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Space Science

Terrestrial (Rocky) Planet Discovered 70

KilgoryTrout writes "A 'super-Earth' planet was identified in orbit around mu Arae, a star 50 light years away. It orbits at 2 AUs and surface gravity is 14gs. Two gas giants have been detected in orbit about the star. Space.com's article suggests that it is a failed gas giant's rocky core."
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Terrestrial (Rocky) Planet Discovered

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  • Umm (Score:2, Funny)

    by MindStalker ( 22827 )
    No planet so small has ever been detected around a normal star.

    Ummm Mercury, Venus..??
    Shrugs.
  • Another... (Score:2, Funny)

    by cs02rm0 ( 654673 )
    ...person with their 4" piece out?
  • by krinsh ( 94283 ) on Wednesday August 25, 2004 @02:51PM (#10071101)
    It may take a couple hundred years to get there; but there's bound to be a group of people eager to go on a long-term mission to this place - bring some kids along and make sure things are mixed up enough so the babies aren't West Virginians after a generation or three - and report back when they get there.

    I know it's a lot more complicated than that, but we should. (and I'm from WVa so I'm not really being mean)
  • by hoggoth ( 414195 ) on Wednesday August 25, 2004 @02:57PM (#10071156) Journal
    This is very interesting, however it isn't the most "Earthlike" planet found yet. There are three planets [space.com] generally ignored by scientists because they are dead and orbit a neutron star. However they are Earth sized and there is a possibility that in the distant past they may have harbored life.

    It would be monumental to find evidence that life on Earth isn't a singleton freak accident, even if we found it on worlds that could never harbor life again.

  • If the star in question is roughly equal to our sun and the planet is 2AU away from the sun (which is twice the distance the earth is from the sun) why would it be so hot?
  • 2AU? (Score:4, Informative)

    by thhamm ( 764787 ) on Wednesday August 25, 2004 @03:04PM (#10071235)
    found a bit more here:

    http://www.eso.org/outreach/press-rel/pr-2004/pr-2 2-04.html

    cant find anything about the 2AU. is that possible? 2AU radius and 10day period?
  • Wrong numbers (Score:5, Informative)

    by Euphonious Coward ( 189818 ) on Wednesday August 25, 2004 @03:05PM (#10071241)
    It says the super-earth is so close to its star that it orbits in 10 days. A nearby gas giant is orbiting at 2 AU. Also, they say the mass is 14 times that of Earth. That would imply a surface gravity of 14G only if it was the same size as
    Earth, which could only happen if it were made out of uranium or something.

    I guess a radius 2.4 times that of Earth, if it's made of the same stuff, or less if it has more iron and less silicates.
    • Re:Wrong numbers (Score:4, Informative)

      by Euphonious Coward ( 189818 ) on Wednesday August 25, 2004 @03:14PM (#10071339)
      Assuming radius is 14 ** (1/3) = 2.41 times Earth's, and it's made of the same materials, then surface gravity should be 14 / (2.4 ** 2) = 2.41G also.

      Probably it's denser, and radius is smaller, and surface gravity is higher, maybe 3 or 4G, but not 14G.
      • is it at all possible to measure the "size" (density?) at such a distance?

        i thought, these wobble/transit methods are used to just time the orbital period, so you can derive, using the stars mass, the companions mass?
        • by Engineer-Poet ( 795260 ) on Wednesday August 25, 2004 @03:40PM (#10071576) Homepage Journal
          It goes something like this:
          1. The star's temperature yields its luminosity, and indirectly its mass.
          2. The Doppler shift and period of the wobble yields the planet's mass as a fraction of the star.
          3. The amount of light blocked by the planet yields its area, and thus its size.
          4. From size, you can calculate volume. Density = mass/volume.
          If the star is close enough and the planet heavy enough you can cross-check the wobble using astrometry.
      • by Engineer-Poet ( 795260 ) on Wednesday August 25, 2004 @03:32PM (#10071501) Homepage Journal
        The average density of Earth is about 5.5 g/cc, while the surface rocks average 3.5 g/cc. There are two reasons for this:
        1. The Earth's core is made largely of iron, which is much denser than rock.
        2. The core matter is compressed by the pressure of the overlying material.
        If you took Earth and doubled its size with no other changes, you'd have a surface gravity of about 2 G. If you tripled the diameter of the core at the expense of the mantle (more metals in the star, more metals in the planet), you'd increase the density of the mantle zone from ~4 g/cc to 8-10 g/cc; this would give you 6-9 G at the surface. Factor in some additional compression due to the overlying mass, and I could see 14 G surface gravity.

        Still doesn't hold a candle to Mesklin.

