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The smallest and most-distant planet in our solar system is tiny, icy Pluto. It is even smaller than our moon, and it wasn't discovered until 1930 — the only planet discovered in the twentieth century. Pluto is about one-fifth the diameter of Earth, and it is named after the Roman god of the underworld, who could make himself invisible. Pluto and Charon Unlike the other outer planets, Pluto is terrestrial. Its atmosphere is mostly nitrogen, and, unexpectedly, it seems to be expanding. Whatever heat reaches Pluto is not enough to warm the surface of the planet. The planet's atmospheric temperature varies between around -235° and -170° Celsius, depending on the altitude above the surface. Pluto is so far from the sun, it takes 247.7 Earth years to orbit the sun. Its icy moon, Charon, is so large (relatively) and close, it revolves around Pluto in about six days and nine hours, meaning that it has the second slowest rotation speed in the solar system (after Venus, which takes 243 days to turn on its axis). Pluto and Charon were probably Kuiper Belt objects (the Kuiper Belt is an area beyond Neptune's orbit). Pluto is a very dark, cold place, and it's been getting even darker since 1954. The sun that provides Earth with light and heat is just another light in the sky to Pluto because it is so far away. Although Pluto is said to be the most-distant planet in the solar system, its orbit is so elliptical that for about 20 years of its 248-year orbit, the tiny planet is a little closer to the sun than Neptune. For most of the time, though, Pluto really is the most-distant planet in the solar system. How Pluto Differs from Other Planets Even the Hubble Space Telescope can only get a very faint picture of Pluto and Charon. Charon is more than half as large as Pluto itself, making it closer in size to its parent planet than any other moon in the solar system. You could almost think of Pluto and Charon as a very tiny double planet system. They are the only bodies in our solar system where both are locked in rotation. That means Charon keeps its same face toward Pluto, and Pluto keeps its same face toward Charon. There are some who argue that Pluto's not a planet at all, but an escaped moon of Jupiter, or that it is actually an asteroid that drifted into a remote orbit around the sun. Pluto is the only planet in our solar system that has not yet been visited by a spacecraft. This may change though when NASA's New Horizon spacecraft arrives there, which may be as early as summer 2015.
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Znanstvenici javljaju da su NASA/ESA-inim svemirskim teleskopom Hubbleom otkrili peti mjesec koji kruži oko patuljastog ledenog planeta Plutona Novi mjesec, vidljiv u obliku mrlje svjetlosti na Hubbleovim fotografijama (pogledajte dolje), nepravilna je oblika i promjera između 10 i 25 kilometara. Oko Plutona se kreće na orbiti promjera 95.000 km koja leži u istoj ravni u kojoj kruže i ostali poznati mjeseci patuljastog planeta. 'Ovi mjeseci oblikuju niz pravilno poredanih orbita nalik na ruske babuške', rekao je voditelj istraživanja Mark Showalter iz Instituta SETI u Mountain Viewu. Znanstvenici osobito zanimljivom smatraju činjenicu da tako mali planet ima toliko složenu zbirku satelita. Mjesec, zasad poznat samo kao P5, trebao bi pomoći u otkrivanju načina na koji se ova kolekcija formirala. Prema najvjerojatnijoj teoriji, mjeseci su ostaci sudara Plutona i drugog velikog ledenog tijela iz Kuiperova pojasa prije nekoliko milijardi godina. Plutonov najveći mjesec, Haron, otkriven je 1978. godine. Prije šest godina uz pomoć Hubblea otkrivena su još dva manja mjeseca, Nikta i Hidra, a prošle godine i mjesec koji još uvijek nosi radni naziv P4. Pluton je 1930. godine otkrio Amerikanac Clyde Tombaugh, a sve do nove kategorizacije u patuljasti planet 2006. smatrao se devetim planetom Sunčeva sustava. NASA-in satelit New Horizons trenutno putuje prema Plutonu. Pokraj njega će proletjeti 2015. godine. Na Zemlju bi trebao poslati prve detaljne snimke Plutonova sustava koji je toliko malen i dalek da čak i teleskop Hubble jedva vidi najveće strukture na njegovoj površini. Nakon ovog proleta astronomi planiraju nastaviti istraživanja Plutonova sustava Hubbleovim nasljednikom infracrvenim svemirskom teleskopom James Webb koji bi trebao istražiti kemijska svojstva njegovih, ali i brojnih drugih tijela u Kuiperovu pojasu. - Sviđa vam se članak? Preporučite ga prijateljima putem ovih servisa: Pošaljite mailom