Monday, April 12, 2010

New Method of Classifying Planets Proposed

Image comment: Artist's drawing depicting the dwarf planet Haumea, with its tow moons. The body has a prolonged shape that puzzles astronomers
Image credits: A. Feild (Space Telescope Science Institute)

The way the International Astronomical Union (IAU) goes about defining planets is a topic that many are uncomfortable with. A large proportion of all astronomers in the organization do not agree with the definitions by which the IAU decided which space object is classified as a planet, and which as a dwarf planet. This was made very obvious in 2006, when the organization voted – with only a few members in attendance – that Pluto was a dwarf planet, and not a real, full-size one. Now, experts propose a new method of defining what planets are, Technology Review reports.

The international scientific community has been trying to determine the best possible way of defining a planet for many ears, but most propositions on how to do that have thus far fallen short of their original goal. For instance, experts cannot classify an object on a planet based only on size, as throughout the Universe, size varies widely among planets. The IAU currently employs three criteria. The first is that the body needs to be orbiting the Sun, the second is that it must have sufficient mass to have formed a nearly spherical shape, and the third is that it needs to have cleared its orbit.

Pluto was deemed to be meeting the first two criteria, but not the third, because it passes through the orbit of Neptune. But critics say that, if Pluto was not deemed a planet because of this, then neither should Neptune be considered a planet, as it also failed the third criteria. Australian National University in Canberra expert Charles Lineweaver and Marc Norman decided to investigate the matter on their own, and the team now proposes a new approach to defining what a planet is. They basically suggest that any body which is not potato-shaped, and which has a diameter of more than 200 kilometers, can be considered a dwarf planet.

The problem with their approach is the fact that this definition raises the number of dwarf planets in the solar system considerably, while at the same time making the asteroid Vesta – a potato-shaped space rock much larger than 200 kilometers – a cosmic oddity. This method of defining space objects again puts Pluto as the number one dwarf planet, but it's unlikely to sit well with those who want to see the body established to its former “glory”. The main issue here remains elevating interest in this type of research, as more often than not, this translates into increased funding for this type of studies.