[10] Approximately 1.00 ± 0.17 billion years old, the cluster probably contained some 6000 stars at birth,[4] but gravitational interactions and stellar evolution have since reduced the number substantially.

A recent study reported 377 confirmed member stars, with spectral types ranging from mid-F to early K, and surface temperatures relatively similar to the Sun's.

[6] The stars do, however, have an unusual (if not concentrated) distribution, with an apparent stellar corona surrounding the core, leaving the impression of a hole.

[12] The cluster has been the subject of study by the Kepler mission, with the aim of characterizing its stars' rotation rate, age, and distance to help the hunt for exoplanets.

[10] It has been described by amateur astronomers as a "smoke ring of stars" or "a jeweled mask a woman might wear at a masquerade ball".