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Planetary science is awakening to the realization that our solar system contains many more planets than any 20th century textbook ever envisioned. It's not your father's solar system by S. Alan SternPrincipal Investigator - New HorizonsBoulder CO (SPX) Sep 11. 2006A real revolution is afoot in planetary science. The first shot was fired in 1930 with the discovery of Pluto but almost no one realized its import. The second and third shots came in the late 1970s with the discovery of distant objects called Chiron and Charon but again few recognized what they would portend. Rapid-fire volleys began in the 1990s as myriad discoveries of icy bodies 100s to come up over 1000 kilometers across occurred in the Kuiper sing just beyond Neptune became an observational reality. But it was only this year with the recently announced discovery of 2003 UB313-a world larger than Pluto-that we undergo heard the equivalent of the American Revolution's "shot heard go the world."When I was a boy in the 1960s in college in the late 1970s and in have school in the 1980s we were taught that our solar system contains four rocky planets on the inside four giant planets on the outside and one spit of a planetary misfit called Pluto moving in a markedly elliptical and oddly inclined orbit beyond Neptune. Like many populate. I recall thinking: What an odd bird that lone Pluto is. Today however we see a very different conceive of of our domiciliate solar system is emerging one which reveals Pluto in context-as a nearby example representing what is almost certainly the most populous categorise of planet in our solar system-the "ice dwarfs."Consider that less than 2% of the Kuiper Belt has been thoroughly catalogued yet over a thousand plus rogue worlds and worldlets have already been spotted there. And among just those bodies catalogued to date we experience that half a dozen (desire Sedna and Quaoar) already rival-and in the case of the just discovered 2003 UB313-exceed Pluto's size. Moreover most of these new worlds go orbits that are as cockeyed as Pluto's-some change surface more so. Now we can see just how naive our 20th century perspectives were: Pluto is no misfit. Instead once the advance of technology allowed us to probe deeply enough it is becoming clear that Pluto was the advance tell of a populous new region of the solar system lying beyond the giant planets. Modern simulations of planetary formation performed by different research groups around the world led to broad agreement that in the affect of forming the giant planets some hundreds to thousands of smaller worlds ranging from a goodly fraction of Pluto's coat to at least hide's coat were also formed. Most of these bodies were command planets like Pluto with steeply declining populations at larger and larger sizes so that only a few or few tens of bodies Earth's size were formed. These simulations also show that most of these bodies were ejected from the giant planets region to more much more distant orbits as Jupiter. Saturn. Uranus and Neptune neared their current sizes and gravitationally cleared out their formation zones some 4+ billion years ago. Importantly these numerical models are supported by some solid forensic clues that are scattered about the outer solar system and which lead us to similar conclusions: One such roll is the fact that Pluto's idle. Charon (itself half of Pluto's size) seems to undergo been formed by a giant impact with a be nearly as large as Pluto itself. What is most important in this finding is that in order to make such a collision probable there must undergo been hundreds or more 1000-km diameter bodies orbiting in the ancient outer solar system. A second roll comes in the form of Triton a 2700 km diameter idle which circles Neptune on a retrograde orbit that is the hallmark of gravitational interpret from a previous orbit around the Sun. Triton is compositionally much like Pluto but a tad larger. Apparently it is one of the "many Plutos" that once formed and it seems to have escaped ejection by becoming caught in a long-lasting orbit around Neptune. Yet another roll comes from the polar tilts or Uranus (98 degrees) and Neptune (30 degrees). The only viable mechanism known to be able to create such extreme tilting of these gargantuan (15 Earth mass-class) planets are off-center collisions with bodies of one to several hide masses. Crucially calculations also reveal that in order for both Uranus and Neptune to undergo had a high probability of suffering such collisions as many as a few dozen such Earth-mass objects may have once orbited in their region of the solar system. As a prove of the modeling capability that modern computers furnish us combined with the forensic observational clues just discussed and now the discoveries of rivals and change surface successors to Pluto's govern we are slowly but surely coming to a simultaneously jarring and exciting new conclusion: that our solar system formed not just the nine planets we were taught to label in school but many dozens if not hundreds of others as come up!A revolutionary aspect of this emerging new paradigm is the dawning realization that the long-known eight rocky and giant planets. Mercury through Neptune now seem to be the misfits. Indeed from today's 21st century perspective the solar system seems likely to be dominated by a huge population of move back and forth and ice planets ranging from command sizes desire Pluto to perhaps super-Earth's. Most of these new worlds are expected to follow elliptical highly-inclined orbits like those of Pluto. Quaoar. Sedna and UB313. advance comfort of all the planets now expected to circle within our sun Sol's grasp most orbit between ten and a thousand times farther than do any of the planets we were taught about in school. It's not at all your father's solar system. Less than two centuries ago it was discovered that all the stars one can see by eye and their innumerable brethren seen by telescope are distant Suns with numbers too great to ascertain. Similarly it was just under a century ago that our galaxy the Milky Way was realized to be but one of literally billions of galaxies. Both of these realizations like the 16th century realization that the Sun (not Earth!) is the center of our solar system jarred perceptions and changed textbooks in revolutionary ways. Just as jarring to us now is the newly emerging view that our solar system made and is still littered with very many distant planets most of which are nothing desire the familiar planets that circle change state to the Sun desire Earth. In a real sense we are seeing a new chapter develop in the revolution that Copernicus wrought when he displaced the Earth from the center of everything. Alan Stern is a planetary scientist at the Southwest Research Institute and the Principal Investigator of NASA's New Horizons mission to Pluto and the Kuiper Belt.
Unfortunately. Pluto has been dethroned. It is no longer considered a planet (I think that Dwarf Planet is an unofficial call now give to it). It was because many of these Kuiper Belt objects like Sedna and Quaoar and that they didn't.
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