Slashdot Mirror

← Back to Stories (view on slashdot.org)

Our Moon Could Become a Planet

Posted by ryuzaki0 on from the size-does-matter dept.

anthemaniac writes "Earth's moon is drifting away from us more than an inch every year. In a few billion years, if the system survives, the moon would be reclassified as a planet under the new IAU definition. You gotta wonder if the astronomers who dreamed this definition up had thought of that."

18 of 438 comments (clear)

  1. In a few billion years... by advocate_one · · Score: 4, Informative

    both the Earth and Moon will have been swallowed up by the Sun when it becomes a red giant...

    --
    Donald 'Duck' Dunn: We had a band powerful enough to turn goat piss into gasoline.
    1. Re:In a few billion years... by durgaprasad_j · · Score: 5, Informative

      In about 5 billion years, when the Sun is a red giant, it will be so large that it will consume Mercury and Venus. Models predict that the Sun will expand out to about 99% of the distance to the Earth's present orbit (1 astronomical unit, or AU). However by that time the orbit of the Earth will expand to about 1.7 AUs due to mass loss by the Sun. Our planet will thus escape envelopment. -- Reference http://en.wikipedia.org/wiki/Star

    2. Re:In a few billion years... by SamSim · · Score: 3, Informative

      Actually, probably not. Even where it is right now, Earth is almost on the boundary line between being swallowed and escaping (Venus is definitely gone, Mars definitely isn't). But as the Sun expands it will also become more luminous, which means the solar wind will increase. Over billions of years this will push Earth into a wider, safer orbit. It'll still get roasted to a crisp, but probably survive as a planet.

      --
      qntm.org
    3. Re:In a few billion years... by Anonymous Coward · · Score: 1, Informative

      As a supernova, the sun will eject massive ammount of MASS (this is why a sun of ~1 solar MASS will end up a white dwarf of ~0.2 solar masses, not a neutron star ~0.8 solar masses).

      As it loses MASS, the gravitational well the earth sits in will shallow and the stable orbit will be further out (the earth has more kinetic energy than a stable orbit at its' current distance will allow).

      Therefore, when the sun goes nova, the sun will be smaller and the earth further out.

    4. Re:In a few billion years... by SamSim · · Score: 2, Informative

      The Sun is about 25 times too small to go supernova. A red giant and a supernova are different things. Fusion requires progressively more heat as you get to heavier and heavier elements. A star like the Sun can only get to... well, it can get past hydrogen, and once the hydrogen is used up it can burn helium too, but I think it peters out somewhere around carbon. There's not enough mass and hence not enough pressure and hence not enough heat to burn anything beyond that. Whereas a very heavy star can burn elements right up to iron (beyond that, you get NO energy out, so no element beyond iron can be fused). They build up a non-fusable core of iron which gets bigger and bigger until it becomes so big that it itself collapses under gravity to form a neutron star (or possibly a black hole). At this point the entire rest of the star falls on top of the neutronium core and explodes - that's a supernova.

      --
      qntm.org
    5. Re:In a few billion years... by jonored · · Score: 2, Informative

      Right on the nose; the heavier elements are produced in the actual supernova, when there is so much energy flying around that the reactions can take place, absorbing all the energy they want, and can produce the really heavy elements. Yes, they don't produce much - but then, there are tiny amounts of most elements relative to the amount of hydrogen and helium in the universe - just look at this planet - a lot of it is iron, and most of the rest is stuff lighter than iron. Fission plants are releasing the long-stored energy of supernovae :)

  2. It'll last our time by MathFox · · Score: 4, Informative

    "The sun will turn in a red giant before the moon gets far enough away to be classified as a planet"

    --
    extern warranty;
    main()
    {
    (void)warranty;
    }
  3. Re:Gosh. How shocking. by Anonymous Coward · · Score: 5, Informative

    Wrong, wrong, wrong! Just RTFA. The moon does not have to escape the Earth's gravitational pull in order to be re-classified as a planet. The only thing that would be necessary (according to the new definition of a planet) is that the Moon moves further away from the Earth, just enough so that the barycenter of the Earth-Moon system is above the surface of the Earth. The Moon would still orbit the Earth. Obviously, the moderators who gave a +5 Insightful to your comment have not read the article either.

