Gravitational capture occurs when one object enters a stable orbit around another (typically referring to natural orbits rather than
orbit insertion 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, an orbital maneuver is called a ''deep-space maneuver (DSM)''.
When a spacec ...
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, specifically either an irregular moon if permanently captured, or a ...
turns a star-orbiting asteroid into an
irregular moon if captured permanently, or a
temporary satellite. 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) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf.
Rogue planets may originate from ...
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) a ...
of other planets in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
, 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 List of hypothetical Solar System objects, hypothetical ninth 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 obj ...
in the 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 ...
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 (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...
exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...
s orbits are misaligned with their stars and a few even in the
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 ...
.
Rogue planet
A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf.
Rogue planets may originate from ...
s can theoretically be formed in this way, and planets could lose their moons this way.
Tidally detached exomoons 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 by which stars lose some mass over their lives. Mass loss can be caused by triggering events that cause the sudden ejection of a large portion of the star's mass. It can also occur when a star g ...
could also cause planets to escape orbit and go rogue.
See also
*
Exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...
*
Ballistic capture
Ballistic capture is a low energy method for a spacecraft to achieve an orbit around a distant planet or moon with no fuel required to go into orbit. In the ideal case, the transfer is Ballistics, ballistic (requiring zero Delta-v) after launch. I ...
References
Astronomical events