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Space Science

Rocky Planet Discovered 331

Fraser Cain writes "Astronomers have discovered a rocky, terrestrial planet orbiting a nearby star, Gliese 876. The planet has approximately 7.5 times the mass of the Earth, double its radius, and orbits its parent star once every two days. This is the most Earthlike extrasolar planet discovered so far." Reader Karthik Narayanaswami points out that "the planet was discovered by the famed Berkeley astronomer Geoff Marcy," and adds a link to the news release from Berkeley.
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Rocky Planet Discovered

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  • by Anonymous Coward on Monday June 13, 2005 @07:20PM (#12808249)
    Oh wait... you said Rocky Planet.
  • by metlin ( 258108 ) * on Monday June 13, 2005 @07:21PM (#12808264) Journal
    Here is the link to the Berkeley press release [berkeley.edu] and information on Berkeley astronomer Geoff Marcy [berkeley.edu].

    And oh, looks like Slashdot is continuing to mirror Boing Boing [boingboing.net].
    • And Fark. And CNN.com. And other news sources. The website is based on the principle that someone else writes an article and it gets blurbed and linked here, what do you expect?
      • Boing Boing and Fark are news aggregators, while CNN is more traditional news. The difference being that Boing Boing and Fark link to sites like CNN, while CNN pays for the Reuters and AP news feeds themselves. What makes Slashdot different is that they're prepetually a day behind everyone else. But I still stick with Slashdot because FARK can be a little risque for work at times and I can generally pretend that Slashdot is somewhat related to the work I do.
  • Re: (Score:2, Interesting)

    Comment removed based on user account deletion
    • Re:Heh (Score:3, Funny)

      by forceflow2 ( 843966 )
      The wobble method is nothing compared to the weeble method. Of course, this has severe consequences when the planets fall down.
    • light curve method (Score:3, Informative)

      by peter303 ( 12292 )
      An alternative method is to look for eclipses of the planet passing in from its stars. About 5% of the planets have been discovered this way. One estimate [nasa.gov] is about one in two hundred stars have suitable orientations and plantary systems for this method, if one could observe them long enough. A @hundred megapixel space probe called Kepler [nasa.gov] might be launched around 2008 to observe light curves of several hundred thousand stars for several years. This might find dozens of eclipsing planets plus understa
  • minimum mass (Score:3, Interesting)

    by rd4tech ( 711615 ) * on Monday June 13, 2005 @07:22PM (#12808269)
    The team measures a minimum mass for the planet of 5.9 Earth masses
    It seems that planet's gravity is quite big for "earthlike" planet. Is life possible at all under such gravity? Any examples?
    • by Anonymous Coward
      Is life possible at all under such gravity? Any examples?

      Well, there's the Klingons on Uranus.

    • Re:minimum mass (Score:3, Informative)

      The planet has approximately 7.5 times the mass of the Earth, double its radius, and orbits its parent star once every two days.

      g_newplanet = G(7.5M_Earth)/4(r_Earth^2), where g is the gravitational field strength and G is the gravitational constant. This is less than 2g_earth.

      Seems close enough for life. Although I'm not sure why a stronger gravitational field would necessarily be a huge constraint on the development of life.

      And to preempt the trolls, my little convenient formula is good enough. R

      • The correct formula [utk.edu] is Fg = G((m1*m2)/(r^2))

        Using Google to come up with necessary constants gives me:
        ((6.67300 × 10E-11) * (7.5 * 5.97200E24)) / ((2 * 12 756 300)^2)

        (I used a theoretical 1 kilogram test mass, at the planet's surface, to simplify things.) ...which Google says is approximately 45.92 N. A one kilogram mass on Earth should exert a downward force due to gravity of 9.8 N if I remember my physics classes correctly.

        So, call it about 4.7 times the gravity of Earth. Life? Possibly - but I
        • but I sure as hell wouldn't want to move there.

          A story on the housing market in the Gliese 876 system reported a slight rise in new housing starts, but the real news is the frenzy of speculation. According to the Gliese 876 Housing Market Letter, permits for new homes on the rocky planet and its Jupiter-like siblings "totaled 5,294,101 in April, down nearly 2 percent over the past 12 months."

