its surface temperature is about 380 degrees but underneath a dense, steamy atmosphere, high pressure forces this vast layer of water – well above the usual boiling point into exotic types of ice. Celsius and under high pressure and temperatures hot ice is likely to be the result beneath a dense atmosphere.

    Nb. Not to be confused with another Gliese star -Gliese 581 – & note too that ‘Gliese’ is sometimes variously abbreiviated Gl, Gl or GJ. (C’mon, IAU lets give these significant stars and exoplanets proper names hey!?)

    Also note for COROT-Exo-7b which has only twice the diameter of the Earth or a diameter of about 25,000 kilometers or so that the surface temperature of the planet must be well over 1000 C.

    & for the record here’s some

    ***
    record-holding & historic exoplanets :

    (d. = discovered)

    First ever & first pulsar planets– PSR B 1257+12, d. 1991 4 exoplanets

    First sun-like star & Hot Jupiter – 51 Pegasi, d. 1995

    First Binary star with exoplanet – 16 Cygni d. 199?

    Nearest star with exoplanet – Epsilon Eridani 10.5 ly (But claimed for Lalande 21185, 8 ly)

    Brightest star with exoplanet – Pollux just over Fomalhaut, 17th & 18th brightest app. mag stars!

    Most exoplanets – 55 Cancris a.k.a. Rho-1 Cancris, five planets

    Oldest & only so far in Globular cluster – PSR B 1620-26 b in Messier 4 globular near Antares.

    Most massive & only so far in Open cluster – Ain or Epsilon Tauri, Hyades 2.7 solar masses, a G9 yellow giant star.

    Smallest exoplanet for sunlike star – COROT-Exo-7 b 2 x Earth diameter (mass =?)

    Most eccentrically orbiting exoplanet – HD 80606 b “Icarus planet / Comet orbit Planet”

    Planet with the most Suns – HD 188753 b or “Tatooine” , triple star system, three orange dwarfs

    (So far as I know, these “record holders” are correct & up to date – please let me know if any are wrong or outdated.)

  20. Chris A.

    @Jeff:

    Err…IIRC Kepler is expected to find around 40 Earth-mass planets, not thousands. Perhaps you’re thinking of how many planets it may find in toto (including those considerably more massive).

  21. StevoR-Correcting

    @ # 17. ioresult :

    I wonder why “VB10b”. What happened to “VB10a”?

    Well A or ‘a’ is always the star, planet letters start at b; eg. Gliese 581 a is the systems primary “sun”, b is the first planet discovered around it (NOT necessarily the closest) c is the next exoplanet discovered and so forth.

    @ # 14. Clive DuPort : (May 29th, 2009 at 8:37 am)

    How big are the BA’s hands? Only a “handful” of stars within 20 light-years of Earth?
    He must have well insulated oven mitts to hold them!

    Crikey! & I thought *I* took things too literally! ;-)

    As for straight lines being ‘orbits’ or ‘circles’ … Hmm … Not so sure there. In Riemannian (sp./name?) geometry maybe, NOT in Euclidean terms. Personally, (& hey, maybe I’m wrong) I’d call a straight line trajectory a flight path rather than an orbit. If something orbits something else, then in my mind, it needs to revolve around it – doesn’t it? (/puzzled/?)

    Finally, @ IVAN3MAN #6 :

    Also, in the last paragraph, first line, it should be matter, not “mater” — which is British slang for mother.

    Not that it really matters but isn’t ‘Mater’ Latin or maybe German for mother? I’m not sure but have the feeling it is – anyone? ;-)

    PS. @ Celtic_Evolution # 18 : Oh… and by the way, what the heck is an “Artiost’s Impression”, BA?

    I think its what you get after allowing for “Artiostic license” regarding typos! ;-)

  22. Robert T.

    Hi Phil, I am very fortunate to have stumbled upon your blog. Thank you for these informative lectures which have reignited my interest in science, particularly that of astronomy.

