Amazing Astronomy

                                                                             D. L. Rabinowitz


                                                             Eris was first spotted in 2003 during a Palomar Observatory survey of the outer solar system by Mike Brown, a professor of planetary astronomy at the California Institute of Technology; Chad Trujillo of the Gemini Observatory; and David Rabinowitz of Yale University. The discovery was confirmed in January 2005, and was submitted as a possible 10th planet of our solar system since it was the first object in the Kuiper Belt found to be bigger than Pluto.Eris is named for the ancient Greek goddess of discord and strife. The name fits since Eris remains at the center of a scientific debate about the definition of a planet.Eris' moon, Dysnomia, is named after Eris' daughter who is the demon goddess of lawlessness.





                                                            It takes icy Eris 557 Earth years to complete a single orbit around our sun. The plane of Eris' orbit is well out of the plane of the solar system's planets and extends far beyond the Kuiper Belt, a zone of icy debris beyond the orbit of Neptune.The dwarf planet is often so far from the sun that its atmosphere collapses and freezes on the surface in an icy glaze. The coating gleams brightly, reflecting as much sunlight as freshly fallen snow. Scientist's believe surface temperatures to vary from about -359 degrees Fahrenheit (-217 degrees Celsius) to -405 degrees Fahrenheit (-243 degrees Celsius). The thin atmosphere will thaw in hundreds of years as Eris gets closer to the sun, revealing a rocky surface scientists believe is similar to Pluto.





                                                          Though the dwarf planet Eris on the edge of the solar system is much denser than Pluto, the two frigid worlds are nearly exactly the same size, a new study finds.Astronomers accurately measured Eris' diameter for the first time using observations made late last year, when they caught the dwarf planet as it passed in front of a dim star. The observations, made using several telescopes in Chile, revealed that Eris and Pluto are pretty much identical in size, making them "almost perfect" twins, researchers said.The researchers also conclude that Eris is a spherical body. And, by studying the motion of Eris' moon Dysnomia, they peg the dwarf planet to be about 27 percent heavier than Pluto, which means it's considerably denser than Pluto as well.

                                                Ceres is the only dwarf planet not found in the freezing cold, faraway Kuiper Belt. Rather, it orbits in the main asteroid belt between Mars and Jupiter, completing one lap around the sun every 4.6 years and its rotation period is 9.075 hours.Ceres is by far the largest object in the asteroid belt, containing about one-third of the belt's mass. However, at 590 miles (950 km) across, it is the smallest known dwarf planet. It is named after the Roman goddess of the harvest and motherly love.Because it's so much closer to Earth than the other dwarf planets, Ceres was discovered far earlier. Italian astronomer Giuseppe Piazzi spotted it first, on Jan. 1, 1801. For the next half-century, many astronomers regarded Ceres as a true planet.
                                                     Because Ceres is spherical, it is unlike the majority of the members of the asteroid belt. Its composition is also slightly different than its neighbors in the belt. Its surface is probably covered with a mixture of water ice, carbonates, and clays. This leads astronomers to believe that it formed differently from the other bodies in the asteroid belt. It is now believed that Ceres formed 4.6 billion years ago when the solar system was forming. Apparently, Ceres never accumulated enough matter to get larger than the 950 kilometers in diameter that it currently is. Ceres contains one-third of the mass found in the asteroid belt.Scientists believe that Ceres has a rocky core and an icy mantle. Some scientists also believe that it has a liquid water layer in its interior. This possibility makes Ceres very intriguing to scientists that are searching for signs of extraterrestrial life

                                                  Ceres has a very primitive surface and like a young planet, contains water-bearing minerals, and possibly a very weak atmosphere and frost. Infrared observations show that the surface is warm with a possible maximum temperature of 235 K (-38°C). Ceres ranges in its visual brightness magnitude from +6.9 to +9.. At its brightest point it is just barely too dim to be seen with the naked eye.

                                                     Ceres follows an orbit between Mars and Jupiter, within the asteroid belt, with a period of 4.6 Earth years The orbit is moderately inclined (i = 10.6° compared to 7° for Mercury and 17° for Pluto) and moderately eccentric (e = 0.08 compared to 0.09 for Mars).

                                                      Scientists and the world will get a much better look at Ceres less than four years from now. In February 2015, NASA's Dawn spacecraft — which is currently orbiting Vesta, the asteroid belt's second-largest resident — will arrive at Ceres to undertake a detailed study of the dwarf planet.

