Following the general meeting of the IAU in 2006, a new classification scheme was released for the various members of the solar system and
which was inspired by the 2003 discovery of Eris, a Kuiper belt object beyond the orbit of Pluto and which happened to be also larger than
Pluto by about 100 km. To be more specific, the three categories adopted where (1) planets, (2) dwarf planets and (3) small solar system
bodies.
Dwarf planets are similar to planets in the sense they orbit the sun and have sufficient mass so that gravitational forces lead to a generally
round shape but which have failed to clear their orbit of debris due to a lack of a dominating gravity. Using this definition, the solar system
is now characterized with eight (and not nine) planets, five dwarf planets (Pluto, Ceres, Iris, Makemake and Haumea) and various small solar
system bodies excluding satellites.
Three members of the asteroid belt (Vesta, Pallas, Hygieia) as well as over 40 trans-Neptunian objects (Orcus, Ixion, Huya, Varuna, Quaoar,
Sedna etc) are believed to eventually be classified as dwarf planets.
Note: Pluto has a history similar to that of Neptune in that it was discovered in 1930 by Clyde Tombaugh following
calculations by Percival Lowell. Pluto is quite unique in that it is smaller than our moon, has a "large" moon (Charon) whose diameter is more
than half of the parent planet and a very eccentric orbit which brings it inside Neptune's orbit at perihelion. Observation of Pluto is only
possible with a telescope due to its very low (14th) magnitude.
For an ephemeris of Pluto using the facilities of the Jet Propulsion Laboratory (NASA), click
here. Similarly, for Pluto's orbital
elements, click here.
Note: The field of view in the image below involves the twin Barnard dark nebulae
B92 and
B93 and where Pluto happened to be traversing through in the summer of 2010.
Please click on the image below to display in higher resolution (1200 x 850)