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Science Where are the other moons of Earth?
Science Where are the other moons of Earth? | Where are the other moons of Earth? |
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| by William Atkins | |
| Friday, 16 May 2008 | |
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Page 2 of 2 The collision of the Earth with an object the size of the planet Mars probably produced many small moonlets. They probably orbited about the Earth for millions of years. The research team theorizes that the moonlets stayed in the vicinity of Earth until the gravitational force from other planets pulled them away. They probably either crashed into the Earth or Moon, or drifted away from the two bodies. Lissauer states, “The perturbations from the other planets are very, very tiny. But they change the shape of Earth's orbit, which changes the effect that the Sun's gravity has on the moons…. [That] is what ultimately destabilizes the Trojans.” [New Scientist] Thus, they conjecture that there should be more moons around Earth than just one (the Moon), however they were destroyed earlier in the evolution of the solar system when they crashed into the Earth or Moon, or were ejected off into the solar system. In the end, only the Moon was left to orbit our planet. The article published as the result of this NASA study appears in the May 2008 issue of the journal Icarus under the title “Solar and planetary destabilization of the Earth–Moon triangular Lagrangian points.” The abstract to their paper states, “In the restricted circular three-body problem, two massive bodies travel on circular orbits about their mutual center of mass and gravitationally perturb the motion of a massless particle. The triangular Lagrange points, L4 and L5, form equilateral triangles with the two massive bodies and lie in their orbital plane.” “Provided the primary is at least 27 times as massive as the secondary, orbits near L4 and L5 can remain close to these locations indefinitely. More than 2200 cataloged asteroids librate about the L4 and L5 points of the Sun–Jupiter system, and five bodies have been discovered around the L4 point of the Sun–Neptune system. Small satellites have also been found librating about the L4 and L5 points of two of Saturn's moons.” “However, no objects have been discovered around the Earth–Moon L4 and L5 points. Using numerical integrations, we show that orbits near the Earth–Moon L4 and L5 points can survive for over a billion years even when solar perturbations are included, but the further addition of the far smaller perturbations from other planets destabilize these orbits within several million years. Thus, the lack of observed objects in these regions cannot be used as a constraint on Solar System formation, nor on the tidal evolution of the Moon's orbit.”
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