Results 1 to 9 of 9

Thread: Solar system with backward orbiting planet possible?

  1. #1
    Join Date
    Jun 2018
    Posts
    17

    Solar system with backward orbiting planet possible?

    Is it possible for a solar system to have a planet that orbits backwards compared to the other planets in that solar system?

  2. #2
    Join Date
    Jun 2005
    Posts
    14,269
    Quote Originally Posted by paulel View Post
    Is it possible for a solar system to have a planet that orbits backwards compared to the other planets in that solar system?
    Yes, its possible, but unusual. Basically, it requires an interstellar planet to enter a solar system and then get captured by exchanging energy with another planet in that system.
    As above, so below

  3. #3
    Join Date
    Jan 2004
    Posts
    7,269
    Not sure about orbiting "Backwards" but I had heard that Venus rotates backwards on it's axis compared to the other planets, but I could be wrong

  4. #4
    Join Date
    Aug 2013
    Posts
    587
    Google says there are 2.

    'planet with opposite orbit'

    The exceptions the planets with retrograde rotation are Venus and Uranus. Venus's axial tilt is 177, which means it is rotating almost exactly in the opposite direction to its orbit. Uranus has an axial tilt of 97.77, so its axis of rotation is approximately parallel with the plane of the Solar System.

  5. #5
    Join Date
    Jun 2005
    Posts
    14,269
    I think its worth noting that the OP was asking about retrograde orbits, not rotation.
    As above, so below

  6. #6
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,695
    I just Googled "Regrograde moons" and it appears there are quite a few, including Triton, the largest moon of Neptune. So not planets, exactly but certainly retrograde orbits are possible. Generally retrograde moons are small and probably captured.
    Wikipedia.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  7. #7
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
    Posts
    49,856
    There are also retrograde asteroids.

    Minor planets with orbital inclinations greater than 90 (the greatest possible is 180) orbit in a retrograde direction. As of March 2018, of the near-800,000 minor planets known, there are only 99 known retrograde minor planets (0.01% of total minor planets known).[13] In comparison, there are over 2,000 comets with retrograde orbits. This makes retrograde minor planets the rarest group of all. High-inclination asteroids are either Mars-crossers (possibly in the process of being ejected from the Solar System) or damocloids. Some of these are temporarily captured in retrograde resonance with the gas giants.[14]
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  8. #8
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    22,089
    Quote Originally Posted by paulel View Post
    Is it possible for a solar system to have a planet that orbits backwards compared to the other planets in that solar system?
    It should be a very unlikely thing to happen. You can imagine a system like ours with a Jupiter-like gas giant and a swarm of Mars-sized inner planets. Imagine that interactions of the inner planets kick one of them out to the gas giant, and it has a "lucky" gravitational interaction with it similar to the Ulysses probe that went into an elliptical orbit over the Sun's poles. Imagine that in a later encounter the planet again interacts with the gas giant in a similar way that puts it close to the ecliptic plane, but with a backwards orbit (note: this orbit would initially take it *very* close to its Sun). Imagine then that this planet interacts with an inner planet near its periastron, and reduces its apogee enough to prevent more interactions with the gas giant for a long time. In that case, you would have a planet orbiting backwards. You can see that to do it would require a lot of lucky chances to all happen.
    Forming opinions as we speak

  9. #9
    Join Date
    Mar 2004
    Posts
    3,185
    The answer is definitely yes if retrograde is defined with respect to the stars's rotation. The Rossiter-McLaughlin effect - changes in the mean Doppler shift of a star's light as pieces of it are alternately covered and uncovered by a transiting body such as a planet - has shown that there are planets whose orbits are not just polar, but almost exactly retrograde to the host star. Th WASP serve has turned up about 5 of these. Explanations usually center on interactions among massive planets in that system (keeping in mind that we may not be in a position to detect the non-transiting planets in most systems).

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •