Science Updates

Pluto is no longer in the club of planets, but downgraded to a dwarf planet and a plutonian object.

The voting in the 2006 International Astronomical Union (IAU) General Assembly last Thursday nailed the fate of our remote icy neighbor.

Reluctant Pluto-supporters asked people to “honk if Pluto is a planet”. Anyhow, textbooks now need to be swiftly revised for this coming academic year.

The new criteria of planet are:
1. Orbiting a star,
2. Having enough gravitational force to make itself into a sphere, and
3. Having cleared away objects of comparable size from its orbit.

Pluto, discovered by Clyde Tombaugh in 1930, failed to fulfill the last criteria and was downgraded to be a dwarf planet.

It is joined by Charon, its previous moon, and become the first double planet in the solar system.

One of the main worries for accepting Pluto is its neighbors. “Pluto has too many friends”, said an astronomer.

UB313, nicknamed Xena, was discovered three years ago. It’s a planet further away from the sun but a little bit bigger than Pluto.

Scientists worried that if they let in Pluto, then Xena and other small rubbles would also join the party.

According to the new definition, our solar system consists of eight planets and four dwarf planets: Ceres, between Mars and Jupiter, double planets Pluto and Charon, and UB313 (Xena). 

On Thursday next week (August 24), we would have 12 planets in the Solar System and many more objects could be qualified as planets in the universe, if astronomers agree on the new definition of planet.

International Astronomical Union (IAU) has spent two years to review the definition of a planet. According to the new proposal, the planet must:
- Be orbiting a star, but must not itself be a star, and
- Have a nearly spherical shape, resulted by its own gravitational pull.
The rigid mass and diameter requirement are transformed into the “roundness” criteria.

Apart from Pluto, three more objects have passed these requirements: Charon, UB313 nicknamed Xena and Ceres, between Mars and Jupiter.

A new term ”plutons” would also be coined. These are planets beyond Neptune, which take more than 200 years to orbit the Sun.

Textbooks would need to be re-written that ”Our Solar System has orbiting the sun in order of: Mercury, Venus, Earth, Mars Ceres, Jupiter, Saturn, Uranus, Neptune, and plutons Pluto, Charon and UB313.”

Charon is today categorized as a moon to Pluto, but recenly scientists found that Pluto and Charon are orbiting each other, being the first pair of twin planets in the Milky Way.

UB313 (Xena) is discovered last year and has at least 2,400 km in diameter, a bit larger than Pluto. It is one of the objects in the Kuiper belt in the outer region of the Solar System. 

Scientists worried if the new definition would lower the status of planet in public’s eyes. The heated debate has started in the astronomy meeting in Prague. On August 24, scientists will vote and decide the fate of Pluto and the picture of our children’s astronomy books.

External Link
> Planet Definition – International Astronomical Union (IAU)