Halimede.space

Will Halimede hit Nereid?

A 41% chance over 4.5 billion years.

Published 2026-10-23

Nereid is Neptune’s third-largest moon, known for its very eccentric orbit.[4]

Crossing paths

At maximum eccentricity, Halimede can come within 1.66 million km of Neptune, crossing Nereid’s orbit.[1]

The odds

A 2004 study led by Holman estimated a 41% chance of impact over 4.5 billion years.[1]

Rare encounters

Close approaches are rare: the two don’t come within 180,000 km of each other over 30,000 years.[1]

A fragment?

Halimede’s similar colour led to the idea it might be a piece of Nereid — though it could instead be one of Neptune’s original captured irregular moons.[1]

Numbered citations link to the sources list on the Halimede overview page.

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