21
$\begingroup$

I was just wondering if it were possible to A) Orbit the moon and earth B) To orbit any two celestial bodies really?

$\endgroup$
30
$\begingroup$

The simple answer is yes.

The more complicated answer starts to look at types of orbit.

  • You could have a figure-8 orbit, which has centres around both.
  • You could have an orbit that goes around the centre of mass of the two bodies (in the case of Earth - Moon this is a point within the Earth, but for Pluto-Charon it lies between the two bodies) - this is likely to be a much wider orbit
  • You could have a Lagrange orbit, where you are orbiting a gravitational point because of the two bodies, but not actually going round them (odd edge case of the word 'orbit')

Some may be stable, others not. In fact the free-return trajectory for Apollo 8, 10 and 11 is an unstable version of the first one. It is a figure-8 that goes out past the moon and comes back. But only once.

Have a read of @TildalWave's post for more info on resonant orbits.

And an example I love - the Apollo 12 fragment (from Wikipedia):

enter image description here

$\endgroup$
  • 1
    $\begingroup$ So in a lagrange orbit it'd be like playing Tug-Of-War with an evenly matched team, keeping the body central? $\endgroup$ – Josh R Mar 25 '16 at 14:01
  • 7
    $\begingroup$ Most orbits of these kinds are not very stable. The earth-moon system had a temporary satellite in an orbit around the center of mass in 2006-2007: en.wikipedia.org/wiki/2006_RH120 $\endgroup$ – Rob Mar 25 '16 at 15:38
  • 9
    $\begingroup$ Fascinating graphic! Where is it from, or how is it made? What is "The" Apollo 11 fragment? Inquiring minds want to know! $\endgroup$ – uhoh Mar 25 '16 at 17:00
  • 3
    $\begingroup$ Note that an object orbiting the Earth needs to be inside the Earth's Hill sphere, or it risks being lost into a solar orbit instead. This means that it can't orbit much further than about 3.88 times farther than the Moon, which might not be a large enough orbit to treat the Earth-Moon system as a point mass concentrated at a single point. $\endgroup$ – Michael Seifert Mar 25 '16 at 19:38
  • 1
    $\begingroup$ Yup. It came as a surprise to astronomers when they figured out what it was. $\endgroup$ – Rory Alsop Mar 29 '16 at 18:10
2
$\begingroup$

Yes it's possible, and known ... at Pluto. What are officially called the (four known) smaller moons of Pluto are actually orbiting the center of mass formed by Pluto and its large moon Charon, which is outside both Pluto and Charon.

Wikipedia includes an animation of all the known moons orbiting Pluto. The small moons are all much farther away from the center of mass than Pluto and Charon are, so they "see" the larger binary mass as approximately a single point.

$\endgroup$
  • 1
    $\begingroup$ From this perspective, any planet with two or more moons counts. The outer ones orbit around the planet and the inner ones. $\endgroup$ – Steve Linton May 27 at 14:49
  • $\begingroup$ The primary feature at Pluto, of course, is that the CM about which everything orbits is in space not the largest body. $\endgroup$ – Oscar Lanzi May 27 at 15:19
-2
$\begingroup$

Because of the inherent instabilities of this type of orbit, to keep a satellite in orbit around the Earth Moon system. The clever manipulation of light pressure from the Sun could possibly be used to compensate for the instabilities of this type of orbit to keep it within the Hill Limit.

$\endgroup$
  • 6
    $\begingroup$ I didn't down vote, but this answer is a bit too short and unsupported to be considered a good Stack Exchange answer. If you can explain better why an orbit around the Earth-Moon system would always be unstable, that would be better, and adding a source (a link or a reference) would be even better! Welcome to Stack Exchange! Have a look around and get a better feel for what kinds of answers tend to be well receeived. $\endgroup$ – uhoh Sep 29 '18 at 6:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.