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.
Re:More proof of the Gospels (Score:5, Informative)
Re:Not far fetched. (Score:5, Informative)
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)
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.
It's all about the mass! (Score:5, Informative)
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.
Don't forget Earth's other moon - Cruithne (Score:4, Informative)
Re:Any observers? (Score:3, Informative)
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.
Re:Maybe you are right... (Score:3, Informative)
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.
Re:Maybe you are right... (Score:5, Informative)
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".
Footnotes:
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
Re:Not an especially unique theory. (Score:2, Informative)
insightful?
lagrangian points require two bodies
what was the second body creating the points while the moon was being formed?
Re:Don't forget Earth's other moon - Cruithne (Score:1, Informative)
How could any moderate the parent informative? Maybe because there in not a -1 misleading option?