Does a Massive Planet Lurk in the Outer Solar System?

Could there be a massive planet well beyond the orbit of Pluto? Unfortunately, this "extraordinary" claim is based on rather "ordinary" evidence.

There's a planet, possibly four times the mass of Jupiter, composed of hydrogen and helium, potentially with a system of moons, hiding in the furthest-most reaches of the solar system. That's according to two University of Louisiana scientists anyway.

No, the sun's evil twin Nemesis hasn't been found, and the pretend purveyor of doom, Planet X, hasn't been spotted either. This is a different kind of world, possibly as complex and interesting as Jupiter, but living in a region of space that is as mysterious as the world itself.

Dubbed "Tyche," this hypothetical planet is causing a small buzz. If it does exist, the confirmed number of planets in our solar system would grow back to nine (sorry Pluto, you're still a dwarf planet) and Jupiter would be relegated to second fiddle.

What's more, the International Astronomical Union (IAU) might need to create a new planetary class for this object, as it would have most likely formed around another star, only to have been kidnapped by the sun's gravity eons ago.


Oort Cloud Hide-and-Seek

Astrophysicists John Matese and Daniel Whitmire from the University of Louisiana at Lafayette arrived at this theory after analyzing comets passing through the inner solar system. They found that many of the comets had strange orbits, contradicting widely accepted cometary theories.

Matese and Whitmire have been trying to track down Tyche since 1999 and it's their belief that there must be a massive world crawling through the outer Oort cloud.

The Oort cloud is a hypothetical volume of space encapsulating our entire solar system and is thought to be the birth place of the long-period comets we see speed through our solar system. It's unimaginably vast, well beyond our heliosphere, up to around 1 light-year distant. That's a quarter of the way to the next star.

Comets are thought to have formed in the Oort cloud since the birth of the solar system and, occasionally, they get disturbed by the gravity of a passing star, causing them to plunge toward the sun, like a high diver jumping off the platform toward the pool below.

But say if Tyche is living in the Oort cloud, stirring things up? That might be causing the oddities spotted in some long-period comets.

"Ordinary Evidence"

Interestingly, as a gas giant of this size is so massive, it would be emitting some heat as it slowly cools since being formed (in a similar fashion to Jupiter), so it could give away its location if its infrared emissions are detected. The researchers are therefore looking to analyze data from NASA's Wide-Field Infrared Survey Explorer (WISE) to find Tyche.

Before we get too excited about the possibility of an imminent historic announcement, it turns out that the majority of the astronomical community isn't particularly confident about Tyche's existence.

Ned Wright, principal investigator for the WISE mission, told Discovery News that the theory behind Tyche is based on "ordinary evidence for an extraordinary claim."

Regardless, as WISE continues to catalog a vast number of infrared sources throughout the cosmos, the mission will keep an eye open for any oddities in the Oort cloud.

"Matese and Whitmire have recently extended the mass range of their prediction down to [the mass of Jupiter] and that is getting a bit hard for WISE to detect at 0.5 light-years from Earth, so we will have to do a careful analysis of lots of faint sources to be sure we haven't missed something," Wright said.

"It should take another couple of years before we can be sure."

Comet Statistics

Dave Jewitt, professor at UCLA, is no stranger to solar system detective work and isn't overly enthusiastic about Matese and Whitmire's theory either.

"This claim is based on the statistics of comet arrivals and the argument that there is an unexpected concentration of comets that results from an unseen planet far beyond the planetary region," Jewitt explained.

According to Jewitt, new claims about the reasons behind comet clustering appear every few years, and while this clustering is interesting, observational bias could be leading us to believe there is something causing Oort cloud asymmetries (i.e. clusters of comets), rather than it being a real phenomenon.

"For example, most people live in the northern hemisphere, so it is easier to detect comets on that side of the earth than on the other, southern side," he said. "The result is that we have biased, noisy comet counts that make discerning comet excesses very tricky."

Jewitt would rather wait until WISE data can prove or disprove Tyche's existence, rather than drawing too many conclusions from comet statistics.

"People have short memories and this is one of those recurrent stories that seems to be attractive to the web surfing population again and again," Jewitt said. "A distant Jupiter is certainly on the cards, in terms of what we know about the structure, origin and evolution of the solar system, but that's because we are largely ignorant about the huge space in the solar system much beyond Neptune."

"We can't rule it out yet. But WISE should have the data to soon rule it out, or to show that it's real."

Image: Is that Tyche? Credit: NASA, edit by Ian O'Neill, Discovery News.