          The sales are phenomenal. "New-home sales reached 4,886,393 in April, up 26.2 percent from 3,871,936 in April of l
        • Radius of Earth (Score:2, Informative)

          by Anonymous Coward
          ... is 6378.5 kilometers, not 12756.3 as you have above. The correct values for the force on a 1kg mass on the surface are:

          Earth: 9.785 N

          New planet: 18.366 N

          So the grandparent poster is correct, the surface gravity would be about 1.9 times that of Earth.
        • Parent is wrong (Score:5, Insightful)

          by p3d0 ( 42270 ) on Monday June 13, 2005 @11:28PM (#12809923)
          This is pretty simple. Surface gravity for spherically-symmetrical masses scales linearly with mass and inverse-square with radius. The mass makes gravity 7.5 times higher, while the radius would make it 4 times lower, for a total surface gravity of about 1.9G.
    • Re:minimum mass (Score:4, Informative)

      by nacturation ( 646836 ) <nacturation&gmail,com> on Monday June 13, 2005 @07:32PM (#12808361) Journal
      Is life possible at all under such gravity? Any examples?

      And where do you propose we find such examples? In space perhaps? :) But seriously, check out this article [umassmed.edu].
      • the article is great, thanks
      • Re:minimum mass (Score:3, Insightful)

        by Knara ( 9377 )
        Aren't there creatures living at far greater pressures in deep sea environments? Wouldn't that be similar to having creatures living at high gravities (leaving out the other ways the planet clearly isn't very "earthlike" for the moment).
    • by marat ( 180984 ) on Monday June 13, 2005 @07:35PM (#12808388) Homepage
      Gravity is only 1.8 from normal - I believe you can get used to it. Meanwhile surface is 3.2 times larger, so if it could be terraformed it will hold a lot of people from our overcrowded Earth.

      Of course I put many questions aside like how would they get there, does it have any continents, how sensitive processes like childbirth are to the gravity, does its atmosphere shield properly from radiation, isn't it too cold/hot there (although this can be fixed) etc etc...
    • Re:minimum mass (Score:3, Informative)

      by B.D.Mills ( 18626 )
      The gravity would be about twice Earth's.

      Of course life would be possible with that gravity. Microorganisms don't care particularly about gravity, and any multicellular life that might evolve would adapt to whatever the local conditions are.

      What would make life untenable would be a lack of liquid water. This world is very close to the star and would be tidally locked to the star. Unless there are deep ocean basins on the nightside to permit the water to cycle back, the water would eventually freeze out on
      • Polar zone... (Score:3, Interesting)

        by Goonie ( 8651 )
        The favourite possibility of sci-fi authors for life on planets like this is in the polar "twilight zones". It'd be a hard, hard life (the winds would be killer hot or cold) but life has been found on some pretty strange places on Earth...
    • Re:minimum mass (Score:2, Insightful)

      by rsynnott ( 886713 )
      Deep-sea life is under far greater pressure. But it's interesting in that this is the first rocky planet found, as far as I know.
    • There was once a science program which explored the variation in human physiques. They mentioned that on Earth, there was a limit of about 2 metres height for bipedal physiques due to the dangers of severe head injury simple due to tripping over and hitting something. Practical examples were people with thyroid problems. And having a thicker skull didn't really help because it just gave your head more momentum when falling.

      If you have N times as much gravity, anything human would probably have to be 2/N me
  • by aXis100 ( 690904 ) on Monday June 13, 2005 @07:22PM (#12808276)
    With a new year every two days, everyone would be broke buying birthday cakes.
  • by istartedi ( 132515 ) on Monday June 13, 2005 @07:24PM (#12808289) Journal

    The thing has gotta be mighty close to the star. Mercury orbits in 60 days, right? This thing may not be a gas giant, but it must totally bake on the sunny side, and aren't there going to be some horrendous tidal forces with an orbit that close? It probably has no shortage of volcanism. Hey! It's Vulcan, maybe... if it can hold an atmosphere without having the stellar wind blow it all away. Whatever, it can't be Earth-like.

