The interstellar invader Comet 3I/ATLAS is continuing to surprise scientists, this time by brightening at an unexpectedly rapid pace as it made its closest approach to the sun. Experts studying the object don't yet know why that happened.

3I/ATLAS is only the third object known to have entered our solar system from another planetary system — after the cigar-shaped space-rock 'Oumuamua, discovered passing through the solar system in Oct. 2017, and the first interstellar comet 2I/Borisov, spotted in our stellar backyard in August 2019. The brief presence of these bodies in the solar system offers a unique glimpse into the chemical makeup around other stars.

Scientists had expected 3I/ATLAS to brighten as it made its closest approach to the sun, or reached perihelion, on Wednesday (Oct. 29)

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