Padua family
A mid-sized asteroid family with most members in z1 libration.
The Padua family (FIN: 507), also called the Lydia family, is a medium-sized asteroid family with over a thousand members. It is at least 25 million years old. Its asteroids were once linked to 110 Lydia, and most are X-type with an albedo near 0.1. Along with the Agnia family, it is the only other family where more than 75% of its members are in a z1 librating state, a nonlinear secular resonance configuration.
The family’s asteroids lie in the outer central belt, with a semi-major axis around 2.75 AU. The family is named after 363 Padua, while 110 Lydia—despite sharing the same spectral type—is now considered a possible interloper. Another former member, 308 Polyxo, was once thought to be the largest; this T-type asteroid is now classified as a background object on AstDyS.
Prominent members with known spectral types are listed, and a full catalog of Paduan asteroids is available through the Small Bodies Data Ferret.
- Fin designation
- 507
- Alternate name
- Lydia family
- Number of members
- more than a thousand
- Age
- at least 25 million years
- Predominant spectral type
- X-type
- Typical albedo
- approximately 0.1
- Typical semi-major axis
- approximately 2.75 AU
Lore & Background
The family was originally named after 110 Lydia, an X-type asteroid (M-type in the Tholen classification), which was considered its namesake. However, later work has suspected that 110 Lydia may be an interloper in the family despite having the same spectral type. The family is now named after 363 Padua, which serves as its namesake. Another asteroid, 308 Polyxo, was formerly regarded as the family's largest member, but it is no longer considered a family member and is categorized as a background asteroid. The Padua family is located in the outer part of the central asteroid belt, with a semi-major axis of approximately 2.75 AU. Its members are predominantly X-type asteroids with an albedo of about 0.1. The family is at least 25 million years old.
Reader's Guide
The Padua family holds significance as one of only two known asteroid families where the majority of members are locked in a nonlinear secular resonance, specifically the z1 librating state, which affects their orbital evolution. This dynamical configuration provides insights into the long-term gravitational interactions within the asteroid belt. The family's age of at least 25 million years places its formation in a relatively recent epoch compared to many other families. The uncertainty surrounding the status of 110 Lydia—whether it is a true member or an interloper—highlights the challenges in asteroid family classification, where spectral similarity does not guarantee common origin. The reclassification of 308 Polyxo as a background asteroid further illustrates the ongoing refinement of family membership. The family's large size, with over a thousand members, makes it a significant population for studying collisional processes and orbital dynamics in the outer central belt.
Did You Know?
- The Padua family is also known as the Lydia family.
- 308 Polyxo was formerly considered the family's largest member but is now classified as a background asteroid.
More in Notable Asteroids, Part 4 1-24
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