    • by XanC ( 644172 )
      Hey! It's Vulcan, maybe...

      If it is, does that mean Spock mates once every 14 days?

    • Kinda seems like at that proximity to it's star, the entire planet must me molten... Volcano? Uh...
    • by chaotixx ( 563211 ) on Monday June 13, 2005 @07:34PM (#12808377)
      Its Earth-like because it is a rocky, rather than gaseous planet. Astronomers have to find new planets by detecting the wobble in the path of the star being orbited, which is caused by the orbiting planet. The bigger the planet, the bigger the wobble, so big gas giants were the first planets found. The fact that it completes an orbit in two days also helps as you don't need to collect years of data in order to see the wobble. So it's really not very Earth-like, but its the closest thing found so far, outside of our solar system.
      • There are many others: Pulsar timing, Astrometry, Gravitational microlensing, Transit method, Circumstellar disks, and ... Direct observation (courtesy of wikipedia [wikipedia.org]
        • by frankie ( 91710 )
          Except that out of those, only microlensing is likely to detect non-giant planets (orbiting non-pulsars) and it's based on random luck.

          In practical terms, if you want to find earthlike planets, you use the doppler method.
    • According to the article it's just 2,000,000 miles from its star which give it an orbital velocity of roughly 75 miles per *second*. That's more velocity than it took to put the Pioneer and Voyager probes on orbits that could leave our solar system altogether!
    • this has me thinking a little. I imagine extraterrestrial life will have different chemical composition than the primarily HCNO life that we see here. as such, stronger gravity or 'harsher' atmospheres aren't so much a theorectical obstacle. however, the complexity of the seasons provides an interesting situation for chemical evolution. with a 2 day year, the climate must oscillate with a high frequency (i'm not sure how drastic the change is on Gliese 876.) however, here we have a climate which changes wit
    • Maybe they mean local days, not earth days? Ie, it orbits at a regular old speed, and just turns really slowly?
  • All four seasons in one day (or two days actually)

    • Well, if you climb into space to the world where you live, you better be ready to beat a hasty retreat to the stars...because if this new planet's star starts burning and exploding, then the dust from this distant earth-like planet might just shower over everyone.

      I'd love to stay and chat, but I'd better be home soon.
  • Hey SETI (Score:5, Interesting)

    by grub ( 11606 ) <slashdot@grub.net> on Monday June 13, 2005 @07:29PM (#12808330) Homepage Journal

    which is only 15 light years away

    So why not send some radio traffic which would obviously not be of natural origins. Surely 30ish years isn't that long to wait for a reply? (assuming the place has lifeforms which developed radio...)
    • Re:Hey SETI (Score:5, Funny)

      by nacturation ( 646836 ) <nacturation&gmail,com> on Monday June 13, 2005 @07:39PM (#12808426) Journal
      They could send them CNN or Fox News. Surely those signals are as unnatural as any.
    • Why can't we at least build the Macross Fleet BEFORE purposely advertising our position to everybody under the sun? ...Sigh.
    • So why not send some radio traffic which would obviously not be of natural origins. Surely 30ish years isn't that long to wait for a reply? (assuming the place has lifeforms which developed radio...)

      Oh yeah, sure. a planet with 7.5 G's and 400 degrees celsius surface temperature, constantly hit by solar storms, ripping away any possible atmosphere and inundating it with harsh radiation. That place is more sterile than a grandmother's womb. Its only two frikkin million miles away from its sun! There's nothi

  • ...you would wonder if all the women were named Adrian.
  • dorsai :)
  • Maybe someday they'll find evidence of a planet that actually might resemble earth in some way. Other than the fact that it's made of rock and orbits a star, theres not really much we can do with it.

