The Black sheep of the family
134340 Pluto. Strange as it may seem, this is the new name assigned to Pluto, following the controversial decision of the International Astronomical Union (IAU) to strip it of the planetary status it has enjoyed, ever since its discovery in 1930. On August 24, 2006, Pluto, the last planet to join the heavenly pantheon, became the first to leave it.
For those with a sound understanding of solar astronomy and planetary motion in general though, this decision does not come as a surprise. The astronomers have always been skeptic about the classification of Pluto as a planet and with time, the developments in the field of astronomy, have only strengthened their suspicions.
Size: Neptune, the eight planet was actually, first discovered on paper. Basically, they followed the trend set by the previous planets in terms of mass and orbital parameters and predicted the position of the next planet and when the telescope was turned to that point, they found Neptune. Pluto however, is a complete misfit. Its size is too small to fit into the picture. As a matter of fact, Pluto is even smaller than several satellites of the solar system, including ours.
This also makes Pluto incapable of clearing its immediate neighbourhood and defining its territory in some sense. The term ‘clearing the neighbourhood’ refers to a situation in which the gravitational influence of the object is strong enough to cause all the small bodies around it to either accrete with it or be thrown away into another orbit. This is considered an important step in the process of planet formation and the fact that Pluto has not cleared the Kuiper belt objects such as Plutinos, is an important condition that Pluto does not satisfy in the IAU’s new definition of a planet.
Orbit: The orbit of Pluto is highly eccentric while all other planets have near circular paths of revolution. Infact the eccentricity of the orbit is so high that for some period of time during a plutonian year, (which is roughly 248 earth years) Neptune, and not Pluto is the farthest planet from the sun. In addition to this, the orbit of Pluto is highly inclined (upto 17 degrees) above the ecliptic plane (an imaginary flat plane in which all other planets revolve round the sun).
The last nail in Pluto’s coffin came with the discovery of several trans Neptunian objects like Quaoar and Sedna which satisfied the expected orbital parameters better than Pluto. The only factor that could still have saved Pluto was the fact that it has an atmosphere and a satellite. But with the discovery of Eris, which has similar surface composition as Pluto and a satellite as well, all its hopes were laid to rest. There was nothing special about Pluto anymore.
Does this change of status mean anything more than the fact all the 6 th standard NCERT textbooks will now need some modification?
It certainly raises a question regarding what Pluto really is. For the time being though, the astronomers have settled this issue by assigning Pluto the status of a ‘dwarf planet’. Infact the astronomers had to come up with a new term ‘dwarf planet’ in order to accommodate for heavenly bodies like Pluto. Currently, only 3 objects Eris, Pluto and Ceres (the largest asteroid) bear the status of a dwarf planet.
More importantly, there can be no example, as vivid as this one, to demonstrate the fact that science is self correcting.
In any case, all those who have some sort of an attachment with Pluto can express their discontent and petition against this decision by logging onto www.ipetitions.com/petiton/planetprotest , a forum setup by the rebel astronomers (and there are lots of them) to lodge their protest against the IAU.
Watchout for the new developments in this field. Classifications are changing so thick and fast, that by the time you read this, there could be several other members of the solar system added to the list of dwarf planets.
Some interesting facts about Pluto
1) Pluto was discovered in 1930 by Charles Tombaugh at the Lowell Observatory. Apart from being the name of a Roman god, the christening of this heavenly body was also intended to evoke the initials of Percival Lowell who played the pivotal role in its discovery.
2) It has 3 satellites viz. Charon, Nix and Hydra. The size of Charon is so nearly equal to that of Pluto that they are often considered to be a binary system. (As a matter of fact their centre of mass lies outside either of the two bodies)
3) It was earlier mistaken that Mercury and not Pluto is the smallest planet of the solar system because the astronomers observed both Pluto and its satellite Charon as a single entity.
3) When Pluto is close to the sun, the Nitrogen in its atmosphere (that had solidified when it was away from the sun) sublimates and produces a cooling effect similar to the one produced when sweat evaporates from our skin. Due to this effect, known as the ‘antigreenhouse effect’, the surface of Pluto is 10K cooler than expected.
4) Pluto shares several features in common with comets. Infact solar winds are gradually blowing its surface away into space.
5) After reaching Saturn, the controllers of Voyager 1, could have continued on their journey towards farther planets, which would have brought them closer to Pluto. Instead, they opted for analyzing the newly discovered atmosphere of Saturn’s moon, Titan. This required the probe to take a flyby around Titan and the consequent change in trajectory ended their hopes of reaching any other planet. However, on the 19 th of January this year, NASA launched the spacecraft ‘New Horizons’, to visit Pluto.
