Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?
Moon Space Science

Earth May Once Have Had Multiple Moons 186

fyc writes "A new study from NASA's Ames Research Center has suggested that the collision of Earth and a Mars-sized object that created the Moon may also have resulted in the creation of tiny moonlets on Earth's Lagrangian points. 'Once captured, the Trojan satellites likely remained in their orbits for up to 100 million years, Lissauer and co-author John Chambers of the Carnegie Institution of Washington say. Then, gravitational tugs from the planets would have triggered changes in the Earth's orbit, ultimately causing the moons to become unmoored and drift away or crash into the Moon or Earth.'" The longest-lasting of such Trojans could have persisted for a billion years. They would have been a few tens of kilometers in diameter and would have appeared in the sky like bright stars.
This discussion has been archived. No new comments can be posted.

Earth May Once Have Had Multiple Moons

Comments Filter:
  • by Taint Bearer ( 957479 ) on Wednesday May 07, 2008 @06:09AM (#23321914)
    Setting Suns. Not moons.
  • Re:Not far fetched. (Score:5, Informative)

    by mpe ( 36238 ) on Wednesday May 07, 2008 @07:09AM (#23322162)
    Doesn't sound too far fetched since Earth has Cruithne sharing it's orbit, which in it's own way is a "second moon".

    Except that this object isn't sharing the Earth's obit at all. It's in a solar orbit which is similar to the Earth's. In order to call something a "moon" of the Earth it would need to be orbiting the Earth.
  • Mod Parent Clueless (Score:5, Informative)

    by Anonymous Coward on Wednesday May 07, 2008 @07:28AM (#23322256)
    Dude, there are hundreds, if not thousands of Pluto sized planetoids. Pluto was discovered first of those objects, and mistakenly thought to be very unique.

    Planets are the huge and few main satellites of the sun. It's a category defined entirely by scarcity. There are only 8. Not 8000. Pluto can't be a planet and the hundreds or thousands of larger objects not be, but the fact that there were thousands of similar objects wasn't discovered until after Pluto was added to the planet list. It's just an act of intellectual honesty to note that Pluto is only unique historically for being seen early. But now we know: It's not a major satellite sufficient to be in the planet category. You call this arbitrary, but it's as unarbitrary as anything could be.

    What the hell does this have to do with how big a moon is? Any object orbiting a planet is automatically a satellite, any satellite that is naturally occurring is automatically a moon (by some definitions, anyway). Perhaps you should invest in a good dictionary. They are free on the internet.

    Thank goodness we don't have to rely on your inane concepts of 'fairness' in celestial bodies for our language needs.
  • by clonan ( 64380 ) on Wednesday May 07, 2008 @08:20AM (#23322550)
    The biggest difference is the mass ratio's between the satellite and it's parent (this goes for planets as well as moons).

    If the mass of the satellites starts to approach the mass of the parent then the system will become unstable. The Moon is by far the largest satellite as a percentage of mass anywhere in the solar system. The Pluto-Charon system beats the Earth and Moon but Pluto was downgraded from a planet. For the earth-moon system, the center of mass for the system is still inside the earth. The Pluto-Charon system the center of mass is roughly 1/3 of the way to Charon. The only reason it is stable is because it is so far away.

    If the moon was significantly larger (or there was an additional moon of significant size) they system would become unstable and tend to lose satellites until it WAS stable.

    Jupiter's moons are so much lighter that Jupiter has an iron gravitational grip on them. Short of a major external disruption (say getting hit by another moon) all of Jupiter's moons are staying put.
  • by KlomDark ( 6370 ) on Wednesday May 07, 2008 @09:46AM (#23323252) Homepage Journal
    They discovered Cruithne [messagebase.net], orbiting the Earth in a weird 770 year orbit, back around 1999.
  • Re:Any observers? (Score:3, Informative)

    by Chris Burke ( 6130 ) on Wednesday May 07, 2008 @11:36AM (#23324382) Homepage
    would have appeared in the sky like bright stars.

    Appeared to whom?

    Nobody. One of the first things you learn in astronomy (observation, not education) is how to distinguish between a star and a planet or moon. It's easy: stars twinkle, big balls of rock or gas don't. Next time you're out at night, try to find Venus (it's the brightest object after the moon and sun), and compare it to any bright stars in the sky like Polaris. Venus will look very static, like it's just a dot of paint on the sky. Long before anyone knew what the solar system looked like, or what a 'planet' was, people knew that the planets were "different" than the stars.

