Universe Guide

Why does Earth not have rings?

All the gas giants in the Solar System have rings and even a few asteroids such as Charilklo have a ring but why doesn't Earth.

It would seem that once, Earth did have rings like the gas giants billions or years ago. When the Earth was young, it was hit by an asteroid. That asteroid threw debris into the air which settled in a ring formation. Over time, the debris coalesced to form our Moon.

If a moon got too close to its planet, it would be ripped apart and the debris would become a ring system. The moon would have to get within the Roche Limit. The Roche Limit is the minimum distance an object can be before it is shredded to bits by the larger object. Roche is named after Edouard Roche, a French Astronomer from the 19th century.

The Roche Limit is 2.5 times the radius of the planet. For Earth, the roche limit is about 10,000 km of which the Moon is farther away than that. In a few billion years time, the moon might gravitate towards Earth, caused by the Sun moving out of the main sequence and growing. When the moon comes closer to the Earth, the moon will be ripped apart and the Earth will have a ring system. At the moment, the moon is moving away from the Earth at about 3 inches a year. Mental Floss

Mars's moon Phobos is gradually moving closer towards its planet and within 50 million years, the moon will be shredded. Mars will have gained a very thin moon system. Stackexchange

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