From a dolphin sketch to Unicode: Thetis’s symbol

Why early asteroids had symbols, why they were dropped — and how Thetis’s returned in Unicode 17.0.

Published 2026-10-23

Before asteroids were numbered, each new one got a symbol, like the planets. Thetis’s was a dolphin and a star.^[2]

Why a dolphin?

Thetis was a sea nymph in Greek mythology, the mother of Achilles.^[2] A dolphin made a natural emblem for a sea goddess, and the star marked it as a celestial object.

Too many to draw

Thetis was the 17th asteroid found, in 1852.^[2] As discoveries multiplied, new pictograms became impractical, and astronomers switched to numbers in circles and then to the numbered designations we use today.

A digital comeback

Historic symbols are still useful for scholars reading old journals. Thetis’s symbol has now been encoded in Unicode 17.0 as U+1CECA, so it can be typed and displayed digitally where fonts support it.^[2]

Other traces in history

Thetis has also been watched passing in front of stars: one occultation was seen from Oregon in 1999, though the event was not timed.^[2]

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