One of the darkest bodies in the Solar System

What a 2.9% albedo means and how infrared data measured it.

Published 2026-10-23

Kalyke reflects only about 2.9% of the sunlight that falls on it.^[1]

Heat reveals size

From visible light alone, a small bright object and a large dark one can look the same. Infrared measures the heat an object gives off, which depends on its true size. Combining both breaks the tie.

WISE’s result

Infrared thermal measurements by WISE gave Kalyke an albedo of 2.9% and a diameter of about 6.9 km.^[1]

Why other sizes differ

Many small-moon sizes are estimated by assuming an albedo. NASA, for example, lists a mean radius of about 2.6 km for Kalyke.^[2] A darker real albedo means a bigger object for the same brightness.

Second largest in its group

Kalyke is the second-largest member of the Carme group, after Carme itself, about 46 km across.^[1][4]

Numbered citations link to the sources list on the Kalyke overview page.