What Cassini Discovered on the Surface of Tethys Stunned Scientists | Our Solar System's Moons

Summary

Tethys, a moon of Saturn, is a remarkable survivor, shaped by extreme events. Despite its icy, seemingly unremarkable appearance, it boasts features like the vast Ithaca Kasma canyon and the giant Odysseus impact crater, both signs of its tumultuous history. Tethys' composition of nearly pure water ice and low density reveals its unique internal structure, while its interaction with Saturn's rings influences its surface. Despite having no atmosphere, Tethys remains an intriguing world, enduring impacts and internal forces, showing resilience in the harshest conditions of the solar system.

Takeaways

• 😀 Tethys, one of Saturn's moons, is an icy survivor with a history of enduring violent internal and external forces.
• 🌍 Tethys' surface features include Ithaca Kasma, an enormous canyon system, and the Odysseus impact crater, both of which tell the story of the moon's geological history.
• 🌕 Tethys was first observed by Giovanni Dominico Cassini in 1684, and its name comes from a Titaness of the sea in Greek mythology.
• ❄️ Tethys' low density (0.97 g/cm³) indicates it is composed mostly of water ice, with a small amount of rocky material, and suggests it may not have fully differentiated into a distinct core.
• 🪐 Tethys' irregular shape results from gravitational interactions with neighboring moons, leading to its tri-axial ellipsoid form.
• 🌌 Ithaca Kasma, the largest canyon system on Tethys, may have formed as the moon expanded due to the freezing of a subsurface ocean, causing the crust to crack.
• 💥 The Odysseus crater, one of the largest impact basins on Tethys, likely occurred when the moon's interior was still partially molten, helping it absorb the massive impact energy.
• 🔬 Tethys' icy surface reflects 60% of sunlight, giving it a high albedo, and its lack of a significant atmosphere exposes it to space weathering, including micrometeoroid impacts.
• 🕹️ Tethys has an intriguing thermal anomaly where its leading hemisphere is cooler during the day but warmer at night, creating a 'Pac-Man' shaped heat map.
• 💡 Tethys orbits Saturn in a tidally locked orbit, with its leading hemisphere exposed to more external weathering from Saturn's E-ring and Enceladus' plumes, making it brighter and more reflective than the trailing hemisphere.

Q & A

What is the primary composition of Tethys?

Tethys is primarily composed of water ice, with a small amount of rocky material integrated within. Its low density suggests it has a small, possibly undifferentiated core.

How did Tethys get its name?

Tethys was named after a Titaness and Sea goddess from Greek mythology, following a naming convention proposed by John Hershel in the 19th century.

What is Ithaca Kasma, and why is it significant?

Ithaca Kasma is a vast canyon system on Tethys that spans 2,000 km in length, 100 km in width, and 5 km in depth. It is one of the largest canyon systems in the solar system and provides clues about Tethys' internal evolution, potentially caused by the freezing of a subsurface ocean.

What causes the formation of Ithaca Kasma on Tethys?

Ithaca Kasma likely formed due to internal pressure caused by the freezing of a subsurface ocean. As water expanded when it froze, it stressed Tethys' icy outer crust, causing it to crack and form the canyon system.

What is the Odysseus crater, and how did it affect Tethys?

The Odysseus crater is the largest impact basin on Tethys, measuring 450 km across. The impact that created it occurred when Tethys was still partially molten or slushy, allowing the moon to absorb the impact rather than shatter.

Why is the Odysseus crater relatively shallow compared to other craters?

The Odysseus crater is shallow because of a phenomenon called viscous relaxation, where the depression and uplifted rim slowly slumped under Tethys' gravity over geological time, gradually smoothing out the crater's profile.

What is the Pac-Man heat map on Tethys?

The Pac-Man heat map on Tethys is a thermal anomaly observed by Cassini's infrared spectrometer. It shows that the lower latitudes of Tethys' leading hemisphere are cooler during the day and warmer at night compared to other regions, resembling a giant Pac-Man shape.

What factors contribute to the Pac-Man heat map on Tethys?

The Pac-Man heat map is caused by the differential weathering on Tethys' surface, driven by interactions with Saturn's E-ring particles and Saturn's magnetosphere. These external factors affect the moon's surface, leading to thermal variations.

How does Tethys' lack of atmosphere affect its surface?

Tethys' lack of atmosphere leaves its surface exposed to harsh space conditions, including micrometeoroid impacts, solar radiation, and charged particles from Saturn's magnetosphere, contributing to the moon's icy, weathered appearance.

What role do Saturn's rings play in shaping Tethys?

Saturn's rings influence Tethys by bombarding its leading hemisphere with icy particles from the E-ring and by affecting its surface with energetic plasma from Saturn's magnetosphere. These interactions result in variations in surface brightness and temperature.