Koronis family
A large stony asteroid family with two younger subfamilies.
The Koronis family, sometimes called the Koronian or Lacrimosa family, is a large group of stony asteroids in the outer main belt. Its smallest-numbered member is 158 Koronis, which gives the family its name, while the largest known member, 208 Lacrimosa, measures roughly 41 kilometers across. The family formed at least two billion years ago when two larger bodies collided catastrophically. Though its members travel on independent orbits around the Sun, those orbits share similar semimajor axes, eccentricities, and inclinations; the asteroids themselves are not physically clumped together in space. However, the spin poles of several large members appear to be aligned. The family contains at least 5,949 members.
Within the Koronis family are two subfamilies. The Karin family formed much more recently, about 5.72 million years ago, from a catastrophic collision that destroyed the parent body. The other subfamily, Koronis(2), has 246 members and formed 15 million years ago from a non-catastrophic collision involving 158 Koronis.
On August 28, 1993, the Galileo spacecraft flew past 243 Ida, a member of this family, and captured an image of it along with its small moon Dactyl. That image appears in the composite picture on the right, labeled 243.
- Alternative names
- Koronian family, Lacrimosa family
- Fin designation
- 605
- Location
- outer region of the asteroid belt
- Largest member
- 208 Lacrimosa
- Diameter of largest member
- 41 km
- Number of members
- at least 5949
- Age
- at least two billion years
Lore & Background
The Koronis family is thought to have been formed at least two billion years ago in a catastrophic collision between two larger bodies. Its members travel in independent heliocentric orbits that share similar semimajor axes, eccentricities, and inclinations, though the asteroids themselves are not physically clustered in space. The spin poles of several of the large members appear to be aligned in space. The family contains two subfamilies: the Karin family, formed remarkably recently in a catastrophic collision that destroyed the parent body, with an estimated age of 5.72 million years; and the Koronis(2) family, with 246 members, formed 15 million years ago by a non-catastrophic collision with 158 Koronis.
Reader's Guide
The Koronis family holds significance as a well-studied asteroid family whose members provide insight into collisional evolution in the asteroid belt. Its age of at least two billion years makes it one of the older known families, while its two subfamilies—the Karin family and the Koronis(2) family—offer contrasting examples of recent disruption events. The Karin subfamily, formed only 5.72 million years ago, represents a very young catastrophic collision, whereas the Koronis(2) subfamily, at 15 million years old, resulted from a non-catastrophic impact. The alignment of spin poles among several large members suggests a common origin and possibly a coordinated rotational history. The family gained particular attention when the Galileo spacecraft flew past 243 Ida in 1993, capturing the first images of an asteroid moon, Dactyl. This encounter provided direct observational data on a Koronis family member, linking remote studies of asteroid families with in-situ exploration. The family's large membership—at least 5,949 objects—makes it a substantial population for studying the long-term dynamics and fragmentation processes in the main belt.
Did You Know?
- The Koronis family is also called the Lacrimosa family.
- Its largest known member, 208 Lacrimosa, is about 41 km in diameter.
- The Galileo spacecraft visited member 243 Ida on August 28, 1993.
More in Notable Asteroids, Part 4 1-24
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