In a discussion elsewhere about binary planets, it came the question.

How near can a planet like Earth (maybe Earth itself) be to another planet like Earth before both of them tearing apart due to tidal forces?

In other words: Which is the Roche limit for Earth, if it were orbiting (another) Earth?

  • $\begingroup$ Why didn't you directly looked at the Wikipedia page? It seems you know what you are asking for. So I can't imagine a reason on why the first source on the web would not be able to answer your question. $\endgroup$ – Py-ser Nov 25 '14 at 5:47
  • $\begingroup$ Wikipedia gives generalities as "Rigid" and "Fluid" but not an actual distance for Earth near Earth. It gives not even a single figure for Moon near Earth. $\endgroup$ – Envite Nov 26 '14 at 11:00
  • $\begingroup$ So, this does not answer your question, did I understand correctly? $\endgroup$ – Py-ser Nov 26 '14 at 13:43
  • $\begingroup$ @Py-ser True, it does not answer it, because Earth is not exactly rigid (no celestial body is). $\endgroup$ – Envite Dec 1 '14 at 10:07

According to wikipedia, the roche limit for an object with the same density as the Moon would be around 10,000 kilometres. Since the density of the Earth is about 166% of that of the Moon, if you don't take the atmosphere, or oceans into account, then the binary planets could be much closer to each other. However, when you take into account the oceans, and atmosphere, it would probably be a lot further away.

  • $\begingroup$ Nice answer. Consider our own moon's effect on the oceans. $\endgroup$ – dotancohen Nov 24 '14 at 17:54
  • $\begingroup$ How much? I want to know which is the distance for such a Roche Limit, please. $\endgroup$ – Envite Nov 26 '14 at 10:59

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