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rfmcdonaldWikipedia calls the hypothetical planet announced by a Caltech team to possibly exist beyond Neptune's orbit "Planet Nine". The first article I was sent was National Geographic's coverage.
The paper mentioned, Batyagin and Mike Brown's "Evidence for a Distant Giant Planet in the Solar System", makes for interesting if technical reading. NPR, interviewing Brown, suggests that the existence of this planet explains quite a lot about the outer solar system.
At least one person, astronomer Alessandro Morbidelli quoted in the Washington Post, as saying that the evidence for this planet is much stronger than for other putative ninh planets. Brown, for his part, famous as the man who made Pluto a dwarf planet, has gone on the record as saying that this planet would definitely qualify.
Centauri Dreams and the Planetary Society Blog have more information about this world, the latter having links to relevant papers.
As described Wednesday in the Astronomical Journal, the gravitational signature of a large, lurking planet is written into the peculiar orbits of these farflung worlds. Called extreme Kuiper Belt Objects, the misbehaving bodies trace odd circles around the sun that have puzzled scientists for years.
It’s tantalizing evidence that a ninth large planet might live in the solar system, though the world hasn’t been detected yet.
“If there’s going to be another planet in the solar system, I think this is it,” says Greg Laughlin of the University of California, Santa Cruz. “It would be quite extraordinary if we had one. Fingers crossed. It would be amazing.”
The team calculated that the planet, if it’s there, would be about 10 times as massive as Earth, or roughly three times larger. That makes it a super-Earth or mini-Neptune—a type of planet the galaxy is incredibly efficient at assembling, but which has been conspicuously absent from our own neighborhood.
“This thing is on an exceptionally frigid, long-period orbit, and probably takes on the order of 20,000 years to make one full revolution around the sun,” says Caltech’s Konstantin Batygin, who is one half of the planet-sleuthing team.
The paper mentioned, Batyagin and Mike Brown's "Evidence for a Distant Giant Planet in the Solar System", makes for interesting if technical reading. NPR, interviewing Brown, suggests that the existence of this planet explains quite a lot about the outer solar system.
The first suggestion that something big might be affecting the orbits of distant, icy bodies came in 2014. An international team of astronomers announced that they'd discovered a new dwarf planet, nicknamed Biden, that stays even farther out than Sedna. They also noted a strange clustering in the orbits of these objects, and in the orbits of about a dozen others. Perhaps, they hypothesized, the gravity of some unseen planet was acting as a shepherd.
"They were pointing out that there was something funny going on in the outer solar system, but nobody could really understand what it was," says Brown. "Ever since they pointed it out we've been scratching our heads."
[. . . As Brown and Batyagin] studied the freaky way that these objects lined up in space, Brown says, they realized that "the only way to get these objects to line up in one direction is to have a massive planet lined up in the other direction."
What's more, this planet naturally explains why the dwarf planets Sedna and Biden have weird orbits that never let them come in close to the solar system. "This wasn't something we were setting out to explain," says Brown. "This is something that just popped out of the theory."
But there was one moment that turned Brown into a believer. Their computer simulations predicted that if this hypothetical planet existed, it would twist the orbits of other small bodies in a certain way. So Brown looked through some old data to see if any icy bodies had been discovered with those kinds of orbits — and, lo and behold, he found five of them.
"They're objects that nobody has really explained or tried to explain before," says Brown. "My jaw hit the floor. That just came out of the blue. Being able to make a prediction and having it come true in five minutes is about as fun as it gets in science."
At least one person, astronomer Alessandro Morbidelli quoted in the Washington Post, as saying that the evidence for this planet is much stronger than for other putative ninh planets. Brown, for his part, famous as the man who made Pluto a dwarf planet, has gone on the record as saying that this planet would definitely qualify.
"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."
Brown notes that the putative ninth planet—at 5,000 times the mass of Pluto—is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets—a fact that Brown says makes it "the most planet-y of the planets in the whole solar system."
[. . .]
Brown, well known for the significant role he played in the demotion of Pluto from a planet to a dwarf planet adds, "All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found," he says. "Now we can go and find this planet and make the solar system have nine planets once again."
Centauri Dreams and the Planetary Society Blog have more information about this world, the latter having links to relevant papers.
