Questions: Research for Non-Scientific Purpose

[BuddingAuthor]

Hi All, I Am Looking for a bit of information, as you might note my name i am At the moment attempting to write a book, and am researching for said novel, although it is Sci-Fi/Fantasy in Genre.

 

For The Field of Astrophysics I am asking all those with knowledge of or theories on the behavior of gravity well when, or more importantly the plausibility of two same sized masses (eg. Two Earth Sized Planets) existing in the same gravity well without collision and at a close enough range so that their atmosphere's can at some points join, even if this is not possible at such a close range information on two same or very similar mass planetoids existing in orbit of each other.

 

My second question is what effects would the introduction of such a mass to say earths gravity well have have on the tidal flow ie. how much higher would they become if such a a thing happened.

 

thank you for all your feedback, anything is greatly appreciated, i hope this is the right place to put this thread thanks again

 

Sorry If My Sheer Idiocy offends, and if i have broken the rule about speculations etc, as i believe i will get, answers more on topic in this section of your forums, thank you

[Mr Skeptic]

Sounds dangerous. The atmosphere is much thinner than people might think, such a close encounter would result in friction not just from the atmospheres but more so from tidal/gravitational effects. Passing so close to each other could easily result in one of the planets being ejected from orbit, or perhaps even shredded. I would think the gravitational effects would be much nastier than the mixing of even a rather poisonous atmosphere.

[swansont]

You might want to read up on the Roche limit

http://en.wikipedia.org/wiki/Roche_limit

 

For identical planets, at d = 1.26R the tidal attraction will match the self-gravity, i.e. the planet can't be held together by gravity alone. That's without spinning.

 

The earth's radius is 6400 km, and the atmosphere less than 100 km, which means it extends to about 1.01R. Doesn't look plausible for earth-sized planets.

[BuddingAuthor]

so to make it plausible the satelite would have to be smaller then the earth and with a larger atmosphere? the mathmatics in these things confound my brain i try and try and try but always come out with the wrong bits and peices its rather annoying really you see i want a planetoid to be large enough that as it orbits they both have a day night cyclebut once every week or two there is a night twice as long as normal because the other mass blocks out the sun like a lunar eclipse kind of

[Mr Skeptic]

Hm, what if you make your planet be a moon of a jupiter-sized gas giant, and have the gas giant eclipse the sun every so often?