Ode to Pluto
HEMA VIJAY
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Discovered in 1930, and named after the Roman god of the underworld, Pluto has now been demoted to the "dwarf planet" status.
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Pluto is the only known heavenly body that rotates in synchrony with the orbit of its satellite.
PHOTO: AFP
NASA MONTAGE: Planetary images taken by spacecraft.
You would have heard about it by now. Yes, Pluto is no longer considered a planet. It is to be called a "dwarf planet" henceforth. Delegates of the 26th General Assembly of the International Astronomical Union (IAU) who met took this stunning decision on August 24, 2006, in the Czech capital Prague.
The IAU has also put forward a new definition for planets. To be considered a planet under the new nomenclature, the heavenly body must be big enough to have been pulled into a round shape by its own gravity. Planets must also dominate their neighbourhood, effectively clearing out other rubble in their path.
So, just why has Pluto been demoted? "While Pluto is round, it does not dominate its neighbourhood. It goes into the orbital space of Neptune pulled by Neptune's gravitational force," explains Dr. P. Iyamperumal, director, Tamil Nadu Science and Technology Centre, Chennai. Pluto also shares its space in the outer solar system — the Kuiper Belt — with numerous other icy objects. Apart from its moon Charon, Pluto's companions include object UB313, popularly known as Xena and Xena's moon Gabriella.
Pluto is different
Even in the past, Pluto's status had remained shaky and was always considered a peculiar planet. For instance, Pluto is the only known heavenly body that rotates in synchrony with the orbit of its satellite. So, unlike the earth and our moon, Pluto and Charon continuously face each other. Discovered in 1930, and named after the Roman god of the underworld, Pluto has an icy surface composed of nitrogen and methane and weighs just a fifth of the weight of our moon.
So, from now on, the rocky worlds of the inner solar system — Mercury, Venus, Earth and Mars, and the gas giants of the outer system — Jupiter, Saturn, Uranus and Neptune will comprise the planets in our solar system, while Pluto, Xena and Ceres (the largest rocky body orbiting the sun between Mars and Jupiter) are to be called "dwarf planets". Smaller objects orbiting the sun such as asteroids and comets will be called `small solar system bodies'.
A rose called by any name would smell just as sweet; likewise, this change in classification is not going to affect the forces operating in the universe, excepting for the species of homo sapiens on Planet Earth, who will now have to redo all their planetary models.
When Pluto was discovered
Pluto was officially labelled the ninth planet by the International Astronomical Union in 1930. It was the first and only planet to be discovered by an American, Clyde W. Tombaugh. The path toward its discovery is credited to Percival Lowell who funded three separate searches for "Planet X". Lowell made numerous unsuccessful calculations to find it, believing it could be detected from the effect it would have on Neptune's orbit. Dr. Vesto Slipher, the observatory director, hired Clyde Tombaugh for the third search and Clyde took sets of photographs of the plane of the solar system (ecliptic) one to two weeks apart and looked for anything that shifted against the backdrop of stars. This systematic approach was successful and Pluto was discovered on February 18, 1930. Pluto is actually too small to be the "Planet X" Percival Lowell had hoped to find.
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