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The New Solar System  A controversial new proposal by the International Astronomical Union would reclassify an asteroid and a moon as planets, plus add one far-out object. Here's the whole mix. Continue to see each of the 12 "planets."  The new planet definition relies on gravity as a determining factor. With a certain amount of mass, gravity makes planets like Mercury round. To be a planet, an object also has to orbit a star and not orbit another planet. Mercury is a terrestrial, or rocky planet. Mercury is 3,031 miles wide, the smallest of the inner rocky planets.  This terrestrial planet is 7,521 miles wide and known for having a scorching surface brought on by a runaway greenhouse effect. Thick clouds obscure the entire surface ofVenus.  Earth is 7,926 miles in diameter, the largest of the known terrestrial planets. Some astronomers speculate that at least one object as big as Earth might yet be found in theouter solar system.  Mars is the only planet in our solar system besides Earth that has much chance of harboring life. It is 4,217 miles wide.  The first asteroid, Ceres, was discovered in 1801. At 580 miles wide, it's about one-fifth the diameter of Mercury. The new definition would return it to planet status. The IAU suggests calling it a dwarf planet. A few other asteroids might be reclassified after further research.  The biggest planet in the solar system, Jupiter has long been termed a gas giant. At 88,730 miles in diameter, it is 11.2 times wider than Earth and 317.8 times as massive. Some planets around other stars are much more massive.  The ringed planet is 74,900 miles wide. That's 9.4 times the diameter of Earth. It is 95 times as massive as our plane.  Typically called a gas giant, Uranus is really mostly ice. It’s 31,763 miles wide, which is only 4.1 times the diameter of Earth.  At 30,775 miles wide, icy Neptune is just 3.9 times the diameter of Earth. Technology lately has allowed astronomers to find planets this small around other stars, too.               The New Solar SystemThe planet that started all this controversy would now be considered the first Plutino, a new class of relatively small planets out beyond Neptune that carve odd orbits. Pluto, is 1,430 miles wide, or about 18 percent Earth’s diameter, and just 0.2% of Earth’s mass.  Long termed a moon of Pluto, Charon is the largest moon in the solar system relative to the object it orbits with. The orbital center of this two-object system is actually in the space between them, so the new definition would term this a double-planet system.  This object, popularly called Xena, will eventually get some other formal name. Under the new definition, it would become the most distant planet in our solar system. The object is about 1,490 miles wide with an uncertainty of 60 miles, meaning its roughly the same size as Pluto. |
