Xena, another small celestial entity in the outer reaches of the solar system, was being considered as an addition to the solar system’s planets. But it now appears, in a surprising but perhaps inevitable development, Pluto is being decertified as a planet instead. This is what the New York Times says in Wednesday’s edition: “The new definition offered yesterday would set up a three-tiered classification scheme with eight ‘planets’; a group of ‘dwarf planets’ that would include Pluto, Ceres, Xena and many other icy balls in the outer solar system; and thousands of ‘smaller solar system bodies,’ like comets and asteroids. The bottom line, said the Harvard astronomer Owen Gingerich, chairman of the Planet Definition Committee of the union, is that in the new definition, ‘Pluto is not a planet.’”
A long argument may ensue over whether Pluto is really a kind of planet or not. Reuters reports a slightly different interpretation:
“Under the new definition, schoolchildren will be relieved to know that, just as they were taught, Pluto will remain a planet. But it would also fall into a newly created category called plutons, which are distinguished from classical planets in that they take longer than 200 years to orbit the sun. Pluto would be joined in this new category by two other celestial bodies, Xena and Charon, while another, Ceres, would be known as a dwarf planet.”
Another development of note is the recent claim that proof now exists for dark matter because of a galactic collision. A BBC science article describes the findings:
“The researchers have discovered what is effectively the gravitational signature of dark matter. This signature was created by dark matter and ordinary matter being wrenched apart by the immense collision of two large galaxy clusters.”
[illustration of Xena: NASA/AP]