    If we'd spend less gazing at stars (at least in the optical range) and more to actually develope an inexpensive space route the public might show more intrest in space. LONG CHAIN THE NANO-TUBES
  • by Anonymous Coward
    Its always interesting when we find these new planets in other systems, but the wobble method is just not effective for finding an earthlike planet. For starters, have you ever noticed all the planets found have extremely quick orbits (1 year = 2 days) etc. And infact the longer their year is the bigger the planet is (because although the wobble doesn't occur as quickly it is more pronounced. If a planet were to have orbits similar to ours it would take nearly 2 years to see one wobble back and forth. S
    • by helioquake ( 841463 ) * on Monday June 13, 2005 @09:09PM (#12809037) Journal
      Instead of moderating you down, I'm just going to comment here...

      Yes, our Sun wobbles like that. Its wobble is done mostly by Jupiter, but the Earth contributes as much as +/- 3 meters/s, if I recall correctly. And for these guys, it's not impossible to detect such perturbations.

      That said, the wobble method (Dopper detection) is good for all sizes of planets. If it is not a single planetary system, that will show up in the radial velocity curve (like it does here..non sinosoidal curve, I mean).

      What you should be asking is this: how the hell do they know about the radius of the planet? The mass isn't too hard to determine (Kepler's law would tell you); but the radius isn't. Not in the accuracy claimed here (2 earth radius). Since I don't have an access to the article yet, it's hard for me to judge the accuracy of the radius value. Nontheless, that's where all of you should be pondering about, not about the wobble method.

      Amazing that FARK readers are pointing this out better than Slashdot readers...what did we go wrong?
      • I haven't actually read the article, but the radius is probably just based on extrapolating the mass with a similar density to our own rocky planets.

        You're just not going to find anything heavier than iron in any significant quantities. That's basic astrophysics.

        It's certainly possible that the composition of the planet will be different from our own, but not very likely. We're assuming that planetary formation follows the same two courses throughout the galaxy (rocky planets and gas giants), and that pro
        • If the radius is not directly/indirectly measured by the authors, then this finding is weak.

          If the radius had been determined by the rate of occultation, etc., then I would have believed that the rocky planet solution CAN indeed exist; but if the radius is assumed based on the assumption that the planet must be rocky, then I'm not sure how solid (or shall I say "unique" mathematically) this rocky interpretation is. Sure, astronomers can make the assumption that the cosmic abundance is more or less the same
        • If it were twice the Earth's radius, it would have 8 times the volume. Assuming similar composition, it would therefore have 8 times the mass. But the article said 7.5 times the mass, which would mean 1.957 times the earths radius. But typical of news articles, the numbers get rounded up to nice whole numbers everyone can enjoy.
    • Big planets make their suns wobble more, little planets make them wobble less, but they all have their own impact on the same body at the same time, which will generate a cumulative result.

      By observing the harmonics in the wobble for any star for long enough we should be able to determine how many bodies are orbiting it and their period. The only limitations on this are how long we observe for and how sensitive our equipment is at watching it.

      On a stellar scale, we "listen" to the details of wobble of

  • by Pinefresh ( 866806 ) <william,simpson&gmail,com> on Monday June 13, 2005 @07:37PM (#12808404)
    I am not an astronomer, but isn't mars more earthlike than that?
  • by VitrosChemistryAnaly ( 616952 ) on Monday June 13, 2005 @07:46PM (#12808479) Journal
    Adrian!!!
  • by VernonNemitz ( 581327 ) on Monday June 13, 2005 @07:47PM (#12808489) Journal
    Seems to me that this is the core of one of those too-close Jovian types, and not a started-out-that-size planet.
  • Orbital Velocity? (Score:3, Interesting)

    by Doc Ruby ( 173196 ) on Monday June 13, 2005 @07:48PM (#12808494) Homepage Journal
    This planet's "year" is two Earth days. But how large is its orbital radius (other than "so close to the star's surface")? So, how fast is its orbital velocity? Is it so fast that the centripetal "force" (illusion) of its orbit is significant, compared to its (greater than Earth) gravity?

    In fact, even Earth seems like it should have centripetal effects. We rotate 1000MPH; we're orbiting at something like 70,000MPH, right? Shouldn't Earth gravity be balanced by detectable acceleration along the tangents to those circular motions?
    • in the article, it says it's about 2 million miles away from the star... that's .02 AUs...
    • by StupendousMan ( 69768 ) on Monday June 13, 2005 @08:09PM (#12808655) Homepage

      No.

