Why pluto demoted

It's only about half the width of the United States and lies in a far out region of the solar system called the Kuiper Belt, which requires a telescope to see. Read More. The dwarf planet was also famous for being the only planet to be discovered in the United States. The 1,pound piano sized probe, which was launched January 19, aboard an Atlas V rocket from Cape Canaveral, Florida, zipped by the planet yesterday.

It was spotted in by astronomer Clyde Tombaugh at Arizona's Lowell Observatory named after the otherwise respected American astronomer Percival Lowell who believed that Martians dug the canals found on that planet's surface. The story behind Pluto's name is also famous. It was suggested by an year-old girl in England, who was interested in Roman legends and thought naming the icy planet after the god of the underworld was intriguing.

Her grandfather relayed the idea to a member of the UK's Royal Astronomical Society, which then suggested it to their American counterparts at Lowell Observatory.

The newly discovered planet, orbiting more than 3 billion miles from the sun, would go on to be known as the "King of the Kuiper Belt. But how the mighty have fallen. And then there were eight. Things went downhill for Pluto in , when the IAU redefined what it means to be a planet, declaring that a planet must be a celestial body that orbits the sun, is round or nearly round, and "clears the neighborhood" around its orbit.

Pluto failed on the third account because its orbit overlaps with Neptune. The IAU reclassified it as a dwarf planet, also calling it a "Trans-Neptunian Object," which prompted outrage from schoolchildren, small planet enthusiasts, and the internet in general.

Photos: Pluto in glorious color images. Pluto's Brilliant 'Heart' — This high-resolution image captured by NASA's New Horizons spacecraft shows Pluto's surface has a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds.

The bright expanse is the western lobe of the "heart," informally known as Tombaugh Regio. The lobe, informally called Sputnik Planum, has been found to be rich in nitrogen, carbon monoxide, and methane ices.

Hide Caption. Pluto's Varied Terrain — Pluto taken by NASA's New Horizons spacecraft just before closest approach on July 14, , are the sharpest images to date of Pluto's varied terrain—revealing details down to scales of meters.

In this mile kilometer section, the textured surface of the plain surrounds two isolated ice mountains. The mosaic shows how Pluto's large-scale color patterns extend beyond the hemisphere facing New Horizons at closest approach, which were imaged at the highest resolution. But over subsequent decades, astronomers began to wonder whether Pluto might simply be the first of a population of small, icy bodies beyond the orbit of Neptune.

This region would become known as the Kuiper Belt, but it took until for the first "resident" to be discovered. Confirmation of the first KBO invigorated the existing debate. And in , the Hayden Planetarium in New York became a focus for controversy when it unveiled an exhibit featuring only eight planets. The planetarium's director Neil deGrasse Tyson would later become a vocal figure in public discussions of Pluto's status.

But it was discoveries of Kuiper Belt Objects with masses roughly comparable to Pluto, such as Quaoar announced in , Sedna and Eris , that pushed the issue to a tipping point. Eris, in particular, appeared to be larger than Pluto - giving rise to its informal designation as the Solar System's "tenth planet". Prof Mike Brown of the California Institute of Technology Caltech , who led the team that found Eris, would later style himself as the "man who killed Pluto" , while deGrasse Tyson would later jokingly quip that he had "driven the getaway car".

The finds spurred the International Astronomical Union to set up a committee tasked with defining just what constituted a planet, with the aim of putting a final draft proposal before members at the IAU's General Assembly in Prague. Under a radical early plan, the number of planets would have increased from nine to 12 , seeing Pluto and its moon Charon recognised as a twin planet, and Ceres and Eris granted entry to the exclusive club. But the idea met with opposition. The discussions in Prague during August were intense, but a new version of a planetary definition gradually took shape.

On 24 August, the last day of the assembly, members voted to adopt a new resolution outlining criteria for naming a planet:. Pluto met the first two of the these criteria, but the last one proved pivotal. In other words, it has achieved gravitational dominance. Pluto was discovered in by astronomer Clyde W. Tombaugh at the Lowell Observatory in Flagstaff, Arizona. The dwarf planet's name was given by an year-old girl, Venetia Burney, who lived in Oxford, England at the time. On hearing about the planet's discovery, she told her grandfather the distant world should be named after Pluto, the Roman god of the underworld.

Pluto really is tiny. At around 1, miles wide, Pluto isn't even as big as the Earth's moon and is only half as wide as the U. Pluto's biggest moon, Charon, is roughly half as big as Pluto itself. It's also distant.