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Posted on 04/15/2009 8:45:07 AM PDT by TaraP
STEREO Hunts for Remains of an Ancient Planet near Earth
April 9, 2009: NASA's twin STEREO probes are entering a mysterious region of space to look for remains of an ancient planet which once orbited the Sun not far from Earth. If they find anything, it could solve a major puzzle--the origin of the Moon.
The name of the planet is Theia," says Mike Kaiser, STEREO project scientist at the Goddard Space Flight Center. "It's a hypothetical world. We've never actually seen it, but some researchers believe it existed 4.5 billion years ago—and that it collided with Earth to form the Moon."
The "Theia hypothesis" is a brainchild of Princeton theorists Edward Belbruno and Richard Gott. It starts with the popular Great Impact theory of the Moon's origin. Many astronomers hold that in the formative years of the solar system, a Mars-sized protoplanet crashed into Earth. Debris from the collision, a mixture of material from both bodies, spun out into Earth orbit and coalesced into the Moon. This scenario explains many aspects of lunar geology including the size of the Moon's core and the density and isotopic composition of moon rocks
It's a good theory, but it leaves one awkward question unanswered: Where did the enormous protoplanet come from?
Belbruno and Gott believe it came from a Sun-Earth Lagrange point.
Sun-Earth Lagrange points are regions of space where the pull of the Sun and Earth combine to form a "gravitational well." The flotsam of space tends to gather there much as water gathers at the bottom of a well on Earth. 18th-century mathematician Josef Lagrange proved that there are five such wells in the Sun-Earth system: L1, L2, L3, L4 and L5 located as shown in the diagram below.
When the solar system was young, Lagrange points were populated mainly by planetesimals, the asteroid-sized building blocks of planets. Belbruno and Gott suggest that in one of the Lagrange points, L4 or L5, the planetesimals assembled themselves into Theia, nicknamed after the mythological Greek Titan who gave birth to the Moon goddess Selene.
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Just adding to the catalog, not sending a general distribution. |
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