Overview: Discovery of a New Planet
The dwarf planet Pluto has always been a mystery. In the 19th century, the planets Uranus and Neptune were discovered. However, there were questions about the orbit of Neptune that led astronomers to suspect the existence of an unknown planet they called Planet X. A very young astronomer named Clyde Tombaugh just started working at Lowell Observatory, and he was assigned to survey pictures taken from the telescope to see if any objects were moving strangely. By coincidence, he discovered a possible planet in 1930, which was later called Pluto. It was named Pluto for the Roman god of the underworld, and also for the founder of the observatory, Percival Lowell.
Was Pluto Planet X?
The discovery of another planet was exciting news to everyone, even if that planet took over two hundred years to travel around the Sun. When it was first discovered, astronomers thought it was about the same size as Earth. As more information about the planet was learned, the estimates of the planet’s size kept shrinking. The most recent estimates of the size of Pluto put it at about half the size of Mercury, the closest planet to the Sun. Other measurements of the light reflected from Pluto suggest that it is probably made of frozen methane gas. It is too small and light to account for all the movement in Neptune’s orbit caused by Planet X.
What Else is Out There?
Astronomers are making many new discoveries about the Solar System using more powerful telescopes on Earth and in space. Beyond the orbit of Neptune, at over fifty times the distance between the Earth and the Sun (the astronomical unit), a whole group of icy objects orbits the Sun. These objects are called the Kuiper Belt. It is larger than the asteroid belt between Mars and Jupiter, and consists of icy rocks and planetoids made of frozen gases.
What Is a Planet Anyway?
In 2005, a team of astronomers discovered an object in the Kuiper Belt that was the same size or larger than Pluto. It consisted of frozen gases and rock, and was probably heavier than Pluto. That created a dilemma for scientists. Just how many planets are there in the solar system? Are there eight, or nine, or even more? Astronomers decided on a definition of “planet” based on three questions: Does the object orbit the Sun? Does the object have enough gravity to form a spheroid? Is the object unique in its orbit as the largest body in its orbit?
Is Pluto a Planet?
Pluto qualifies under the first two questions. It orbits the Sun on its own, and it is the right shape. The third question is the problem for Pluto, the asteroid Ceres as the largest in the belt between Mars and Jupiter, as well as the other objects in the Kuiper Belt. The reason relates to the theories about how planets are formed. Larger objects have enough gravity to form a spheroid, and the spheroid tends to collect enough matter around it in its orbit, so that it is the most dense object in its orbit, sweeping the area of everything around it. Pluto fails the test, and it is now called a “dwarf planet.” It still has a few surprises, though, including at least four moons of its own, one of them first seen in 2011 with the Hubble Space Telescope. In 2015, the flyby of the New Horizons space probe will provide the first clear pictures of Pluto and its neighborhood.
Interested in finding affordable tutoring rates for your child’s academic needs? Learn more about how we are assisting thousands of students each academic year.
SchoolTutoring Academy is the premier educational services company for K-12 and college students. We offer tutoring programs for students in K-12, AP classes, and college. To learn more about how we help parents and students in Houston, TX visit: Tutoring in Houston, TX