      A body moving in a circle of radius R at a uniform speed V experiences an acceleration a = (V*V)/R towards the center of the circle. In neither of the cases you mention does any centripetal acceleration come close to the local gravitational acceleration at the surface of the planet.

      Case 1: The Earth: orbital speed V = 30 km/s, and R = 150 million km, so (V*V)/R is of order (10^8)/(10^11) m/s^2, or about 10^(-3) m/s^2. The local gravitational acceleration is about 10 m/s^2, of course. If you speak of the Earth's rotational motion at the equator, then very roughly V = 500 m/s and R = 6,400,000 m, so (V*V)/R has magnitude roughly (2.5 x 10^5) / 6.4 x 10^6 = 0.03 m/s^2; again, much less than 10 m/s^2 due to the gravitational pull of the Earth.

      Case 2: The new planet. Its orbital radius is about 2 billion meters, so the circumference is about 7 billion meters; if it travels that distance in a period of 2 days = 170,000 seconds, then it speed is about V = 40,000 m/s. The orbital centripetal acceleration is therefore of order (16 x 10^8)/(2 x 10^9) = 0.8 m/s^2. That's much larger than the Earth's orbital centripetal acceleration, but still far less than the likely gravitational acceleration at the surface (or cloudtops) of this planet.

      • Case 2: The new planet. Its orbital radius is about 2 billion meters, so the circumference is about 7 billion meters; if it travels that distance in a period of 2 days = 170,000 seconds, then it speed is about V = 40,000 m/s. The orbital centripetal acceleration is therefore of order (16 x 10^8)/(2 x 10^9) = 0.8 m/s^2. That's much larger than the Earth's orbital centripetal acceleration, but still far less than the likely gravitational acceleration at the surface (or cloudtops) of this planet.

        But this is
      • Note, on the other hand, that .03 is a significant effect if you've memorized 9.803 m/s^2. For that matter, things effectively weighing .3% more at the poles is responsible for sealevel at the poles being 21km closer to the center of the earth than it is on the equator.
    • Re:Orbital Velocity? (Score:2, Informative)

      by mazarin5 ( 309432 )
      Shouldn't Earth gravity be balanced by detectable acceleration along the tangents to those circular motions?

      It is, that's why we haven't flung off into the void, or been dragged into the Sun.

      Also, we really can't judge what it's semimajor axis is unless we know how massive the star is, but if we know that, then we also have the velocity.
      (6.67e-11)*M=(v^2)(r)
      where M is the mass of the star.

      Also, the centripetal force has a magnitude of v^2/r.

      HTH

    • I *think* I see what you're asking, and the answer is no (more or less).

      If the earth suddenly disappeared, we would all remain in orbit around the sun. See what I mean?

      I'm sure the force differentials you're talking about would be detectable, but only by sensative equpment.

      That is if I understood what you're asking...
    • No, the earth, and everything on it, is in constant freefall relative to the sun. We therefore feel no centripedal acceleration. Kind of like how astronauts are weightless when orbiting the earth.
  • by Edmund Blackadder ( 559735 ) on Monday June 13, 2005 @07:49PM (#12808512)
    After reading the article it seems like they "discovered" the planet simply by observing the star and two very large jupiter type gas giants that are circling the star. By the orbits of the planets and the "wobble" of the star they have determined that there must be another planet of the specified size and orbit.

    So essentially this planet was discovered solely on observation of its gravitational effect on other planets. In other words the scientists built a computer model which includes the star and two visible gas giants, and found a planet which they could insert in it so it causes the star and the gas giants to behave as they in the model as they do in observation. Then they declared that they have discovered a new planet.

    How did they know it was a rocky planet? Well, correct me if i am wrong but it seems like they decided that by elimination -- the planet is too small to be a gas giant and too close to the star to have anu liquid water on it. Therefore, it must be a rocky planet.

    Admittedly I do not know much about modern astronomy but all of this is a little troubling. I mean should we not obtain direct observation from something before we proclaim it "discovered"?

