Mercer 3, also known as GLIMPSE-C02, is a heavily obscured globular cluster embedded in the disk of the Milky Way galaxy.

[1] It was discovered in 2008 in the data obtained by 2MASS and GLIMPSE infrared surveys, and independently characterized by two groups.

It had avoided detection for such a long time due to the extremely strong foreground extinction in its direction reaching 24 magnitudes in the visible light.

Mercer 3 is probably situated at the distance from 4 to 8 kpc from the Sun and has a half-light radius of 0.7–1.5 pc.

[1] Mercer 3 is an old globular cluster having the age of about 12 billion years.