# How long could Miller's Planet remain in orbit [closed]

In Christopher Nolan's movie Interstellar, Miller's Planet is in orbit around a supermassive black hole affectionately (??) called Gargantua.

Miller's Planet orbiting Gargantua:

It is orbiting "at the cusp" of the black hole, in an orbit I presume to be very close to the "critical orbit" (which is the closest stable orbit to the black hole - inside this radius not even light can orbit stably). Kip Thorne specially designed Gargantua with a high spin so that Miller's Planet's orbit would be "stable".

But how stable exactly?

How much time would pass on the surface of the planet (don't forget relativistic time dilation) before Miller's Planet slipped inside this "critical orbit" and began is spiral into Gargantua?

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• I'm afraid this planet is a big science plothole - Thorne did what he could to make it more possible but it's still not. – Mithoron Jun 22 '15 at 15:10
• Obviously a group of white knights built a gravity manipulator to keep the devil trapped in a stable orbit around the planet. As long as some fool with a box doesn't free him, the planet is stable. – user16696 Jun 22 '15 at 17:35
• Wouldn't this question be better for Worldbuilding SE? – Nit Jun 22 '15 at 18:50
• I don't think so, but maybe Physics? – Jim2B Jun 22 '15 at 18:50

Orbit of this planet wouldn't be stable because it would have to cross accretion disk or paths of particles falling from it into hole - it would cause significant drag and cause deorbitation - it would fall into the black hole.

Another thing is that this photo seems inaccurate: being near photon sphere, planet would be much closer - in similar distance as inner edge of disk, probably too small to be seen from such perspective.

Even black hole itself doesn't look right for the scenario the movie creators cherry picked to have extreme time dilation on the planet - very high rotation rate of the black hole was needed and light coming from the disk would be distorted differently from what they used in the movie - a much lower rotation rate version of simulation of the black hole.

• I assumed the critical orbit was outside the outer portions of the accretion disk but this may or may not have been a good assumption :) – Jim2B Jun 22 '15 at 17:08
• Thorne does say near the end of ch. 17 of The Science of Interstellar that "since Miller's planet is the closest anything can live stably, without falling into Gargantua, the entire accretion disk should be outside the orbit of Miller's planet." But he goes on to say they fudged the visual depiction so we wouldn't get super-close up views of the black hole early on in the movie when they visited Miller's planet, saving the really close up views for the climax. As for drag, wouldn't it depend on how sharply the density of the disk drops off as you pass its inner edge? – Hypnosifl Jun 22 '15 at 18:33
• @Hypnosifl Yes, it would, and how far form it is the orbit. Planet would have to cross the plane of the disk at least in two places or even could be totally in plane, which wouldn't be surprising. – Mithoron Jun 22 '15 at 20:12

It may happen never. Given enough speed the planet might have a stable orbit.

Risks are:

• The black hole increases its mass by continually swallowing matter making the black hole heavier and therefore make before stable orbits unstable
• Debris around the black hole slows down the planet

Neither is terribly likely, as the space is mostly empty.