Pluto's surface is one of the coldest places in the solar system. NASA's Hubble Space Telescope has also revealed evidence that Pluto's crust could contain complex organic molecules. It's possible the lines are created by harsh winds blowing across the dwarf planet's surface. These icy plains also display dark streaks that are a few miles long and aligned in the same direction. It's possible that this region is still being shaped and changed by geologic processes. This region of Pluto's surface lacks craters caused by meteorite impacts, suggesting that the area is, on a geologic timescale, very young - no more than 100 million years old. In the center-left of Tombaugh Regio is a very smooth region unofficially known by the New Horizons team as "Sputnik Planum," after Earth's first artificial satellite, Sputnik. Other variations in the composition of surface materials have been identified within the "heart" of Pluto. The left side of the region (an area that takes on the shape of an ice cream cone) is covered in carbon monoxide ice. The Pluto features are much larger they are estimated at 1,650 feet (500 m) tall, while the Earth features are only a few meters in size.Īnother distinct feature on Pluto's surface is a large heart-shaped region known unofficially as Tombaugh Regio (after Clyde Tombaugh regio is Latin for region). The dwarf planet also possesses ice ridge terrain that appears to look like a snakeskin astronomers spotted similar features to Earth's penitentes, or erosion-formed features on mountainous terrain. Pluto's surface is also covered in an abundance of methane ice, but New Horizons scientists have observed significant differences in the way the ice reflects light across the dwarf planet's surface. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute) The surface of Pluto as seen from NASA's New Horizons during its July 2015 flyby. While methane and nitrogen ice cover much of the surface of Pluto, these materials are not strong enough to support such enormous peaks, so scientists suspect that the mountains are formed on a bedrock of water ice. Observations of Pluto's surface by the New Horizons spacecraft revealed a variety of surface features, including mountains that reach as high as 11,000 feet (3,500 meters), comparable to the Rocky Mountains on Earth. New Horizons showed that Pluto has a diameter of 1,473 miles (2,370 km), less than one-fifth the diameter of Earth, and only about two-thirds as wide as Earth's moon. Since Pluto is so far from Earth, little was known about the dwarf planet's size or surface conditions until 2015, when NASA's New Horizons space probe made a close flyby of Pluto. This "snow" falls to Pluto's surface a reddish gray. As the haze particles get more massive, they start to fall through the atmosphere, collecting more ice. As the ions interact with each other, they combine into more complex molecules, and start to collect an outer shell of volatile ices. These particles start out high in Pluto's atmosphere as ionized methane and nitrogen. There are also haze particles in Pluto's atmosphere, which scatter blue light. Much like its crust, Pluto's atmosphere is composed of nitrogen, methane, and carbon monoxide. The surface crust is a layer of various ices, mostly nitrogen ice, with giant mountains of water ice, and traces of methane and carbon monoxide ices. Outside of that, but still deep in the interior, there's likely an ocean of water, covered by another layer of frozen water ice. So, rather than being the runt of the planet group, Pluto is now the "king" of the dwarf planet group!Īstronomers believe that Pluto probably has a rocky core. Even one of its own moons, Charon, is about half of Pluto's size. Pluto satisfies the first two of these criteria, but not the third. The three rules astronomers of the International Astronomical Union came up with to define a planet are: The object must orbit the sun the object must be massive enough to be roughly spherical and the object must have cleared its orbit of any objects of comparable mass to its own (that is, it must be gravitationally dominant in its orbit). Finding all these new objects, it became necessary for astronomers to get more specific about what we mean by the word "planet," and figure out which category Pluto fit into. More like Pluto, in some ways, than Pluto is like the other planets. But as astronomers discovered more and more about the Kuiper Belt (and the asteroid belt between Mars and Jupiter), we learned that there are lots of objects like Pluto. Why is Pluto no longer considered a planet?įor a long time, we thought Pluto was unique in the Kuiper Belt. Emily Safron is an astronomy instructor at Case Western Reserve University.
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