        • OK, if its density is doubled -- i.e., it's all nickel-iron -- then radius is halved, and gravitation squared, you'd get ~9G. There's no way you'd get enough extra compression to bump the gravity to 14G. (Remember the iron in Earth's core is under great pressure already.) You would need to admix uranium or something, as I noted earlier.

          Under normal pressures, U is a little more than twice as dense as Fe, and might be a little more compressible; figure 2.5. Then, you get 9 * 2.5 * 2.5 = 56G for a solid

          • First, you assume that the material is nickel-iron. It could be mostly osmium for all you know.

            Second, if you double the density, the radius doesn't necessarily change. Which means that instead of 1 kg/m^3 of material you have 2 kg/m^3 of material. Which in turn means that the gravitational acceleration will double. As in a_gravity/m1 = G * M_planet / radius_planet^2. The radius doesn't change, G is a constant, but M_planet is twice as much. Thus you have twice as much acceleration.

            If most of th
            • It could be mostly osmium for all you know.

              No it couldn't. Curve of binding energy peaks at element 26 (Fe); osmium is up at atomic number 76. Osmium is always going to be too rare to make whole planets, as you noted.

              ... you can't compress uranium much more than it already is.

              Au contraire, compression is one of the ways that very sub-critical masses of fissionables are turned into bombs (neutron reflectors are another). Peak densities are several times the STP solid density. [google.com] Perhaps you never wondered

              • Au contraire, compression is one of the ways that very sub-critical masses of fissionables are turned into bombs (neutron reflectors are another). Peak densities are several times the STP solid density. [google.com] Perhaps you never wondered why implosion designs are used for nuclear weapons; that's one reason.

                Exactly the reason you'd not see a planet made of the stuff. Your cross-sections are just too high; meaning your chances of a neutron escaping one atom and hitting another that much more likely.
                • Iron isn't fissionable. Neither is nickel. Try again.
                  • au contrare...

                    Anything except hydrogen is fissionable. It's just that your energy approaches infinity as you try to do fission on elements on the hydrogen-iron curve. Iron is indeed fissionable, it just takes more energy to split it than you would get out.
                    • Here's what I was replying to, in case you missed it:

                      Exactly the reason you'd not see a planet made of the stuff. Your cross-sections are just too high; meaning your chances of a neutron escaping one atom and hitting another that much more likely. Once you get past a certain mass, you've created a bomb.

                      Regardless of bombardment, iron does not emit neutrons with enough additional energy to cause a chain reaction (which you admitted when pressed), so your statement in the great-grandparent is simply not re

                    • I was replying to this person..

                      OK, if its density is doubled -- i.e., it's all nickel-iron -- then radius is halved, and gravitation squared, you'd get ~9G. There's no way you'd get enough extra compression to bump the gravity to 14G. (Remember the iron in Earth's core is under great pressure already.) You would need to admix uranium or something, as I noted earlier. Under normal pressures, U is a little more than twice as dense as Fe, and might be a little more compressible; figure 2.5. Then, you get 9
                    • You know far too much about nukular explosions to be a normal, God-fearing American. You must be a terrorist.

                      Guards! GUARDS!!! HOMELAND SECURITY ALERT!

                      So I was under the impression that the reason we have a hot, molten core is that the radioactive elements inside it are causing a sustained fission reaction that's generating the heat. I'm guessing what you just said means that's not entirely accurate? I.E., if the threshold ("critical mass," if I understand the term correctly) for a fission reacti
                    • As we currently understand atomic physics, that would be the case.

                      The ratio of iron to fissionable elements is pretty big; in other words, there is much more iron than fissionable materials.

                      Much of the initial heating of the earth was from compression of the stuff that the planet is made of. Most of that heat was trapped inside, and allowed the most common, dense materials to slowly sink to the center. Because of pressure, the core is believed to be a semi-solid oblong sphere of iron and nickel, wit
            • Boy, I bet there'd be some great fishin' on that planet. ... ::runs::
          • Oops, I'm wrong. Double the density, and the volume goes down by half, so the radius goes down by just 1/(2**(1/3)), or just 0.79. Surface gravity increases, then, by a factor of 1/(0.79**2), or 1.59, for a total of just 2.41*1.59 = 3.8G. There's no way a 14-Earth-mass planet can pull much more than 4G surface gravity if the heaviest stuff you have to work with is iron, no matter how hard your little planet's gravity squeezes it.

            So, your uranium planet (for as long as it would last) would be (1/(2.5**(

        • Should we automatically assume that this planet 14 times the mass of the Earth will be denser than the Earth?