    BTW you can see the 4 largest moons of Jupiter through a decent pair of binoculars; they too don't look like stars.
  • by Chris Burke ( 6130 ) on Wednesday May 07, 2008 @12:21PM (#23325190) Homepage
    I must've missed the part where we found HUNDREDS of objects the size of Pluto. Seems to me we've only found two or three so far.

    A few more than that are known [wikipedia.org]. Theoretically there are probably many more such objects, and very unlikely for there to be earth-sized objects.

    There are more than eight planets. Pluto is a plant. Xena (or whatever official name they've assigned it) is a planet. Get over it.

    No, Pluto is just a large Kuiper belt object, a glorified asteroid. You are the one who must get over it.

    Or has science devolved to the point where we just change the definitions to give us the answers we want, rather than looking at the evidence and following it to where it leads?

    You're the one who wants to include Pluto as a planet based on... what? History? Sense of style? Desire for there to be more planets? They changed the definition of planet to exclude Pluto based on the evidence of discovering that there was an entire belt of objects at that distance including other objects in Pluto's orbit, and it was not in fact unique or formed in the same way as the other planets. The only reason it was ever called a planet in the first place is because we didn't know about the Kuiper belt or all the other objects of similar size. In what bizarre universe is refusing to revisit old assumptions made out of ignorance "looking at the evidence"? That's stasis. Science is all about revising theories.

    Why not call every asteroid in the asteroid belt and Kuiper belt planets? There'd be tons of planets then. There's several objects in the asteroid belt that are similar size to Pluto. I don't hear you calling them planets. But that's because the not-following-evidence accusation you level at science is the one you yourself are guilty of.
  • by clonan ( 64380 ) on Wednesday May 07, 2008 @12:26PM (#23325308)
    Actually, size doesn't directly have anyhting to do with being designated a planet.

    The official deffinition of a planet is:

    The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:
    (1) A "planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

    (2) A "dwarf planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

    (3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".


    1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
    2 An IAU process will be established to assign borderline objects into either "dwarf planet" and other categories.
    3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

    While a body of insufficient size will not "overcome rigids body forces" or have "cleared the neighbourhood around its orbit" the deffinition doesn't state that it must be at least 2000 km in diameter (which is arbitrary and was a running contender for the deffinition of planet). Infact you could have a very dense but small object (smaller than pluto) meet the deffinition of planet and a very defuse but large object (larger than the earth) NOT meet the deffinition. While size and mass are important, they are not what define a planet.

    Since pluto hasn't cleared it's local neighborhood, it is not a planet. In addition, hundreds of pluto sized object HAVE been found in the oort cloud and Kupier Belt. However when a similar object was found orbiting inside Neuptune (Eris I beleive) it only accelerated the redeffinition of planet that was already underway.

    This deffinition is actually pretty reasonable based on what types of objects dominate a solar system (excluding the sun) and how they are formed. If you look at the history of where this new deffinition came from you will find that the "devolved" scientists almost made an exception for Pluto but in the end decided to

    look(ing) at the evidence and following it to where it leads
  • by bearbones ( 532127 ) on Wednesday May 07, 2008 @12:51PM (#23325876)


    lagrangian points require two bodies

    what was the second body creating the points while the moon was being formed?

  • by Anonymous Coward on Wednesday May 07, 2008 @03:15PM (#23328188)
    First, Cruithne does not orbit the Earth but the Sun with the period very similar to Earth so this 770 years is just the difference when one laps the other. Second - when the Cruithne will lap the Earth, due to the proximity the Earth will change Cruithne's orbit and period - it will slow it down so that Cruithne will be failing behind from that moment and the Earth will get the lap back in about 380 ears. So your 770 years "period" lasts only for that 770 years - how can you call this one-time quantity a period? Third, it was not discovered in 1999 but in 1986.
    How could any moderate the parent informative? Maybe because there in not a -1 misleading option?

"I shall expect a chemical cure for psychopathic behavior by 10 A.M. tomorrow, or I'll have your guts for spaghetti." -- a comic panel by Cotham