The faintest moon Cassini measured

What a nearly flat light curve tells us about Fornjot.

Published 2026-10-23

Fornjot was the faintest moon measured by Cassini–Huygens.^[1]

Flat brightness

Elongated moons brighten and dim as they rotate. Fornjot shows very little variation, so it is probably very round.^[1]

An uncertain day

Because the variation is so small, its rotation period is ambiguous: 6.9 or 9.5 ± 0.4 hours.^[1]

Size

It is about 6 km across.^[1] NASA estimates a radius of 3 km assuming an albedo of 0.04.^[2]

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