Mystery in the Outer Solar System

One Giant Planet X or Actions of Little Worlds?

The outer solar system is a mysterious place. No, it isn’t filled with monsters and ghosts. Not that kind of mysterious. Instead, it’s a mystery because we haven’t explored even a tiny percentage of it. Sure, the New Horizons spacecraft is heading out through it and has explored Pluto. But, it’s one tiny spacecraft and space is very big. There ARE worlds out there, as we know from previous ground-based discoveries of Sedna, Eris, Quaoar, and so on. And, there have been hints of something big out there—really big. Is it a large world? Or could it be something else?

Gravity tells a Tale of Sedna’s Orbit

The main way we “know” something is out there is because there’s a gravitational perturbation affecting the known worlds in the Kuiper Belt. Whatever it is, it’s causing those orbits to change a tiny bit, and that’s measurable by telescopes here on Earth. Planetary scientist Mike Brown of CalTech suggested that it’s a big Planet X, some monster world with enough mass and gravity to tug on orbits of smaller worlds. That’s entirely possible. But, it hasn’t been observed yet. So, that’s a bit of a problem.

What if the perturbations weren’t from some giant world out there, but a combination of gravitational interactions of smaller bodies on each other? That’s the idea behind a theory that seeks to explain some planetary oddities that exist far from the Sun. Take Sedna, for example. It orbits out at a distance of 12 billion km (8 billion miles) from the Sun, and it’s part of the solar system, but appears separated in its orbit from the other worlds out there.

Astronomers at the University of Colorado suggest that, instead of some large body disturbing the orbit of dwarf planet Sedna and other worlds, there may be another explanation. They calculated that the orbits of Sedna and other worlds may be perturbed it and other worlds jostling against each other and space debris in the outer solar system. Interactions (although not necessarily collisions) could affect orbits.

Studying the Orbit of Sedna

The orbits of places such as Sedna, which are often referred to as “detached objects”, have large, circular orbits that don’t really get close to Jupiter or Neptune, and it’s not clear how they got to the outer solar system. Orbital dynamics of outer solar system objects (that is, the motions they experience as they orbit) comprise a lot of computer simulations going on right now. One outcome suggests that small-scale interactions of bodies in the solar system can act on their orbits (and even on larger bodies). And those kinds of interactions may well have affected Sedna’s orbit, circularizing it and making it “detached”. It also means that smaller objects “out there” may still be affecting the orbits of worlds such as Sedna, and giving the appearance of something “really big” doing the perturbing.

Of course, the theory needs to be backed up with observations of those distant places, or even one big world. So far, all planetary scientists have is the tantalizing clue that gravitational tugs are affecting orbits. It could be one big place or a lot of little ones.

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