Astronomers are brawling again about a ninth planet


There’s a new act starting in the most melodramatic real-life space opera of our time.

Once our solar system was home to nine simple planets. Then that number was unceremoniously and controversially reduced to eight. Now, years later, there’s new evidence that we could really be in a nine-planet system after all.

Before we go any further, I’ll go ahead and burst the optimistic bubble of all you justified Pluto lovers out there: The adorable, be-hearted, blue-skied world remains a demoted dwarf planet.

Instead, Pluto’s nemesis is at the center of things once again: Caltech astronomy professor Mike Brown. If you don’t know him by his legal name, perhaps his Twitter handle @PlutoKiller may provide some hints regarding his notoriety.

Astronomers are brawling again about a ninth planet

Planet Nine could be a gas giant similar to Neptune or Uranus.

Caltech/R. Hurt (IPAC)

Brown and his former student-turned-colleague Konstantin Batygin co-authored a paper published online Wednesday by the Astronomical Journal that lays out evidence for an unseen giant planet lurking in the distant reaches of our solar system. Scientists have been discovering dwarf planets beyond Pluto for several years now and hints of a far larger, unseen “Planet X” have gained attention and a bit of mockery along the way.

The pair originally set out to debunk the hidden planet theory but had a hard time explaining it away.

“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there,” Batygin said in a statement. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete.”

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The researchers believe the planet, which they’ve dubbed “Planet Nine,” has a mass about 10 times that of Earth and follows a strange elongated orbit through the outer solar system. It lies about 20 times farther from the sun than Neptune, far enough out that a single trip around our star might take 10,000 to 20,000 years. Talk about a long winter.

The problem with the prospect of re-adding a (new and different) ninth planet to our solar system is that no one has actually seen Planet Nine yet. It’s yet to be viewed through any kind of telescope or other imaging method. Instead, Brown and Batygin hypothesize in their paper that the very strange orbital behavior of some smaller objects in the outer solar system are all pointing to the presence of a large planet exerting its gravitational influence in the neighborhood.

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Almost as soon as the paper was published, skeptics sought to temper the excitement.

“I couldn’t be more pleased about what’s happening,” NASA’s Jim Green said in the video below, referring to the reaction to the paper. “It is not, however, the detection of a new planet. It’s too early to say with certainty that there is a so-called ‘Planet X’ out there.”

Astrophysicist Ethan Siegel laid out his own response to the evidence for Planet Nine.

“The possibility is tantalizing, and unlike the previous iterations of a ‘ninth planet’ that have hit the news, there’s actually some good evidence this time,” he wrote. “But is the evidence good enough to believe it? Not even close; not yet.”

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Brown and Batygin agree, which is why they’re openly encouraging everyone to help actually locate and image the purported planet.

“I would love to find it,” Brown said. “But I’d also be perfectly happy if someone else found it. That is why we’re publishing this paper. We hope that other people are going to get inspired and start searching.”

There’s nothing more exciting than the search for a new world. I just hope Pluto can forgive us.