All About Pluto and Dwarf Planets for Kids: Astronomy and Space for Children – FreeSchool

All About Pluto and Dwarf Planets for Kids: Astronomy and Space for Children – FreeSchool


You’re watching FreeSchool! Pluto, the ninth-largest body orbiting the
Sun, has been a matter of contention in recent years. Originally considered a planet following
its discovery in 1930, Pluto was regarded as the ninth planet in the solar system for
more than 75 years. In 2006, following the discovery of several other small planet-like
objects similar to Pluto, astronomers were forced to decide what makes a planet a planet,
instead of something else. According to the rules agreed upon by the International Astronomical
Union, Pluto was not really a planet, and on September 13, 2006, it was reclassified,
along with the other similar small bodies, as a ‘dwarf planet.’ Pluto is small – with a diameter of only two-thirds
that of Earth’s moon – and is made of rocky ice. Astronomers believe that it is about
two-thirds rock and one-third water ice. Even though Pluto is small, this much ice represents
more than three times the amount of water in all of Earth’s oceans combined. Pluto is
the largest dwarf planet in the solar system, but not the most massive: that title belongs
to Eris. Unlike the gas giants of the outer solar system, Pluto has no rings, but it does
have a thin atmosphere made mostly of nitrogen, with small amounts of methane and carbon monoxide. Pluto is 3.7 billion miles or 5.9 billion
kilometers away from the sun, with an orbit that takes 248 years to complete. Its orbit
is highly elliptical. Because of this, Pluto crosses inside of Neptune’s orbit for 20 years
of each 248-year orbit. Between 1979 and 1999, Pluto was actually closer to the Sun than
Neptune, something that won’t happen again for more than 200 years. Because Pluto is
so far from the Sun, it is a cold world. Temperatures there are about -390 F or -230 Celsius. Pluto
is also very dark: the amount of sunlight that reaches its surface is so little that
even on its brightest day, the sky would be in twilight. A day on Pluto lasts for about six and one-third
Earth days. Like Uranus, Pluto rotates on its side, something which results in extreme
seasonal changes with part of its surface in constant darkness and part of it in constant
daylight for decades. Pluto has five known moons, with the latest
moon discovered as recently as 2012. Its largest and closest moon, Charon, is so large compared
to Pluto that they actually orbit a point between each other, causing some astronomers
to call Pluto and Charon binary, or double, dwarf planets. Like Neptune, Pluto was initially discovered
through mathematical predictions rather than by observation. After Neptune was discovered
and studied, astronomers realized that there must be another planetary body out at the
edge of the solar system, and in 1906 Percival Lowell began an all-out search for a ninth
planet, called at the time ‘Planet X.’ Lowell died before the planet could be found, and
the search was interrupted for more than ten years. In 1929, young astronomer Clyde Tombaugh arrived
at Lowell’s observatory and was assigned to search through photographs of the night sky
to find anything that was shifting position. On February 18, 1930, after almost a year
of searching, Tombaugh found the elusive planet. The new planet was named Pluto after the Greek
god of the underworld, a name suggested by an eleven year old girl from England, Venetia
Burney. Beginning in 1992, many other objects were
found to be orbiting in the same area as Pluto. Currently more than 1,000 objects have been
discovered there, and scientists believe there may be as many as 100,000. This collection
of objects at the edge of the solar system is called the Kuiper Belt. It is similar to
the asteroid belt between Mars and Jupiter, but it is 20 times wider and perhaps as much
as 200 times more massive. As well, the Kuiper Belt is though to consist mainly of icy material,
whereas the asteroid belt is composed mostly of rock and metal. As more and more objects in the space surrounding
Pluto were discovered, astronomers began to question whether Pluto could truly be called
a planet. When Eris was discovered in 2005, it was briefly hailed as a tenth planet, but
it sparked a debate in the astronomical community about what makes a planet a planet. On August 24, 2006, the International Astronomical
Union declared that there are three conditions that must be met for an object in the Solar
System to be a planet. One, it must orbit around the Sun. Two, the object must be massive
enough for its own gravity to pull it into a spherical shape. And three, it must have
cleared the neighborhood around its orbit. Because of all the objects it shared its orbit
with, Pluto failed to meet the third condition, and along with Eris and other similar bodies,
was reclassified as a dwarf planet. There are currently five accepted dwarf planets
in the solar system, with hundreds more possible. Only one mission has traveled to Pluto, the
New Horizons space probe. It was launched on January 19, 2006, while Pluto was still
considered the ninth planet. The three billion mile journey took eight years, and it arrived
in Pluto’s system in July of 2015. New Horizons learned a great deal about Pluto’s atmosphere
and geography, as well as collecting information on Charon and Pluto’s smaller moons. The mission
uncovered many surprises about the dwarf planet, including strange formations that some are
calling ‘ice volcanoes’ on its surface. Dark, cold, and tiny, Pluto is still a source
of fascinating new discoveries for astronomers. I hope you enjoyed learning about Pluto, the
king of the Kuiper Belt. Goodbye till next time!

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