Listen here [0:39m]:
What’s the facts:
Pluto was discovered in 1930 (accidentally) by Clyde W. Tombaugh in Arizona during a sky survey at the Lowell Observatory. It is composed primarily of rock and ice and is significantly smaller than the other 8 planets: approximately a fifth the mass of the Earth’s Moon and a third its volume. It is much smaller than any of the official planets and has been recently classified as a “dwarf planet“. This happened largely due to the resent discovery of a larger dwarf planet named Eris, by Dr. Michael Brown of the California Institute of Technology. Eris opened the possibility that there may be many bodies of similar size. Scientists decided voted to consider the planets’ differences in size, orbit, and location as a criteria for a new classification, with objects like Pluto and Eris belonging to a special category of Kuiper Belt objects referred to as dwarf planets (but there is clearly debate on that decision, see comment below!). Click here to learn more about Pluto’s new classification.
Original air date 23 June 2009.