In a bizarre example of science fiction art imitating real-life space science, the latest Doctor Who episode dealt with a secret planet in our solar system around the exact same time that real news spread of “planetary mass object” hidden at the edge of the Kuiper Belt.

A forthcoming academic article from the Astronomical Journal will explore how and why the orbits of objects in the Kuiper Belt are the way the are. In order to account for the “warped” orbits of objects in the Kuiper Belt — including dwarf planets like Pluto — this article postulates that something as big as a planet must be influencing gravity. “According to our calculations, something as massive as Mars would be needed to cause the warp that we measured,” Kat Volk, one of the article’s authors, said.

Meanwhile, on Saturday, the first of the two-part season 10 finale of Doctor Who revisited the concept of a secret planet in our solar system called Mondas. First introduced in the 1966 Who episode “The Tenth Planet,” Mondas was considered to be sort of a twin of the planet Earth, and home to the cyborg villians, the Cybermen. In the latest episode, “World Enough and Time,” the renegade Lime Lord Missy discovers that a certain immense colony starship actually originates from the planet Mondas. Before the planet is identified, our own solar system is briefly scanned.

Missy finds a secret planet that isn't so secret on 'Doctor Who.'

In 1966, Mondas was called “The Tenth Planet,” because, of course at that time, Pluto was decades away from being down-graded to a dwarf planet. In Doctor Who lore, Mondas originally hung out in the orbits between Mars and Venus. Eventually, the Cybermen fitted Mondas with its own propulsion system, meaning the planet’s orbit could basically be anywhere.

The map that Missy glances at seems to put Mondas somewhere in the inner planets. But who knows? Maybe the Cybermen moved Mondas moved again, and that theoretical new Kuiper Belt planet could be teaming with cyborgs from our distant past.


The next issue of the Astronomical Journal will be published on July 1. The second half of the Doctor Who season finale, in which more about Mondas will likely be revealed, airs on the exact same day.