The Alinda asteroids are a
dynamical group
In mathematics, a dynamical system is a system in which a Function (mathematics), function describes the time dependence of a Point (geometry), point in an ambient space. Examples include the mathematical models that describe the swinging of a ...
of
asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
s with a
semi-major axis
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
of about 2.5
AU and an
orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...
approximately between 0.4 and 0.65.
Minor planet groups/families
The namesake is 887 Alinda, discovered by Max Wolf
Maximilian Franz Joseph Cornelius Wolf (21 June 1863 – 3 October 1932) was a German astronomer and a pioneer in the field of astrophotography. He was the chairman of astronomy at the University of Heidelberg and director of the Heidelberg-Kà ...
in 1918.
These objects are held in this region by the 3:1 orbital resonance
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
with Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
(2.502 AU), which results in their being close to a 1:4 resonance with Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
(2.520 AU). An object in this resonance has its orbital eccentricity steadily increased by gravitational interactions with Jupiter until it eventually has a close encounter with an inner planet
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 "Solar S ...
that breaks the resonance.
Some Alindas have perihelia very close to Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's orbit, resulting in a series of close encounters at almost exactly four-year intervals, due to the 1:4 near resonance.
One consequence of this is that if an Alinda asteroid happens to be in an unfavorable position for viewing at the time of its close approach to Earth (for instance, at a small elongation from the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
), then this situation can persist for decades. Indeed, as of 2010, the Alinda asteroid 1915 Quetzálcoatl had been observed only once since 1985.
Another consequence is that some of these asteroids make repeated relatively close approaches to Earth, making them good subjects for study by Earth-based radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
. Examples are 4179 Toutatis and 6489 Golevka, as well as 2019 MO, which impacted Earth in June 2019.
Dynamic age
The 3:1 resonance with Jupiter causes a repeating growth in the eccentricity of the asteroid's orbit. Dynamically young members have an eccentricity ranging from about 0.30 to 0.34 staying mostly in the asteroid belt ranging 1.7–3.4 AU from the Sun.3360 Syrinx
3360 Syrinx (originally designated 1981 VA) is an Apollo and Mars crosser asteroid discovered in 1981. It approaches Earth to within 40 Gm three times in the 21st century: 33 Gm in 2039, 40 Gm in 2070, and 24 Gm in 2085.
On ...
is the most eccentric of the Alinda group with an eccentricity of 0.7 and the orbit has a dynamically short life expectancy.
List of members
See also
* Amor asteroid
The Amor asteroids are a group of near-Earth asteroids named after the archetype object 1221 Amor . The orbital perihelion of these objects is close to, but greater than, the orbital aphelion of Earth (i.e., the objects do not cross Earth's orb ...
* Apollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth ...
* Aten asteroid
The Aten asteroids are a dynamical group of asteroids whose orbits bring them into proximity with Earth. By definition, Atens are Earth-crossing asteroids . The group is named after 2062 Aten, the first of its kind, discovered on 7 January ...
References
{{Small Solar System bodies
*
Asteroid groups and families