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Today in History: William Lassell discovers Uranian moons Umbriel and Ariel

10/24/2025

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Summary

Story summary

On October 24, 1851, English astronomer William Lassell discovered Umbriel and Ariel, the third and fourth moons of Uranus. Umbriel, primarily composed of ice and rock, features a dark surface shaped by impacts and evidence of early geological activity. These discoveries expanded our understanding of Uranus's complex moon system.

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Story summary

On October 24, 1851, English astronomer William Lassell discovered Umbriel and Ariel, the third and fourth moons of Uranus. Umbriel, primarily composed of ice and rock, features a dark surface shaped by impacts and evidence of early geological activity. These discoveries expanded our understanding of Uranus's complex moon system.