    I have a question here that I’ve been mulling over for some time now. What happens to matter that get sucked into a black hole? Does it add to the mass of the black hole and increase its gravitational pull?

  23. Mike

    Not sure I see the significance of this alternate way to discover planets. Is it more sensitive than Doppler for close stars? For small stars?

  24. IVAN3MAN

    Clive DuPort, I never stated that a rogue planet is not orbiting the galactic centre, and neither does the Wikipedia article that I have linked to; it basically states: a rogue planet is an object which has equivalent mass to a planet and is not gravitationally bound to any star, and therefore moves through space as an independent object — around the galactic centre, if you will.

  25. BJN

    Since I watched a Science Channel show about using this technique to find planets, it’s hard to believe that this is news. In fact, isn’t astrometry the technique used in the first confirmed extrasolar planet discovery way back in 1995? Or is “radial velocity” not an astrometric measurement?

    http://en.wikipedia.org/wiki/Extrasolar_planets

  26. DrFlimmer

    @ StevoR-…

    Not that it really matters but isn’t ‘Mater’ Latin or maybe German for mother? I’m not sure but have the feeling it is – anyone? ;-)

    At least it is not German. That would be “Mutter”. Could be Latin, but I never had Latin in school, so I must pass the solution to this problem on to another one…

    @ Mike

    Not sure I see the significance of this alternate way to discover planets. Is it more sensitive than Doppler for close stars?

    No, but Doppler only works well when the planet orbits mostly in the plane “parallel” to the line of sight. only then it is possible to see the motion of the star in the spectrum. If the orbit of the planet is perpendicular to the l-o-s the star moves only “up and down and to the left and to the right”, but not towards or away from you – so one cannot measure any Doppler motion; but if the star is close enough you can detect the motion itself. And that is what happend here.

    Hm… I guess this explanation is not the best one…. hopefully I’ve helped at least a bit ;)

    @ Robert T

    What happens to matter that get sucked into a black hole? Does it add to the mass of the black hole and increase its gravitational pull?

    Simle answer: Yes.

  27. StevoR –

    Six years of Latin School… /shudder/

    Yeah… mater is indeed Latin for “mother”.

  28. Ryan

    @Mike
    This planet was discovered because of its Doppler effect on the star.

  29. Mike

    @Dr.Flimmer
    Of course! {slaps forehead with palm} Thank you.

  30. Mike

    @Ryan – No, it wasn’t. It was detected by the star’s changing position in the sky. That’s the point.

  31. amphiox

    Room temperature at its cloud tops? This means habitable zone, doesn’t it? Would that also mean room temperature on the surface of any large moons?

  32. Mater matters:
    from a Latin/English dictionary online (the interwebs is SO kewl!)

    # genetrix : mother.
    # mater matris : mother.

    Pasco ergo sum
    (I browse, therefore I am)

    J/P=?

    (After 11 3/4 years of Catholic School, one would think I would know/remember this)

  33. Mapnut

    Speaking of the artiost’s impression, that’s an impossible view of course. The planet and the star are shown the same size, but in the same field of view. Even at the same distance as Mercury, if the planet looked that big, the star would have to be a bright dot.

    I wasn’t going to post that, but this has turned into a nitpicking party, so why not? :)

  34. Ryan

    @Mapnut
    No, the planet and star are only 1.5 times their diameter apart. Lol.

  35. @Jeff: The really neat stuff will be when Kepler results get rolled out. They’ll find at least a thousand planets similar in mass to earth around sun-like G type stars

    The numbers I have seen are about 1000 planets total (i.e. of all sizes), and around 50 Earth-like planets.

    If all of the 100,000 target stars have Earth-like planets in orbit around them, then Kepler would expect to find 500 of them, so if they find 50, that would mean approximately 10% of the stars have Earth-like planets. I have no idea whether the theorists are being conservative in their guestimate of 50, but I hope it turns out that they are!