  4. Re:sea levels by Don_dumb · · Score: 4, Informative
    the farther away the moon is, the lower the seas
    Are you sure?
    It was my understanding that the moon affects the level of the tides, not the mean sea level, which is far more a product of the Earths gravity and dependant sea water pressure/density.

    and this should compensate for the ice melting.. although I always wonder what's the big deal, since icebergs are 90% submerged anyway, and ice takes more space than water (cause of the air bubbles)
    Yes all those scientists must have missed that one, eh?, I am glad there are informed people like you in world to set them straight.
    You are assuming that all the ice is in the seas, which it is NOT. A large amount sits on land in the form of Ice Shelves, there is enough to cover an entire contient (Antarctica) as well as most of Greenland and Canada, not to mention all the ice in Glaciers. As all this melts (and there is enough in Antarctia to contain 90% of the worlds fresh water) it wil flow into the sea and the sea level will rise, that is 'the big deal'.

    But don't worry I am sure Mr President will give you a big pay rise for that wonderfully dismissive comment on the effects of climate change.
    --
    If this were really happening, what would you think?
  5. Re:Fatal Flaw in IAU Definition by kalidasa · · Score: 3, Informative

    That's not how the definition works - if a coorbital body has the barycenter of its minor orbit with its companion body outside either body, it's a planet. If it is too small to ignite fusion and orbits a star, it's a planet, regardless of whether the barycenter of the planet-star system is inside the surface of the star.

  6. Re:What would its name be by Ant+P. · · Score: 2, Informative

    Or maybe he was using, I dunno, Latin?

  7. Which is fundamentally what this is about, right? by porkchop_d_clown · · Score: 2, Informative

    Semantics, I mean. The IAU is attempting to maintain a logically consistent definition for a technical term of art which, unfortunately has an overlapping but divergent meaning in the public's mind.

    This can happen a lot with scientific terms; psychiatric terms come to mind - "manic" and "psychotic" have technical definitions that are only vaguely related to what the public thinks those words mean...

    --
    Clear, Dark Skies
  8. from a personal communication from a guy at IAU by The+Other+Agent+Coop · · Score: 2, Informative

    "5. The IAU classifies objects based on their current properties. Specialists note that the Moon is receding from the Earth, and in a few billion years, the barycenter will reside in free space, outside the Earth. The IAU, at that time, can then reclassify the Moon as a 'planet.' "

  9. Re:Wait a minute... by lobotomir · · Score: 2, Informative

    This just in: "By measuring the abundance of several elements across the lunar surface, scientists can better constrain the contribution of material from the young Earth and its possible impactor to condense and form the Moon. Current models suggest that more came from the impactor than from Earth." Source:ESA

  10. Re:Do the math... by LiquidCoooled · · Score: 5, Informative

    Consider 2 bodies of equal mass seperated by a distance of X.
    The Centre of mass is right in the centre of the space between them.

    The distance X increases by 1 unit, does the centre of mass also increase by 1 unit?

    Adjust this equation to put it into earth/lunar context and you will understand why scientists don't just "google the math".

    --
    liqbase :: faster than paper
  11. Re:Sun or Earth? by 2short · · Score: 4, Informative

    "Of Time and Space and Other Things"

    Which was a collection of essays on various interesting science stuff, though I don't know if any of it was published seperately.

  12. Re:Sun or Earth? by 2short · · Score: 2, Informative

    But you would not. Every other moon in the solar system gives you a spirograph like thing. Earths moon produces a uniquely boring patern: more or less an elipse, just a bit wobbly. Other moons curve away from the sun as they circle around the far side of their planet. Our moon always curves toward the sun, just slightly less tightly. If there is a "double planet" in our solar system, it is clearly Earth-Moon, not Pluto-Charon.

  13. Re:Sun or Earth? by terevos · · Score: 2, Informative

    Did you guys not read about the barycenter of gravity? Read the AU's definition. http://www.iau2006.org/mirror/www.iau.org/NEWS.55. 0.html

    The Earth-Moon isn't a double planet because the barycenter of gravity is clearly within the earth's surface because the size of the Earth is so much bigger than the Moon.

    However, Pluto and Charon's barycenter of gravity is on the outside of Pluto's surface. That is why Pluto-Charon is a double planet, but not Earth-Moon. It's scientific, not arbitrary.