Kirkwood gaps are gaps or dips in the distribution of main belt
asteroidthumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]] measuring about across. Photograph taken in 1997 by the [[NEAR Shoemaker]] probe.Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are...
s with
semi-major axisIn geometry, the semi-major axis is used to describe the dimensions of ellipses and hyperbolae.- Ellipse :The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
(or equivalently their
orbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
), as seen in the histogram below. They correspond to the location of
orbital resonanceIn celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
s with
JupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth that of the Sun but is two and a half times the mass of all of the other planets in our Solar System combined. Jupiter is classified as a gas...
.
For example, there are very few asteroids with semimajor axis near 2.50
AUAn astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....
, period 3.95 years, which would make three orbits for each orbit of Jupiter (hence, called the 3:1 orbital resonance). Other orbital resonances correspond to orbital periods whose lengths are simple fractions of Jupiter's.
Kirkwood gaps are gaps or dips in the distribution of main belt
asteroidthumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]] measuring about across. Photograph taken in 1997 by the [[NEAR Shoemaker]] probe.Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are...
s with
semi-major axisIn geometry, the semi-major axis is used to describe the dimensions of ellipses and hyperbolae.- Ellipse :The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
(or equivalently their
orbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
), as seen in the histogram below. They correspond to the location of
orbital resonanceIn celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
s with
JupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth that of the Sun but is two and a half times the mass of all of the other planets in our Solar System combined. Jupiter is classified as a gas...
.
For example, there are very few asteroids with semimajor axis near 2.50
AUAn astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....
, period 3.95 years, which would make three orbits for each orbit of Jupiter (hence, called the 3:1 orbital resonance). Other orbital resonances correspond to orbital periods whose lengths are simple fractions of Jupiter's. The weaker resonances lead only to a depletion of asteroids, while spikes in the histogram are often due to the presence of a prominent
asteroid familyAn asteroid family is a population of asteroids that share similar orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions...
.
The gaps were first noticed in 1857 by
Daniel KirkwoodDaniel Kirkwood was an American astronomer.Born in Harford County, Maryland, he was graduated in mathematics from the York County Academy in York, Pennsylvania in 1838...
, who also correctly explained their origin in the orbital resonances with Jupiter.
More recently, a relatively small number of asteroids have been found to possess high eccentricity orbits which do lie within the Kirkwood gaps. Examples include the
Alinda familyThe Alinda asteroids are a group of asteroids with a semi-major axis of about 2.5 AU and an orbital eccentricity approximately between 0.4 and 0.65. The namesake is 887 Alinda, discovered by Max Wolf in 1918....
and the
Griqua familyThe Griqua asteroids are a group of asteroids in the Main Belt orbiting the sun between 3.1 and 3.27 AU. Asteroids in this group have eccentricities greater than 0.35. The group derives its name from the asteroid 1362 Griqua....
. These orbits slowly increase their eccentricity on a timescale of tens of millions of years, and will eventually break out of the resonance due to close encounters with a major planet.
The most prominent Kirkwood gaps (see diagram) are located at mean orbital radii of:
- 2.06 AU
An astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....
(4:1 resonance)
- 2.5 AU (3:1 resonance), home to the Alinda family
The Alinda asteroids are a group of asteroids with a semi-major axis of about 2.5 AU and an orbital eccentricity approximately between 0.4 and 0.65. The namesake is 887 Alinda, discovered by Max Wolf in 1918....
of asteroids
- 2.82 AU (5:2 resonance)
- 2.95 AU (7:3 resonance)
- 3.27 AU (2:1 resonance), home to the Griqua family
The Griqua asteroids are a group of asteroids in the Main Belt orbiting the sun between 3.1 and 3.27 AU. Asteroids in this group have eccentricities greater than 0.35. The group derives its name from the asteroid 1362 Griqua....
of asteroids
Weaker and/or narrower gaps are also found at:
- 1.9 AU (9:2 resonance)
- 2.25 AU (7:2 resonance)
- 2.33 AU (10:3 resonance)
- 2.71 AU (8:3 resonance)
- 3.03 AU (9:4 resonance)
- 3.075 AU (11:5 resonance)
- 3.47 AU (11:6 resonance)
- 3.7 AU (5:3 resonance)
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