Astronomers have reported that they have compelling information leading to the existence of a body in the solar system that meets the requirements of a planet. The body is bigger and farther away than Pluto, but the astronomers have not actually found the planet. The New York Times reports:
In a paper published in The Astronomical Journal, Dr. Brown and Dr. 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, Dr. Batygin said.
The discovery of the world that Brown and Batygin refer to in The Astronomical Journal simply as “Planet 9” began in 2003, with the discovery of a far more modest object named Sedna. A dwarf planet even smaller than Pluto, Sedna is a Kuiper Belt object (KBO), like Pluto one of a vast band of icy, rocky objects that surround the solar system beyond the orbit of Neptune. Brown was part of the team that found Sedna too, and if anything made the new world remarkable, it was its extreme distance from the sun—one that has it completing a single orbit in 11,400 years, compared to Pluto’s 248.
But something else was strange about Sedna as well—or at least about the company it keeps. In the years that followed, astronomers discovered five other KBOs whose closest approach to the sun (or perihelion) matches Sedna’s almost perfectly, both in distance and in the angle of the orbit relative to the horizon of the solar system.
It’s not the first time people have claimed to have evidence of such a planet lurking on the edge of our galactic neighborhood. The debate about this world’s existence has been going on for the last century. In 1905, Percival Lowell predicted a Planet X existed beyond Neptune; his calculations actually led to the discovery of Pluto, which was too small to be what Lowell suspected. Now a century later, researchers at the California Institute of Technology say they have the best argument yet for Planet X. “If you say, ‘We have evidence for Planet X,’ almost any astronomer will say, ‘This again? These guys are clearly crazy.’ I would, too,” study author Mike Brown, a planetary scientist at Caltech, told Science. “Why is this different? This is different because this time we’re right.”