Alinda asteroid
A dynamical group of asteroids in 3:1 resonance with Jupiter.
The Alinda asteroids form a dynamic group defined by a semi-major axis near 2.5 AU and orbital eccentricities typically ranging from 0.4 to 0.65. Their orbits are shaped by Jupiter’s 3:1 orbital resonance, which steadily increases their eccentricity until a close pass by an inner planet disrupts the resonance. Many Alindas have perihelia that bring them very close to Earth’s orbit, leading to repeated close encounters roughly every four years, thanks to a near 1:4 resonance with Earth.
This resonance can create persistent observational challenges: if an Alinda is poorly positioned during a close approach—such as near the Sun in the sky—that unfavorable geometry may last for decades. For instance, the asteroid 1915 Quetzálcoatl was observed only once between 1985 and 2010. On the other hand, the frequent, relatively close passes of some Alindas make them excellent targets for Earth-based radar studies. Examples include 4179 Toutatis, 6489 Golevka, and 2019 MO, which impacted Earth in June 2019.
The group’s dynamic age is linked to how far their eccentricity has evolved. Younger members, with eccentricities around 0.30 to 0.34, stay mostly within the main asteroid belt, ranging from 1.7 to 3.4 AU from the Sun. Older members, like 8709 Kadlu with eccentricities between 0.465 and 0.475, cross Mars’s orbit and are nudged by close approaches to Jupiter, Mars, and Earth. The oldest Alindas, with eccentricities from 0.57 to 0.75, cross Earth’s orbit. The most extreme is 3360 Syrinx, with an eccentricity of 0.7, giving it a dynamically short life expectancy.
- Namesake
- 887 Alinda
- Discoverer
- Max Wolf
- Discovery year
- 1918
- Semi major axis
- about 2.5 AU
- Eccentricity range
- approximately 0.4 to 0.65
- Jupiter resonance
- 3:1
- Earth near resonance
- 1:4
Lore & Background
The group is named after 887 Alinda, discovered by Max Wolf in 1918. 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 between 1.7 and 3.4 AU from the Sun. Older members, such as 8709 Kadlu, have eccentricities between 0.465 and 0.475 and cross the orbit of Mars; Kadlu makes approaches close enough to Jupiter, Mars, and Earth to be gravitationally nudged. The oldest members, with eccentricities between 0.57 and 0.75, cross the orbit of Earth. 3360 Syrinx is the most eccentric of the Alinda group with an eccentricity of 0.7 and has a dynamically short life expectancy.
Reader's Guide
The Alinda asteroids are notable for their dynamical evolution and observational challenges. Because some Alindas have perihelia very close to Earth's orbit, they make repeated relatively close approaches to Earth at nearly four-year intervals, making them good subjects for study by Earth-based radar. Examples include 4179 Toutatis and 6489 Golevka, as well as 2019 MO, which impacted Earth in June 2019. However, if an Alinda asteroid happens to be in an unfavorable position for viewing at the time of its close approach—for instance, at a small elongation from the Sun—this situation can persist for decades. As of 2010, the Alinda asteroid 1915 Quetzálcoatl had been observed only once since 1985. The group's members span a range of dynamical ages, from young objects that remain mostly in the asteroid belt to old, highly eccentric objects that cross Earth's orbit and have short dynamical lifetimes.
Did You Know?
- The namesake of the group is 887 Alinda, discovered by Max Wolf in 1918.
- The 3:1 resonance with Jupiter steadily increases the orbital eccentricity of Alinda asteroids.
- 3360 Syrinx is the most eccentric Alinda asteroid, with an eccentricity of 0.7.
Frequently Asked Questions
What is the Alinda asteroid group?
The Alinda asteroids are a dynamical family defined by a semi-major axis hovering around 2.5 AU and eccentricities that typically fall between 0.4 and 0.65. They are named after the prototype member, 887 Alinda, which Max Wolf identified in 1918.
How does Jupiter shape the Alinda asteroids' orbits?
Jupiter's 3:1 mean-motion resonance pumps up each Alinda's eccentricity over time. That growing stretch eventually drives the asteroid into a close encounter with an inner planet, which breaks the resonance and resets the cycle.
Why do Alinda asteroids keep swinging near Earth?
Many Alindas have perihelia that dip close to Earth's orbital distance, and a near 1:4 commensurability with Earth means they return to that region roughly every four years. This produces a recurring pattern of close flybys rather than a single one-off event.
What makes Alinda asteroids tricky to track observationally?
Because their orbits are so elongated, an Alinda can sit at a poor elongation or be lost in solar glare right when it should be easiest to spot. That positional bad luck, combined with the four-year return cadence, can leave astronomers with long gaps between useful observations.
Why is the Alinda group considered important in asteroid dynamics?
It serves as a textbook case of how a single planetary resonance—Jupiter's 3:1—can systematically reshape a population of small bodies over time. Studying the Alindas helps modelers understand how resonant pumping and subsequent planetary encounters drive long-term orbital evolution in the inner asteroid belt.
More in Notable Asteroids, Part 4 1-24
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