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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 1 of 2 A mathematical model developed by American scientists Jack Lissauer, of NASA’s Ames Research Center (Moffitt Field, California) and John E. Chambers, Department of Terrestrial Magnetism, Carnegie Institution of Washington (Washington D.C.), states that many objects, smaller than the Moon, probably were positioned at the L4 and L5 Lagrangian points of the Earth-Moon system. Lagrangian points (Lagrange points, or L-points) are five positions relative to two large celestial bodies in which small objects remain quasi- or firmly stationary with respect to the relative positions of these two larger bodies. At these five points, gravitational forces between the two large bodies are equal, and the position of a small object at each of these five points is always the same with respect to the two large bodies no matter where these two large bodies move in their orbits. For instance, Lagrangian points within the Earth-Moon system are areas in space where the gravitational force of the Moon on the Earth and the gravitational force of the Earth on the Moon are equal. Thus, any objects in these areas remain stationary (with respect to the movement of the two larger bodies) unless disturbed by an outside force such a wayward asteroid, comet, or meteoroid. For your information, here is a brief explanation of the location of these five Lagrangian points with respect to the larger bodies. The L1 point is a point on a straight line “between” two large bodies, which goes through both bodies’ center of mass. The L2 point is a point on the same straight line, but positioned on the “far” side of the “smaller” body with respect to the larger body. The L3 point is a point on the same straight line, but positioned on the “far” side of the “larger” body with respect to the smaller body. The orbits of objects on the L1, L2, and L3 points are called halo orbits. Some great “moving pictures” help to explain the relative positions of L1, L2, and L3. They appear on the European Space Agency website “What are Lagrange points?” The L4 and L5 points are points positioned behind of [L5] and in front of [L4] the two top corners of two equilateral triangles in the plane of orbit whose common base is the line between the centers of mass of the two bodies, which also includes the other four bottom corners of the two equilateral triangles. The L4 and L5 points for the Earth-Moon system lie 60 degrees ahead of and 60 degrees behind, respectively, of the Moon as it orbits the Earth. They are the only true stable points of the five Lagrangian points. L1, L2, and L3 are quasi-stable. For instance, when an artificial satellite is placed at the L1 point, periodic thrusts must be made to keep it at the L1 point. However, theoretically, an artificial satellite at the L4 or L5 points could remain stable for millions, even billions, of years without thrusting of its engines, as long as nothing disturbs its position. The orbits of objects at the L4 and L5 points are called Trojan orbits or triangular orbits. A mathematical explanation of the physics behind the L4 and L5 points is found at NASA’s website “The L4 and L5 Lagrangian Points. ” Now, back to why the Earth probably had more moons circling it in the past than just one. Please read on. |
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