Some astronomers thought Eris could be bigger than Pluto, but Nasa appear to have settled that argument today as the space agency’s New Horizons spacecraft approaches Pluto after a decade-long journey.Īlan Stern, the mission’s principle investigator, said: “We have discovered that Pluto is a little bit larger then we anticipated. There are five others: Ceres, the possibly rugby ball-shaped Haumea, Makemake and Eris. No longer a full planet, Pluto is classed as a “dwarf planet”. Geology of Pluto, captured by New Horizons (Picture: Nasa) The five dwarfs It is not the first time the list of planets has shrunk: between 18 Ceres was counted as a planet in many textbooks, before being reclassified as an asteroid. Some astronomers think the “clearing the neighbourhood” definition is too vague, or impossible to achieve for celestial bodies in the crowded Kuiper Belt. The decision remains controversial, as only a few hundred of the union’s 10,000 or so members voted for the momentous change. It had not swept away other smaller objects in its orbital region. have “cleared the neighbourhood” around its orbitĪstronomers decided that Pluto did not meet the last of the three criteria.be massive enough for its own gravity to pull it into a roughly round shape.In order to be worthy of the name, an object must: Should Eris become the 10th planet in the solar system, or should Pluto be stripped of its status? What was a planet anyway?Īfter lengthy debate, the IAU proposed a new definition of “planet”. In 2006 the International Astronomical Union (IAU) held a meeting to decide what to do about Eris and Pluto. Then, in 2005, a team led by American astronomer Mike Brown discovered Eris, another distant object orbiting the sun that appeared to be more massive than Pluto. It became increasingly clear that Pluto was just one of thousands of bodies in the belt. More powerful telescopes had begun to pick up other objects forming the Kuiper Belt – a region of space beyond the orbit of Neptune. Pluto’s status as a planet was called into question as early as 1992. Generations of children remembered the order of nine planets orbiting the sun with mnemonics like My Very Excellent Mother Just Served Up Nine Pizzas. Pluto was discovered by American astronomer Clyde Tombaugh in 1930, after a long search for an unseen “planet X” beyond Neptune that was thought to be disrupting the orbits of the giant planets. There were nine planets circling the sun, from boiling Mercury to distant, mysterious Pluto. Have fun, and keep exploring.For anyone who went to school before 2006, the solar system was a simpler place. It may not work properly on older mobile devices. Use the HD button to upload higher-resolution imagery of the planets. Active international missions such as Japan's Akatsuki Venus Orbiter and ESA and Japan's Mercury-bound BepiColombo are not yet available. Showcasing the entire operating international fleet is too much of a data wallop at the moment (but we are working on it!). This snapshot focuses on active NASA missions and select ESA missions. This digital orrery (a model of the solar system) runs on a light, mobile-mobile friendly version of NASA's Eyes on the Solar System software. The position of the planets, moons, and spacecraft are shown where they are right now. This simulated view of our solar system at the top of this page (and below) runs on real data. Real-Time, Real Data: Your Galactic Neighborhood They’re considered dwarfs because they are massive, round, and orbit the Sun, but haven't cleared their orbital path. Except for Ceres, which lies in the main asteroid belt, these small worlds are located in the Kuiper Belt. The five best-known dwarf planets are Ceres, Pluto, Makemake, Haumea, and Eris. There are likely thousands of dwarf planets waiting to be discovered beyond Neptune. Like planets, dwarf planets are generally round (Haumea looks like an overinflated football) and orbit the Sun. Pluto, for example, has not cleared its orbit of similar objects while Earth or Jupiter have no similarly-sized worlds on the same path around the Sun. The key difference between a planet and a dwarf planet is the kinds of objects that share its orbit around the Sun.
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