Pluto-The controversial planet

Pluto has been our favorite planet since 2006. The reason why I wrote this blog is because NASA is ready to explore the planet and study it closely through its mission New Horizons. So before we get to know about this mission, let’s first get to know about Pluto.

HISTORY:

Pluto was discovered on February 18, 1930 in the Kuiper Belt. Kuiper belt is a ring of bodies beyond Neptune. Originally Pluto was considered as the ninth planet in solar system. But studying its size, mass, density etc. the International Astronomical Unit (IAU) defined the term “planet”. The definition goes as-

“planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has cleared its neighbourhood" of smaller objects around its orbit.”

 According to this definition, Pluto could not be classified as a planet and hence was reclassified as a “dwarf planet” in 2006.

Although it is a dwarf planet compared to other eight planets, it is the second most massive dwarf planet known.

PLUTO’S COMPOSITION AND ITS SURFACE:

Pluto is primarily made of ice and rock. It is relatively small- about one-sixth the mass of the moon and one-third of its volume. Pluto’s icy surface is made of 98% Nitrogen. Methane and traces of carbon monoxide is also present.

PLUTO’S ORBIT:

Pluto orbits Sun at a distance of 4.4-7.4 billion kilometers. It has rather an unusual orbit. It is usually farther from Sun than other planets. However, due to eccentricity of its orbit, it is closer than Neptune for 20 years out of its 249 years orbit. Pluto crossed Neptune’s orbit on January 21, 1979; made its closest approach to Sun on September 5, 1989 and remained within Neptune’s orbit until February 1999. This will not occur again until September 2226. Pluto’s rotation period is of six days. Light from sun takes 5.5 hours to reach Pluto’s surface!

PLUTO’S CONTROVERSY:             

Till 2006, Pluto was considered as the ninth planet of the solar system. But after IAU defined the term “planet”, it was excluded and reclassified as a dwarf planet. But now the team of scientists working on New Horizons mission has proposed a new definition which will again include Pluto as a planet. The new definition proposed is as follows-

“A planet is a sub-stellar mass body, that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by triaxial ellipsoid regardless of its orbital parameter.”

The team has decided to propose this new definition, after studying the planet closely.

Even if IAU decides to accept this new definition, it will take some time to become official. Till then Pluto will just have to wait.