Astronomers Confident That Planet X Has Been Found: Holy Crap!
Astronomers may have actually found a huge new planet in our solar system.
Yes, process that for a moment. I’m not talking about another new exoplanet, I’m talking about IN OUR solar system. And (if the indirect evidence is correct) it wouldn’t be some rinky dink dwarf planet or even a decent-sized rocky planet like the Earth or Venus. Estimates put its heft at 10 earth-masses meaning it could be a gas giant, roughly on the scale of Neptune itself.
You’re probably thinking that such a planet would have to be quite distant to have gone unnoticed this long and you’d be right. Current predictions put it in a distant orbit so large that each trip ’round the sun would take 15,000 earth years. This isn’t a circular orbit however and the putative planet’s distance from the sun could vary from a huge 200 AU to a mind-bending 600-1200 AUs. To put that into perspective, Neptune is a relatively paltry 30 AUs from the sun (by definition, earth is 1 AU from the sun).
This latest bit of “Holy Shit” Astro news was just published in The Astronomical Journal. The two scientists, who may just become household names if this pans out, are respected planetary scientists, Konstantin Batygin and Mike Brown of the California Institute of Technology (Caltech) in Pasadena. You may already remember Brown’s name. He’s known as the Pluto Slayer since he was instrumental in showing that Pluto was just one of probably many dwarf planets in the Kuiper belt. This of course led to Pluto’s controversial loss of “Planet” status.
The most important question now is: how compelling is their evidence? The search for Planet X has been going on for decades ever since the orbits of Uranus and Neptune seemed anomalous enough to require another planet nearby tugging it. This led to the discovery of Pluto, but its anemic mass couldn’t account for the apparent gravitational tugging. Ironically, the weird orbits of Uranus and Neptune were eventually found to be completely…not weird. New, more accurate, calculations showed them to be behaving just as they should, obviating the need of a Planet X to explain them. The hunt for Planet X didn’t abate though and over the years there’s been many bits of evidence being heralded as “Planet X Has Been Found!!”. All or most of these have been dumped into the waste bins of Astro history. Most Astronomers now-a-days roll their eyes at new Planet X predictions so any serious astronomers need to dot their Is and cross their Ts to be taken seriously. This is exactly what Batygin and Brown appear to have done.
They ran super computer simulations for a year to try and explain the weird orbits of 6 dwarf planets beyond Neptune. These tiny icy worlds inhabit the Kuiper belt and are called Kuiper Belt Objects (KBOs). These little guys were arranged in unusual elliptical orbits that made little sense. Their closest approach to the sun (perihelion) were all near the plane of our solar system, called the ecliptic, and also all clustered together. The other ends of their orbits however were all over the place, tilted away from the ecliptic and apart from each other. This convergence of orbits could certainly spontaneously happen by chance but we’re talking something like a 0.007 percent chance of that happening. Only 1 in 15,000. Could a planet cause this to happen? That is exactly what their simulations tried to find out. What they found was that if a planet had the precise characteristics I described above, including a specific (anti-aligned) elliptical orbit, it could easily, albeit slowly, shepherd dwarf planets into the stable orbits we observe. Apparently, this anti-aligned orbit is important. That simply means that Planet X’s perihelion is on the opposite side of the sun as the perihelia of the 6 dwarf planets.
So how could such a big planet get so far out there? One hypothesis is that it formed near the other gas giants of our solar system billions of years ago. Our solar system was a wild and woolly place back then like a huge pool table. With planets often hitting each other, it’s not hard to imagine our planet X having a near miss with a planet like Jupiter and being gravitationally ejected from its environs. Normally, it would just continue and completely exit our solar system, but between 3-5 million years after the birth of the solar system, there could have been enough gas and dust in the outer solar system to provide sufficient drag to slow it down and settle it into a stable orbit far from the sun but still within our solar system.
So how excited should we be right now? I think a decent level of optimism and excitement is warranted. This seem clearly to be the best indirect evidence for Planet X that we’ve ever had. Their paper has already been peer-reviewed. Planetary dynamicist Alessandro Morbidelli at the Nice Observatory in France went over the paper and considers their argument “pretty solid”. So much so that he said that he is “quite convinced by the existence of a distant planet.”
On the other hand, another planetary dynamicist, Hal Levinson is a little more skeptical. He believes that even though the weird aligned orbits were probably created by something out there, the origin of the planet involving the drag-inducing gas sounds like a “low-probability” event.
As compelling as this evidence is though, no one will be fully satisfied until astronomers can produce a picture with a small blob of light on it and say “See this? This is Planet X”. Unfortunately, finding Planet X with our premier telescopes like Hubble or Keck would be incredibly difficult. They certainly have the resolution to detect it but their field of view is too small to make the search practical. Fortunately there is a powerful enough telescope with a wide enough field of view. This is the Japanese-owned Suburu telescope in Hawaii. With its light gathering ability and field of view 75 times that of Keck, it could certainly produce that blob of light we need. Batygin and Brown are looking now but even with the large chunks of sky they can record each night it could take 5 years for the champagne corks to pop.
So cross your fingers and start playing the waiting game.