There might be a ninth planet in the solar system after all, and it is not Pluto.
Two astronomers reported in January last year that they had compelling signs of something bigger and farther away — something that would satisfy the current definition of a planet, where Pluto falls short.
“We are pretty sure there’s one out there,” said Michael E. Brown, a professor of planetary astronomy at the California Institute of Technology.
What Dr. Brown and a fellow Caltech professor, Konstantin Batygin, have not done is actually find that planet, so it would be premature to start revising mnemonics of the planets.
In a paper published in the Astronomical Journal, Brown and Batygin lay out a detailed circumstantial argument for the planet’s existence in what astronomers have observed: a half-dozen small bodies in distant elliptical orbits.
What is striking, the scientists said, is that the orbits of all six loop outward in the same quadrant of the solar system and are tilted at about the same angle. The odds of that happening by chance are about 1 in 14,000, Batygin said.
A ninth planet could be gravitationally herding them into these orbits.
For the calculations to work, the planet would be at least an equal to Earth, and most likely much bigger:perhaps a mini-Neptune with a mass about 10 times that of Earth. That would be 4,500 times the mass of Pluto.
Alessandro Morbidelli of the Cote d’Azur Observatory in France, an expert in dynamics of the solar system, said he was convinced. “I think the chase is now on to find this planet,” he said.
Pluto, at its most distant, is 4.6 billion miles from the sun. The potential ninth planet, at its closest, would be about 20 billion miles away; at its farthest, it could be 100 billion miles away. One trip around the sun would take 10,000 to 20,000 years.
Morbidelli said a possible ninth planet could be the core of a gas giant that started forming during the infancy of the solar system; a close pass to Jupiter could have ejected it. Back then, the sun resided in a dense cluster of stars, and the gravitational jostling could have prevented the planet from escaping to interstellar space.
This article is an edited version of a piece that originally appeared in the New York Times
(Kenneth Chang, New York Times)
DID YOU KNOW?
Pluto, discovered in 1930 by Clyde Tombaugh, was originally considered to be the ninth planet from the Sun. Questions over its classification as a planet led the International Astronomical Union to formally define the word “planet.” One of the conditions was that a body must have “cleared the neighborhood around its orbit,” that is, it has become “gravitationally dominant,” and there are no bodies of similar size — apart from its satellites — in its proximity that are not under its gravitational influence. This is the only condition that Pluto doesn’t satisfy: it has therefore since been classified as a “dwarf planet.”