                                                Since Pluto is so far from Earth, little is known about the planet’s size or surface conditions. Pluto has an estimated diameter less than one-fifth that of Earth or only about two-thirds as wide as Earth's moon. The planets’ surface conditions probably consist of a rocky core surrounded by a mantle of water ice, with more exotic ices such as methane and nitrogen frost coating its surface.
                                                  Pluto's orbit is highly eccentric, or far from circular, which means its distance from the sun can vary considerably and at times, Pluto’s orbit will take within the orbit of the planet Neptune. When Pluto is closer to the sun, its surface ices thaw and temporarily form a thin atmosphere, mostly of nitrogen, with some methane. Pluto's low gravity, which is a little more than one-twentieth that of Earth's, causes this atmosphere to extend much higher in altitude than Earth's. When traveling farther away from the Sun, most of Pluto's atmosphere is thought to freeze and all but disappear. Still, in the time that it does have an atmosphere, Pluto can apparently experience strong winds.Pluto's surface is one of the coldest places in the solar system at roughly minus 375 degrees F (minus 225 degrees C). For a long time, astronomers knew little about its surface because of its distance from Earth, but more is coming, bit by bit, with the Hubble Space Telescope returning images of a planet that appears reddish, yellowish and grayish in places, with a curious bright spot near the equator that might be rich in carbon monoxide frost. When compared with past images, the Hubble pictures revealed that Pluto had apparently grown redder over time, apparently due to seasonal changes.


 Pluto's Moons : 
                The innermost moon, Charon, was discovered by James Christy on June 22, 1978.
                                            Pluto and Charon are just 12,200 miles (19,640 kilometers) apart, less than the distance by flight between London and Sydney. Charon's orbit around Pluto takes 6.4 Earth days, and one Pluto rotation — a Pluto day — also takes 6.4 Earth days. This is because Charon hovers over the same spot on Pluto's surface, and the same side of Charon always faces Pluto, a phenomenon known as tidal locking.While Pluto appears reddish, Charon seems grayish. Scientists suggest Pluto is covered with nitrogen and methane while Charon is covered with ordinary water ice.Compared with most of solar system's planets and moons, the Pluto-Charon system is tipped on its side in relation to the sun. Also, Pluto's rotation is retrograde compared to the other worlds — it spins backwards, from east to west
                                             In 2005, as scientists photographed Pluto with the Hubble Space Telescope in preparation for the New Horizons mission — the first spacecraft to visit Pluto and the Kuiper Belt — they discovered two other tiny moons of Pluto, now dubbed Nix and Hydra. These are two to three times farther away from Pluto than Charon, and they are thought to be just 31 to 62 miles (50 to 100 kilometers) wide.
Scientists using Hubble discovered a fourth moon in 2011. This moon is estimated to be 8 to 21 miles (13 to 34 km) in diameter. P4's orbit is between the orbits of Nix and Hydra. On July 11, 2012, a fifth moon was discovered P5.

Exploration: 

 

                         NASA's New Horizons mission will be the first probe to study Pluto, its moons, and other worlds within the Kuiper Belt. It was launched on January 2006, making its closest approach to Pluto on July 2015, and carries some of the ashes of Pluto's discoverer, Clyde Tombaugh.

 

 Why Pluto is No Longer a Planet

 

                             For an object to be a planet, it needs to meet these three requirements defined by the IAU:

• It needs to be in orbit around the Sun – Yes, so maybe Pluto is a planet.
• It needs to have enough gravity to pull itself into a spherical shape – Pluto…check
• It needs to have “cleared the neighborhood” of its orbit – Uh oh. Here’s the rule breaker. According to this, Pluto is not a planet.

                               .                              According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.
                              Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.
                              In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.
                                Any object that doesn’t meet this 3rd criteria is considered a dwarf planet. And so, Pluto is a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.

                                                      Dwarf planets are worlds that are too small to be considered full-fledged planets, but too large to fall into smaller categories.In recent years, there's been a lot of hubbub about Pluto losing its status as one of the planets in our solar system. Pluto is no longer considered the ninth planet in the series of major planetary objects, but instead is now just one of the many so-called "dwarf planets." Astronomers estimate that there could be as many as 200 dwarf planets in the solar system and Kuiper Belt.
                                                       The International Astronomical Union defines a planet as being in orbit around the sun, has enough gravity to pull its mass into a rounded shape (hydrostatic equilibrium), and has cleared its orbit of other, smaller objects. This last criterion is the point at which planets and dwarf planets differ. A planet's gravity either attracts or pushes away the smaller bodies that would otherwise intersect its orbit; the gravity of a dwarf planet is not sufficient to make this happen
 
                                                        Pluto, Eris, Haumea, and Makemake are all known as "plutoids," unlike the asteroidal dwarf planetoid Ceres. A plutoid is a dwarf planet with an orbit outside that of Neptune. Plutoids are sometimes also referred to as "ice dwarfs" due to their diminutive size and cold surface temperatures.
                                                         The outer planets show evidence of interaction with plutoids. The largest moon of Neptune is likely a captured plutoid, and it is even possible that the odd tilt of Uranus on its axis is due to a collision with a plutoid. Similarly to dwarf planets, there are potentially hundreds of plutoid objects in the solar system that have yet to be given official status.


Facts : 
              In 2006 the International Astronomical Union adopted the term ‘dwarf planet’ for solar system objects that were bigger than small solar system bodies such as comets and asteroids but not quite planets.

               All the dwarf planets are found in the Kuiper Belt with the exception of Ceres which is found in the asteroid belt.

               No dwarf planets have yet been visited by space probes though in 2015 NASA’s Dawn and New Horizons missions will reach Ceres and Pluto respectively.