  36. Porky Pine

    I’m confused. I thought that this method was the typical method of finding extra-solar planets. How did we find all the other ones?

  37. Torbjörn Larsson, OM

    Cool! New method, smallest star, Earth analog system (in scale).

    And it must be an awesome sight with a planet as large as the sun!

    Not sure I see the significance of this alternate way to discover planets. Is it more sensitive than Doppler for close stars? For small stars?

    Good question. IIRC the press release points out that this system would scale up to an Earth analog (in mass, I believe, if the habitable zone is at this planet). I.e. earlier techniques have preferentially caught Jupiters close to the star.

    They hope to see more of these Earth analog systems this way.

  38. Torbjörn Larsson, OM

    I’d call a straight line trajectory a flight path rather than an orbit.

    I believe a physicist would call it a trajectory whatever derivatives it has. Likewise, it was my impression that for astronomers every trajectory is an orbit; however I might easily be wrong.

    That would make some sense however, since most any object out there would travel under the influence of a gravity gradient – from stars, from galaxies, or from clusters. Similarly to how Hyperion have a “rotation” albeit it is a chaotic one so it have no closed revolution.

  39. I’m confused. I thought that this method was the typical method of finding extra-solar planets. How did we find all the other ones?

    Porky Pine, astrometry—the method used here—detects extremely small changes in a star’s position as a planet (or planets) moves in orbit around them. The other technique you are probably confusing this with is the “radial velocity” or “Doppler” method which detects extremely small variations in speed away from and towards Earth (i.e. measuring the Doppler shift of the star’s light).

    In both cases the presence of the exoplanet is revealed by its (very small) effect on the star it is in orbit around. The Doppler method has been and continues to be a more sensitive method for finding exoplanets which is why it has already found hundreds of them, but it works best when the orbit of a planet is edge-on in relation to Earth. Since astrometry looks for changes in the star’s position, I would assume that it will be better at detecting exoplanets with orbits at 90 degrees to Earth (like looking down on a dinner plate). So the two methods should complement each other very well in the future.

  40. George E Martin

    @39 tacitus said:

    Since astrometry looks for changes in the star’s position, I would assume that it will be better at detecting exoplanets with orbits at 90 degrees to Earth (like looking down on a dinner plate). So the two methods should complement each other very well in the future.

    No, I don’t think so. What’s being measured is the change of position on the sky of the primary. In this case it would not make a difference what the orbital inclination of secondary to the primary is in our line of sight. The primary’s position will still be seen to wobble.

    The underlying technique used is old. In essence what was found was an astrometric binary. (There are astrometric binaries in the plate collection of UVA’s McCormick telescope.) It’s just that the mass of the secondary is much less than previously discovered astrometric binaries. That’s due to the new instrumentation used in this case which is what is novel.

    Astrometric measurements with optical interferometers will likely find many more of these.

    George

  41. George E Martin

    When I wrote the above I meant, but forgot, to say that the astrometric technique traditionally requires objects to be close. Phil mentions that VB10 is about 20 light years away. Putting it another way, it is about 6 parsecs away, and the parsec is a more appropriate unit of distance than light year in this case.

    By definition, a star one parsec away has a trigometric parallax of one second of arc. VB10 would have a parallax of about 0.17 seconds of arc (rounding). That’s a difficult angle to measure. The change in VB10’s position due to the orbit of VB10b would likely be in the sub milli arc second range given the stated mass for VB10b.

    Thus, for traditional astrometric techniques, a star really has to be close to detect planets via astrometry . Using interferometry to do the astrometry will push the distance much farther away.

    George

  42. StevoR

    @ # @7 Celtic Evolution, # 32 John Paradox & #26Dr Flimmer :

    Re Mater = latin for mother (not german) THX. :-)

    @ # 38. Torbjörn Larsson, OM Says:

    I believe a physicist would call it a trajectory whatever derivatives it has. Likewise, it was my impression that for astronomers every trajectory is an orbit; …

    What if its on the ground,within an atmosphere or just a line on paper or computer screen? ;-) Still thanks for that.

