Why is Iphigenia so dark?

An albedo of 0.042, a carbonaceous classification, and what dark asteroids tell us about the early Solar System.

Published 2026-10-23

Iphigenia reflects only about 4% of the sunlight that falls on it, according to JPL’s geometric albedo of 0.042.^[1]

What albedo means

Albedo measures how reflective a surface is. Bright, icy or stony surfaces reflect more; carbon-rich material absorbs most light. Iphigenia’s value puts it among the darkest asteroids.^[1]

A carbonaceous body

Iphigenia is classified as a C-type asteroid, which means it probably has a primitive carbonaceous composition.^[2] JPL’s database lists it as DCX in the Tholen scheme and Ch in the SMASS scheme.^[1]

Why “primitive” matters

Primitive asteroids have changed relatively little since the Solar System formed. Studying them is like reading the raw ingredients from which the planets were built.

Dark and slow

Iphigenia also rotates slowly — about 31.4 hours per turn — with its brightness changing by 0.30 magnitude each rotation.^[2] Because it is so dark, it appears faint for its 70 km size, which makes careful photometry like this harder.^[1][4]

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