Tethys

The Giant Bullseye Moon

An extremely bright, icy moon with a massive impact crater creating a giant bullseye pattern

Orbital Period

1.89 days

Tidal Locking

Yes

Same face always visible

Planet Rotations

4.2×

per orbit

Atmosphere

🌙 Mind-Blowing Fact

Tethys has one of the largest craters in the solar system relative to the moon's size - Odysseus crater is 400km across on a 1,060km moon! It's like a giant bullseye covering 40% of one hemisphere!

What is Time on Tethys?

Tethys is one of Saturn's brightest moons - almost pure water ice that reflects sunlight brilliantly. It's famous for its giant Odysseus crater and the mysterious Ithaca Chasma.

The 1.9-Day Orbit

One orbit = 1.89 Earth days - Fast pace!
Extremely bright - Second brightest Saturnian moon
Saturn fills 14° of sky - Spectacular view!
Quick sunrises - Day/night cycle in under 2 Earth days

Odysseus Crater: The Giant Impact

Tethys's defining feature is Odysseus crater:

400 km across (2/5 of Tethys's diameter!)
Likely from an impact billions of years ago
Should have shattered Tethys completely
Survived because Tethys was still partially molten
Crater floor has rebounded - not as deep as expected

Ithaca Chasma: The Great Canyon

A massive canyon system extends across Tethys:

100 km wide
3-5 km deep
2,000 km long (3/4 of Tethys's circumference!)
Possibly related to Odysseus impact
Or from internal expansion/freezing

The Bright Ice World

Tethys is extremely bright (albedo 0.8-0.9):

Almost pure water ice surface
Very little dark material
Reflects 80-90% of sunlight
One of the brightest objects in solar system

A Day in the Life

Inside the Bullseye

You stand in the center of Odysseus crater, the massive impact basin that dominates Tethys. The crater walls curve away in all directions, 200 kilometers in every direction.

"This crater is 40% of Tethys's diameter," your guide says. "If a proportional crater hit Earth's Moon, it would be 1,400 kilometers across - larger than Texas."

You look up at the crater rim, barely visible on the horizon. Somewhere beyond that rim is Ithaca Chasma, the great canyon that may have formed from this very impact.

"The impact should have destroyed Tethys completely," the guide continues. "But Tethys was still partially molten when it happened. The moon absorbed the impact, the crater floor rebounded, and Tethys survived."

Saturn rotates overhead, visible through the bright sky. In 1.89 days, Tethys will complete its orbit. Saturn will rotate 4.2 times. And Odysseus crater will still be here, a 4-billion-year-old reminder that time can survive even the most catastrophic impacts.

"How long did it take for the crater to form?" someone asks.

"Minutes," the guide says. "The impact, the crater formation, the shock wave - all minutes. But the crater has been here for billions of years. Time works differently for impacts and orbits."

Thought Experiments

Why didn't the Odysseus impact destroy Tethys?

The impact occurred when Tethys was still partially molten, early in its history. A molten or partially molten body can absorb impact energy more effectively than a solid body. The impact created the crater, but the warm interior allowed the crater floor to rebound and the moon to hold together. If the same impact happened today, it would likely shatter Tethys completely.

Is Ithaca Chasma related to Odysseus crater?

Possibly! One theory is that the Odysseus impact sent shockwaves through Tethys, creating fractures on the opposite side that became Ithaca Chasma. Another theory is that Tethys expanded as its interior froze (ice expands), cracking the surface. Both theories are debated - we need more data to know for sure.