# Change in orbit when mass is doubled

• I
Muu9
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What happens to the once-circular orbit of a satellite when it's planet's mass suddenly doubles?
A satellite is orbiting a planet in a circular orbit. The planet's mass doubles instantly. What happens to the orbit of the satellite?

I think it would move to an elliptical orbit with major axis equal to the old radius and a minor axis equal to either 1/2 or sqrt(2)/2 times the old radius. I'm leaning toward the latter. What do you guys think?

Homework Helper
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What do you guys think?
I think you should do the maths!

• topsquark and Filip Larsen
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I think it would move to an elliptical orbit with major axis equal to the old radius and a minor axis equal to either 1/2 or sqrt(2)/2 times the old radius. I'm leaning toward the latter. What do you guys think?
Nothing would happen*. An object's orbital velocity is independent of its mass.

*As long as we are treating the star as not being affected by the planet's gravity.

Edit: Whoops, I misunderstood the question. The satellite's orbit would obviously change. Exactly how I'm uncertain at the moment.

Last edited:
• topsquark and vanhees71
Gold Member
Nothing would happen*. An object's orbital velocity is independent of its mass.
But here it is clearly stated it is the massive object that is doubling mass. And technical all mass changes would in principle have some effect, but since the satellite is not given mass I assume the OP question aim for a simple solution that does not involve reduced mass.

• topsquark and PeroK
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But here it is clearly stated it is the massive object that is doubling mass. And technical all mass changes would in principle have some effect, but since the satellite is not given mass I assume the OP question aim for a simple solution that does not involve reduced mass.
Oh wow, how did I misunderstand the question so badly?? I've edited my post.

• PeroK
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