    I am sure modeling solar objects is very useful but modeling is limited to our current knowledge. If rely too much on modeling we will never discover anything that we do not already know about.
    • As with any other science, astronomers claim a discovery when the available evidence indicates the "discovery" is more likely right than wrong. Exactly when that happens is subject to some personal judgement. Some scientists are more conservative than others. Some have wound up with egg on their faces after announcing a "discovery" prematurely. Some discoveries are quietly, or even noisily, disputed for years after they are announced. Some widely accepted "laws of nature" are found to be subtly incorre
    • Agreed. We didn't discover much of anything here. We hypothisised that by a stars wobble there maybe a planet orbiting a star. Infact, if you read the aritcle it's full of conjecture and theory. Which is fine. They may be right, they may not be. But they didn't discover a rocky planet, let alone can say with 100% certainty that a planet is even there.
    • The majority of scientists consider the 'wobble' to be an effect of the planet(s) revolving around the star. If you don't accept that planets are the most probable cause, then what your best guess as to what is the cause of the 'wobble'? If you're answer is "I don't know, but they don't know either.", then I think you simply don't know enough to be critical of these PhDs who have made this discovery. (But then again, this is Slashdot, right?).

      I think you over-simplify your estimation of how they decided i

  • by rd4tech ( 711615 ) * on Monday June 13, 2005 @07:55PM (#12808557)
    do not try to pick up fight with the natives ...
  • Whatever (Score:5, Funny)

    by iamdrscience ( 541136 ) on Monday June 13, 2005 @08:19PM (#12808732) Homepage
    Tell me when they find the Bullwinkle planet. Bullwinkle was always funnier.
  • by Siergen ( 607001 ) on Monday June 13, 2005 @08:20PM (#12808743)
    Th other extrasolar planets that have been discovered so far have much greater masses (as measured by the wobble they induce in their parent stars). However, although the articles I have read so far described these planets as gas giants, I have never seen any explanation by the astronomers as to why they are are certain these planets are gaseous, and not rocky.

    Is there some physical reason why massive rocky planets cannot form, or are we assuming that massive planets in other solar systems must resemble massive planets in our solar system?

  • ...with slightly lower surface temperatures, as this one ranges from 200 to 400 degrees, obviously uninhabitable. If they could locate one that closely mirrors the earth as far as environmental and atmospheric conditions, then we could start focusing on how to start migrating humans via cryogenic and hyperspace travel to said planet. Would solve earth overpopulation problems.
  • by richardoz ( 529837 ) * on Monday June 13, 2005 @08:54PM (#12808971) Homepage
    I can hear it screaming now...

  • Wasn't another rocky extrasolar planet discovered [cnn.com] last August, orbiting Gliese 436?

    Why are we constantly finding these rocky planets orbiting M-Class red dwarf stars? Is there some correlation? (Possibly, these are the aged, burnt-out cores of old gas giants whose gassy layers have been blown off by their parent star?) Or is this the only type of star being surveyed for rocky planets?
  • Krypton? (Score:3, Interesting)

    by brownpau ( 639342 ) on Monday June 13, 2005 @09:33PM (#12809245) Homepage
    It's a massive rocky extrasolar planet, with much higher gravity than Earth's, orbiting extremely close to its parent star, an M-class red dwarf -- A RED SUN.

    Sound familiar? Perhaps, even, super?
  • No possible life? (Score:3, Informative)

    by slavemowgli ( 585321 ) on Monday June 13, 2005 @09:53PM (#12809394) Homepage

    From TFA:

    [...] its temperature probably tops 400 to 750 degrees Fahrenheit (200 to 400 degrees Celsius)--oven-like temperatures far too hot for life as we know it.

    Um, no, that's not true - there certainly are bacteria which can survive these temperatures and have adapted to them (those living near hydrothermal vents at the bottom of the ocean, for example). Whether this new planet could (even theoretically) host life is another question entirely, of course, but the statement that we do not know life that can endure such temperatures is simply not true.

  • by tooth ( 111958 )
    Frow TFA: Now, for the first time, we have evidence for a rocky planet around a normal star.

    Apart from the one we're standing on? :)

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