Pluto - the dwarf planet

Northern hemisphere of Pluto in true color, taken by NASA's New Horizons probe in 2015. Credit: https://en.wikipedia.org/

 Pluto is a dwarf planet located in the Kuiper Belt, a region of the solar system beyond Neptune that is populated by small, icy objects. It was discovered in 1930 by Clyde Tombaugh, an American astronomer, and was originally classified as the ninth planet in the solar system. However, in 2006, the International Astronomical Union (IAU) reclassified Pluto as a "dwarf planet," a new category of celestial body that is smaller than a planet but larger than an asteroid or a comet.

Pluto is about two-thirds the size of Earth's moon and is made up mostly of rock and ice. It has a surface covered in frozen methane, ammonia, and water, and it has a thin atmosphere that expands and contracts as the planet moves closer to and farther from the sun. Pluto has five known moons, the largest of which is named Charon.

Pluto's orbit around the sun is highly elliptical, meaning that it is much farther from the sun at some points in its orbit than at others. As a result, Pluto experiences extreme temperature variations, ranging from about -235 degrees Celsius (-391 degrees Fahrenheit) at its coldest to about -15 degrees Celsius (5 degrees Fahrenheit) at its warmest.

Despite its reclassification as a dwarf planet, Pluto remains an important object of study for astronomers and space scientists, who are interested in learning more about the early history and evolution of the solar system. In 2015, NASA's New Horizons spacecraft conducted a flyby of Pluto, gathering data and returning the first detailed images of the planet.

Pluto's reclassification as a dwarf planet sparked a debate among scientists and the general public about what should be considered a "planet." The IAU defines a planet as a celestial body that orbits the sun, is round due to its own gravity, and has "cleared its orbit" of other objects. According to this definition, Pluto does not qualify as a planet because its orbit overlaps with the orbit of Neptune and it shares its orbit with other objects in the Kuiper Belt.

Despite its reclassification, Pluto is still considered an important object in the solar system and is of great interest to scientists. It is thought to be a remnant from the early solar system and may provide clues about the conditions that existed in the solar system when it formed 4.6 billion years ago.

Pluto is also the first object in the Kuiper Belt to be visited by a spacecraft. In 2015, NASA's New Horizons spacecraft conducted a flyby of Pluto, gathering data and returning the first detailed images of the planet and its moons. The mission was a major scientific success, revealing a wide range of geological features on Pluto's surface, including mountains, plains, and valleys, as well as a vast, glacier-like region known as Sputnik Planum.

In addition to its scientific importance, Pluto has also captured the public's imagination and has become a popular cultural icon. It has inspired many works of science fiction, including the Pixar film "WALL-E," in which a character named EVE travels to Pluto in search of life.

Pluto has five known moons, the largest of which is named Charon. Charon is about half the size of Pluto and is thought to be made up of rock and water ice. It was discovered in 1978 by James W. Christy, an American astronomer. The other four moons of Pluto are much smaller and were discovered more recently. They are named Styx, Nix, Kerberos, and Hydra.

Pluto's orbit around the sun is highly elliptical, meaning that it is much farther from the sun at some points in its orbit than at others. This means that Pluto experiences extreme temperature variations and takes 248.09 Earth years to complete one orbit around the sun.