There might be a ninth planet in the solar system after all — and it is not Pluto.

Two astronomers reported Wednesday 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 Brown, a professor of planetary astronomy at the California Institute of Technology.

What 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 based on the observation of a half-dozen small bodies in distant elliptical orbits that all loop outward in the same quadrant of the solar system and are tilted at about the same angle.

Batygin said the odds of that happening by chance are about 1 in 14,000, which means a ninth planet could very well be gravitationally herding these bodies into these orbits.

Chad Trujillo, an astronomer at Hawaii’s Gemini Observatory, said Brown and Batygin present a compelling case that a ninth planet is out there.

Trujillo, Brown and other astronomers have discovered a number of key objects in the Kuiper Belt, the ring of icy debris that extends outward from Neptune’s orbit, about 2.8 billion miles from the sun, to a bit less than twice Neptune’s orbit, about 5 billion miles. He said historically there has been a lot of speculation about whether such a planet lies beyond the Kuiper Belt.

“But it was all based on minimal evidence,” he said. “For the first time, a real credible scientific study is predicting it.”

The last time a planet was discovered from a prediction, based on the orbit of Uranus, was Neptune in 1846, he said.

It was Trujillo and Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, who hinted at the ninth planet in a 2014 paper.

Trujillo and Sheppard, both of whom earned their Ph.Ds at the University of Hawaii, noted that several Kuiper Belt objects had similar orbital characteristics, and they laid out the possibility of a planet disturbing the orbits of these objects. “It was the best explanation we could come up with,” Trujillo said.

But the particulars of their proposed planet did not explain what was in the sky, Brown said.

“The theorists didn’t really take it seriously,” he said. “They figured it was all some observational effect. The observers didn’t take it seriously, because they figured it was all some theoretical thing they couldn’t understand.”

Still, the peculiarities of the orbits appeared genuine.

To offer enough gravitation to herd the various objects, 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.

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.

“We have pretty good constraints on its orbit,” Brown said. “What we don’t know is where it is in its orbit, which is too bad.”

Alessandro Morbidelli of the C ote 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.

Trujillo said he, Sheppard and University of Hawaii astronomer David Tholen will be looking for the planet. He said it could be found tomorrow or take anywhere from five to eight years, considering how much sky must be scanned.

A large telescope now under construction in Chile, capable of surveying the entire sky, should help accelerate the discovery, if it has been found yet in the next few years, he said.

This would be the second time that Brown has upended the map of the solar system.

In January 2005, he and Trujillo discovered a Pluto-size object, now known as Eris, in the Kuiper Belt. The next year, the International Astronomical Union placed Pluto in a new category, “dwarf planet,” because in its view, a full-fledged planet must be the gravitational bully of its orbit, and Pluto was not.

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.

If the planet exists, it would easily meet the definition of planet, Brown said.

“There are some truly dominant bodies in the solar system and they are pushing around everything else,” Brown said. “This is what we mean when we say planet.”