Terrestrial planets, gas giants and ex-Neptunian planets instead of just planets
A panel of experts who were asked to resolve the dispute about what is a planet and what is not a planet recommended that astronomers replace the word planet with other words.
The panel says that astronomers should stop using the term "planet" by itself, and instead, define certain types of planetary objects.
According to the recommendation, Earth and Venus (and probably also the planet Mercury and Mars, AB) terrestrial planets, Jupiter and Thebes will simply be called gas giants, and Pluto will be called a trans-Neptunian object.
The plan was emailed to all panel members on September 12, Nature magazine reported.
"Old habits are hard to kill"
The panel of 19 astronomers was assembled last year by the International Astronomical Union (IAU) and was required to find a solution to the dispute.
The division among astronomers over the definition of the planet intensified this year with the discovery of a distant object known as 2003 UB313, whose discoverers rushed to call it the tenth planet.
One of their arguments stemmed from the size of 2003 UB313 - it is as big as Pluto if not bigger. And if Pluto was recognized as a planet then 2003 UB313 must also receive such recognition.
Others claimed that the two objects - Pluto and 2003 UB313 belong to a group of icy bodies known as the Kuiper Belt itself, which surround the Sun at a distance of about 10 billion km.
Prof. Ewan Williams, chair of the panel and an astronomer at Queen Mary University of London, said the panel hopes to send the final version to the IAU for discussion within about two weeks.
However, others do not agree with the proposal. Alan Stern, of the Southwest Institute in Boulder, Colorado, says astronomers should use properties, not location, as a guideline when defining the type of planetary object.
In his view, objects like 2003 UB313 and Pluto should be called "ice dwarfs".
Jacqueline Mitton, an astronomy writer from Cambridge in the UK, suggested that the public and astronomers alike would reject the proposal. "Old habits don't die," she told the website of the journal Nature. "Committees can make statements but they can't always change things."
By the way, the term "extrasolar planet" will be reserved for objects orbiting bodies other than the Sun, according to the proposal.