          If you look at the density of the planets in our solar system [adlerplanetarium.org] you will see that the smaller rocky planets are more dense than the more massive planets.

          Most of the Universe is Hydrogen. Hydrogen is very light. That means that hydrogen molecules move more quickly.

          It is like Maxwell's daemon. Some of the hydrogen at the edge of the planet's atmosphere will be slower than average, and some will

    • Ok, here's the math:

      g = GM/R^2

      g = gravitational acceleration (m/s^2)
      G = Universal gravitation = 6.67*10^-11 m^3/kg/s^2
      M = mass (kg)
      R = radius (m)

      So, we are told that the new planet has 14 times the mass of the earth. If we were also to assume that the person who submitted this article is correct and that the gravitational acceleration is 14 times that of the Earth ("14 Gs") [I assume he/she/it meant at the surface of the planet], then we have the following equation for the radius of the newly discovered
      • Dammit! Dammit! I missed some important numbers in the density calculation. volume of sphere = R^3*Pi*4/3, not R^3. Duh! Ok, so the density is not 3.2x10^5 kg/m^3, but is instead, 3*3.2x10^5/(Pi*4) =~ 8000 kg/m^3. Like iron. Earth, of course, is around 5.6x10^3 kg/m^3. I'm an idiot!
  • by RobertB-DC ( 622190 ) * on Wednesday August 25, 2004 @04:27PM (#10072009) Homepage Journal
    While researchers do not know the full range of conditions under which life can survive, the newly discovered world, with its hot surface, is not the sort of place biologists would expect to find life as we know it.

    No, of course not. Life there would posess super-human strength [wikipedia.org] as an adaptation to the enormous gravity. Were inhabitants of this planet to visit Earth, they would be faster than a speeding bullet, and stronger than a locomotive. I wager they'd be able to jump tall buildings with a single bound.

    I wonder if anyone's thought of a name [wikipedia.org] for this planet?

    (How can there be two dozen comments, but nobody made this connection yet?)
    • Uh, it can't be Krypton. Krypton has already been destroyed. Still, it would be interesting to know what the core of the planet is made of!
    • I wonder if anyone's thought of a name for this planet? (...) Life there would posess super-human strength as an adaptation to the enormous gravity. Were inhabitants of this planet to visit Earth, they would be faster than a speeding bullet, and stronger than a locomotive. I wager they'd be able to jump tall buildings with a single bound.

      So since Krypton is already taken and any proposal on /. is bound to pay tribute to the home computer era of the 1980s, from your description of the life forms and their

  • Located at only 0.09 AUs from the star (less than one fourth of Mercury's orbital distance in the Solar System), the planet competes an orbit in less than 9.55 +/- 0.03 days and may have a surface temperature of 1,160 Fahrenheit (or 900 Kevin).
    The astronomers believe that under the most likely planetary developmental scenario of inner migration from around 3 AUs under the influence of outer giant planet "b" now at 1.5 AUs, this planet is likely to have an "essentially rocky core" with an atmosphere of five
  • by DesScorp ( 410532 ) <DesScorp@GmERDOSail.com minus math_god> on Wednesday August 25, 2004 @06:06PM (#10072868) Homepage Journal
    Come on, I love Astronomy, but observation is the only method to gather information outside of our solar system in astronomy (well, except for radiation studies), and this "world" is so far away, how the hell do they know it's a gas giant core? We're talking about extreme conjecture here. No photos, no probes, just some evidence that it exists by means of tracking positions of its' star (that's typically how these far-away planets are "found"; observations of SOMETHING pulling agaisnt a star and affecting it's motion).

    • I was also always under the impression a gas giant has no solid core. Am I wrong in my assumption?
      • Gas giants are supposed to have rocky cores, yeah. It's just that most of the planets volume is gas, usually under heavy pressure. So any probe would be crushed and melted long before it had a chance to get to a core.

        Keep in mind what I said about conjecture here. The idea that the gas giants have rocky cores just fits the best theories that astronomers have. There's no way to actually bore down and tell for sure at this time.
  • Density has alot to do with the magnitude of surface gravity. It could be that if this was a core then this "planet" has no mantle/core but is just one big rock with no layers at all. That should "up" the surface gravity considerably.
    • ". . . is just one big rock with no layers at all"

      That's not very likely. The gravitational potential energy that would be converted to heat as the planet accreted would be more than enough to melt the entire body, thus allowing the heavier materials to tend to sink to the center of the planet. A planet this size would almost certainly have differentiated.

      Besides, it is mass and radius^2 that matter, not specifically density. For example, Jupiter has a bulk density around 1330 kg/m^3 (water is 1000 kg/

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