    @ # 31. amphiox :
    Room temperature at its cloud tops? This means habitable zone, doesn’t it? Would that also mean room temperature on the surface of any large moons?

    I’m not sure but I got the impression that the room-temperature here comes about because of the infra-red heat generated by VB-10 b the planet itself. So any hypothetical moons ( may not be at room-temperature but possibly much colder – and perhaps also, breifly, much hotter during flare outbursts from VB-10 a, its sun.

    Another question is – would the closer gravity of the star make these hypoothetical moons less likely? Again I’m not sure but seems possible. :-(

    Of course, the other problem here is that at the cloud tops there is NO solid surface. This is a superJovian planet with an ultra-thick atmosphere with any solid core (whether molten lava, hydrocarbon tar or diamond a la Jupiter) presumably being wrapped in a huge mantle of metallic hydrogen, under a sea of liquid pressurised gases under an unfathomable tower of Hydrogen- Helium & impurities “air.”

    There are speculations in many SF novels (eg. ‘Space Odyssey 2010′, etc .. by Arthur C.Clarke) about alien life floating in such Jovian and, I suppose by extension, Superjovian planetary clouds but … who knows? ;-)

    Incidentally, much the same applies to the gas giants in our solar system and other “cold Jupiters” elsewhere. These planets all radiate stacks of heat and have at least some regions at room-temperatures albiet very high pressures. These could just concievably be habitable if you can imagine floating ecologies which are of course highly speculative – there is also the likley lack of sunlight for some if them* and the problem of what nutrients are possible as food…

    “Hot Jupiters”, OTOH, are, well incredibly hot, sometimes approaching the temperatures of the outer surface layers of their red or brown dwarf stars in the 1,000 + degrees Celcsius range stellar making life there, seem even more improbable. Not than anything can be ruled out entirely but.. :-(

    * How deep do you think sunlight penetrates from the cloudtops down into the atmospheres of such Jovian & Superjovian planets? Starlight diminishes, pressure rises and things get pretty tough quickly I’d guess. Of course this doesn’t apply to VB-10 b where the room-temp zone is at the cloud tops so .. Interesting idea but one with a few obstacles.

    Another thought occurs to me too – as gas cools it liquifies then freezes. Over time Jupiter and the other gas giants, Superjovians and even Brown Dwarfs will cool off.

    1) Will they ever freeze over into solid balls of frozen gas?
    2) How long might this take?
    &
    3) What would such an old cold Jupiter be like?

    Anyone?

  43. MadScientist

    @Gary: I’d say it’s an awful topic for a PhD – who wants to slave away for 12 years to get the data needed to publish? Although coming up with a clever experimental design might be worth a PhD, I wouldn’t want any students tackling jobs that would take so long to get results. I’d say find something which can be done in under 6 years (preferably under 4), get it done, and move on or expand the work after getting the degree.

  44. George, of course you are correct. Thanks for the clarification.

  45. planetguy

    Here’s a couple of answers to various questions. Radial velocity measures the Doppler shifts of stars. That was the technique used in 1995 and for about 300 other planet finds. Astrometry measures the position of the star. That is completely different and that is why the inclination angle of the orbit is measured with astrometry but not radial velocity. Also a good separation between stars-brown dwarfs-and planets is mass. A star has to be at least 70 Jupiter masses. A planet has to be below 13 Jupiter masses.

  46. Thomas Kilgour

    Question:
    Could we use the transit method to look for a planet like this? Since its size is so close to the size of it’s star and it’s orbit is so small would it significantly change the amount of light we see? Do we even know if this planet transits its star from our perspective?

  47. Mike G

    Maybe a dumb question, but I’ve never seen it answered before, so I’ll ask it here. With this method of detection I always hear that the star has one planet, not 2 or 3 or 8… How can you distinguish? Is the resolution on the wobble really sharp enough to distinguish multiple forces acting on the star?

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