Odysseus (crater)

Lore & Background

Odysseus was discovered by the Voyager 2 spacecraft on 1 September 1981 during its flyby of Saturn. The crater is quite flat for its size of approximately 450 km; its floor conforms to Tethys's spherical shape, likely due to viscous relaxation of the icy crust over geologic time. The floor lies about 3 km below the mean radius, while the exterior rim is about 5 km above the mean radius, giving a relief of 6–9 km. Inside the crater, the rim is composed of arcuate scarps extending about 100 km until the floor is reached. Several graben, 10–20 km wide and hundreds of kilometers long, radiate away from Odysseus, likely cracks from the impact; the most prominent is Ogygia Chasma. The crater originally had a deep bowl, high mountainous rim, and towering central peak, but over time the floor relaxed to Tethys's spherical shape and the rim and central peak collapsed, indicating Tethys was warm and malleable at the time of impact—possibly with a liquid interior. If Tethys had been colder and more brittle, the moon might have shattered or retained the crater's shape, like Herschel on Mimas. The central complex, Scheria Montes, features a central pit-like depression 2–4 km deep, surrounded by massifs elevated 2–3 km above the crater floor.

Reader's Guide

Odysseus is significant as one of the largest craters in the Solar System, dominating the surface of Tethys. Its flat, relaxed shape provides key evidence about the thermal history of Tethys: the crater's collapse implies that at the time of impact, the moon's icy crust was warm and malleable, possibly even liquid, allowing viscous relaxation over geologic time. This contrasts with the crater Herschel on Mimas, which retained its shape due to a colder, more brittle crust. The radiating graben, including Ogygia Chasma, are likely impact-induced cracks. The relationship between Odysseus and the immense trench Ithaca Chasma was hypothesized but later disputed: high-resolution Cassini images showed that crater counts inside Odysseus are lower than in Ithaca Chasma, indicating Ithaca Chasma is older and not formed by the Odysseus impact. Thus, Odysseus serves as a marker for dating surface features and understanding the internal state of Tethys during the early Solar System.

Did You Know?

• Odysseus is 445 km across, more than 2/5 of Tethys's diameter.
• The crater's floor conforms to Tethys's spherical shape due to viscous relaxation.
• Odysseus was discovered by Voyager 2 on 1 September 1981.
• The central complex Scheria Montes contains a pit-like depression 2–4 km deep.