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.
These objects are held in this region by the 1:3
orbital resonance with
Jupiter, which results in a 4:1 resonance with
Earth. 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 that breaks the resonance.
Some Alindas have
perihelia very close to
Earth's orbit, resulting in a series of close encounters at almost exactly four-year intervals, due to the 4:1 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), then this situation can persist for decades. Indeed, as of
2004, the Alinda asteroids
(3360) 1981 VA and
1915 Quetzálcoatl had not been observed since
1985, and
2608 Seneca had not been observed since
1994.
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. Examples are
4179 Toutatis and
6489 Golevka.Some Alinda asteroids are shown below:
