Planet Nine, a captured exoplanet? How B-grade sci-fi is that idea?

6 May 2016

There has been chatter in recent months about Planet Nine, a would-be planetary body lurking on the extreme far reaches of the solar system.

The hypothetical planet is so far away, its orbital period around the Sun is estimated at ten thousand years. By comparison, Pluto, the solar system’s best known dwarf, and outermost planet, completes a lap around the Sun in about two-hundred-and-forty-eight years.

But back to Planet Nine. Before even confirming the body even exists, astronomers are trying to figure out its origins. Wouldn’t that be easier once the planet is found? Whatever, some scientists believe it formed relatively close to the Sun, before being dispatched to the solar system’s outer reaches after a run-in with Jupiter.

Others, however, think Planet Nine is an exoplanet, a once rogue exoplanet possibly, that was captured by the Sun, after straying a little too closely to our solar system.

The final scenario sounds like a plot line from a B-grade sci-fi movie, and it seems to be comparably unlikely. Planet Nine could be an extraterrestrial invader. “Planet 9 may be an exoplanet in our own solar system,” said Gongjie Li, another astronomer at Harvard’s Center for Astrophysics whose recent modelling paper explores this very possibility, among others.

I’m not sure though I like the notion of Planet Nine being described as “a plot line from a B-grade sci-fi movie”, since it’s an idea I’ve been kicking around, as if it were a cosmic soccer ball, so to speak, in one of my sci-fi writing projects.

Originally published Friday 6 May 2016. Updated Friday 24 May 2024.