Why Herculina has been called a toaster

A short history of models of Herculina’s shape, from speckle interferometry to the 2002 “battered cuboid”.

Published 2026-10-23

Herculina is large and fairly bright, so you might expect its shape to have been settled long ago. Instead, it took decades of disagreement.^[2]

The problem: a complicated light curve

As an asteroid spins, its brightness rises and falls. Herculina’s light curves are unusually complex, making shape and rotation hard to untangle.^[2] JPL gives its rotation period as about 9.4 hours.^[1]

Competing models

• 1982: speckle interferometry suggested a three-axis body about 260 × 220 × 215 km.^[2]
• 1985: a reanalysis proposed a non-spherical shape with one bright spot.^[2]
• 1987: a photometric study concluded it was spherical with two dark spots — and rotated around a completely different pole.^[2]
• 1988: a thermal study showed it could not be spherical.^[2]

By the late 1980s the consensus was a three-axis body with major albedo or topographic features.^[2]

The toaster

A 2002 analysis of photometric data found a blocky shape “not unlike a battered cuboid”, which it said “resembles a toaster”. It suggested several large craters, like those on 253 Mathilde, and no major brightness variation across the surface. The axis ratios came out around 1 : 1.1 : 1.3.^[2]

Herculina has never been visited by a spacecraft, so the toaster remains a model rather than a photograph.

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