10 Most Iconic Alien Planets In Modern Doctor Who
8. Krop Tor
Appearing in 2006's The Impossible Planet/The Satan Pit, Krop Tor - also known as 'The Bitter Pill' - was an asteroid-like planet orbiting a black hole - a feat meant to be impossible.
Craggy and prone to earthquakes, Krop Tor was an intimidating locale. Established as a research post on the planet was Sanctuary Base 6, investigating its mysterious ability to stay in place whilst the universe around it was sucked into the black hole.
During one of the earthquakes, the TARDIS disappeared into a chasm - trapping the Tenth Doctor and Rose Tyler inside the Base.
Having burrowed ten miles down into the planet's barren surface, the Doctor and science officer Ida Scott uncovered the ruins of an ancient civilisation - and a trap-door leading to a seemingly bottomless pit.
Scaling the pit, Krop-Tor was discovered to be the prison of the Beast - a demon from before the universe's creation. Imprisoned on the planet, the technology used to hold the Beast was also keeping it from falling into the black hole. However, any attempt to free the creature would switch off the planet's gravity and it would be sucked into the void.
When the human explorers evacuated the crumbling world, the Doctor 'freed' the Beast and the planet was destroyed, with its prisoner falling into the black hole. Luckily, the Doctor managed to escape in his TARDIS - which had slipped through the cracks in Krop Tor and arrived at the prison.
Intergalactic Travel Advice: Danger of falling.