A seven-member team appointed by the International Astronomical Organization, the IAU, agreed among themselves on the new definition of a planet: "Any body that orbits a star and is not itself a star, or that itself does not orbit a large planet, and is large enough to appear approximately spherical in shape "
Next week, with a simple vote by a show of hands, during an astronomical meeting, the Earth can go from a member of a family of nine planets to a member of a family of a dozen bodies, with a large number more bodies lined up, and more that have yet to be discovered.
A seven-member team appointed by the International Astronomical Organization, the IAU, agreed among themselves on the new definition of a planet: "Any body that orbits a star and is not itself a star, or that itself does not orbit a large planet, and is large enough to appear approximately spherical in shape ".
The draft proposal was submitted on Tuesday, August 16, and the debates will continue until August 22, in an open debate at a meeting in Prague. Two days later, by a majority of at least one person from among the members of the IAU, this will also be the official scientific determination.
Within this definition, most objects whose mass exceeds 51 thousand kilograms, and whose diameter is about 800 kilometers will qualify to be considered planets, unless they are moons in themselves. As we already posted yesterday, this decision will elevate the asteroid Ceres and Pluto's moon Charon to the rank of planets, since Ceres is almost spherical and Pluto and Charon can be described as a double planetary system. The 12th planet will be the object 2003 UB313, nicknamed Xena, one of the many beyond-Neptune objects floating around the edge of the solar system.
Not everyone agrees on the principle of the spherical shape. "It's not what you think of when you think of a planet," said Michael Brown, a Caltech astronomer who co-discovered Xena. "We don't think about things that are a thousandth the diameter of the Earth."
The discovery of Xena beyond the orbit of Pluto, about three years ago, caused a headache for scientists. Astronomers estimated that it was at least 2,400 kilometers in diameter - larger than Pluto, but still smaller than any of the other eight planets.
Some even then wanted to set a new definition for the term "planet". "If nothing is decided," the serious gathering will turn into a meeting. We must change the ridiculous situation, according to which Pluto meets the definition of a planet, while UB313 is not a planet." says Ivan Williams, an astronomer at Queen Mary University of London.
Williams chaired a previous committee of the IAU, which was supposed to define the planets, but its discussions reached an impasse last November. "People came with preconceived ideas about what a planet should be, expressed them out loud, and no one changed their minds," said committee member Alan Bos, an astronomer at the Carnegie Institution in Washington, in an interview with the website of the journal Nature. Opinions were divided between three different definitions: a planet orbiting a star, and in addition; Any object that is over 2,000 kilometers in diameter; Very massive objects, so gravity will make them round; Or any object that dominates its area, in space.
Following the impasse, the union appointed a new committee chaired by astronomer and historian Evan Gingrich from Harvard University. The group gathered on June 30 for two days at the Mitzpe in Paris. "We reached a conceptual convergence already at the end of the first day," says panel member Richard Binzel, of MIT.
The committee decided that the definition is based on gravity, something that makes scientific sense. According to Binzel, most physicists supported this direction.
In order to emphasize that the trans-Neptunian objects are different from the other planets, the committee proposed to declare a subcategory of planets called "plutonic" - planets that take more than 200 years to orbit the Sun, which includes Pluto, Charon and Xena.
The number of planets will increase and increase as more trans-Neptunian objects are discovered. After hooking up, even more asteroids will be tested. Such a change may upset generations who grew up on the term "nine planets". "I'm concerned about what will happen if the public accepts it," says astronomer Ron Akers, president of the IAU.
Binzel believes there are ways around the problem. "I would expect my children to remember the eight classic planets, to know that Ceres is a planet in the asteroid belt, and that there is a large collection of planets beyond Neptune, of which Pluto is the first.
It is estimated that it will not be easy for the committee members to convince their fellow astronomers. "There will be a long queue of people who will ask for the microphone and express their protest, so there is a chance that no decision will be made," members of the committee estimate. "That's the scariest thing," Binzel said, adding: "It's a very good compromise and it's time to move on."
Drafting and editing: H. J. Glykasm, translations and technical writing
