Gravitational capture occurs when one object enters a stable orbit around another (typically referring to natural orbits rather than

orbit insertion Orbit insertion is the spaceflight operation of adjusting a spacecraft’s momentum, in particular to allow for entry into a stable orbit around a planet, moon, or other celestial body. This maneuver involves either deceleration from a speed in exc ...

of a spacecraft with an

orbital maneuver In spaceflight, an orbital maneuver (otherwise known as a burn) is the use of propulsion systems to change the orbit of a spacecraft. For spacecraft far from Earth (for example those in orbits around the Sun) an orbital maneuver is called a ' ...

s).

Asteroid capture Asteroid capture is an orbital insertion of an asteroid around a larger planetary body. When asteroids, small rocky bodies in space, are captured, they become natural satellites. All asteroids entering Earth's orbit or atmosphere so far have been n ...

turns a star-orbiting asteroid into an

irregular moon In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular sat ...

if captured permanently, or a

temporary satellite A temporary satellite is an object which has been captured by the gravitational field of a planet and thus has become the planet's natural satellite, but, unlike irregular moons of the larger outer planets of the Solar System, will eventually either ...

. Capture events explain how satellites can end up with retrograde orbits or rotation. Planetary capture of a

rogue planet A rogue planet (also termed a free-floating planet (FFP), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary-mass, therefore smaller than fusors (stars and brown dwarfs) and without a h ...

by a star or other planet is also theoretically possible, but , none has yet been directly observed. Because the angle of encounter is somewhat random, such an event would likely leave the captured planet in an orbit outside the

orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) an ...

of other planets in the solar system, possibly in a retrograde orbit. Planetary capture has been proposed one mechanism that could explain the unusual orbit of the hypothesized

Planet Nine Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbit t ...

in the Earth's solar system. (

Planetary migration Planetary migration occurs when a planet or other body in orbit around a star interacts with a disk of gas or planetesimals, resulting in the alteration of its orbital parameters, especially its semi-major axis. Planetary migration is the most l ...

is a competing explanation.) Planetary capture (possibly planet swapping with neighboring stars) has been proposed as one explanation for why an unusually high fraction of

hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

s orbit their stars in a retrograde direction.

Ejection

The opposite process, ejection from orbit, can occur through orbital instability or one or more encounters with another passing object ( perturbations), eventually putting the object on a

hyperbolic trajectory In astrodynamics or celestial mechanics, a hyperbolic trajectory or hyperbolic orbit is the trajectory of any object around a central body with more than enough speed to escape the central object's gravitational pull. The name derives from the fa ...

Rogue planet A rogue planet (also termed a free-floating planet (FFP), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary-mass, therefore smaller than fusors (stars and brown dwarfs) and without a h ...

s can theoretically be formed in this way, and planets could lose their moons this way.

Tidally detached exomoon Tidally detached exomoons, also known as orphaned exomoons or ploonets, are hypothetical exoplanets that were formerly exomoons of another planet, before being ejected from their orbits around their parent planets by tidal forces during planetary m ...

s have been proposed to explain some astronomical observations, but {{as of, 2023, lc=yes none have been observed. Severe

stellar mass loss Stellar mass loss is a phenomenon observed in stars. All stars lose some mass over their lives at widely varying rates. Triggering events can cause the sudden ejection of a large portion of the star's mass. Stellar mass loss can also occur when a st ...

could also cause planets to escape orbit and go rogue.

References

Astronomical events

Ejection

See also

References