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Birthday · September 26, 2025

A SWAN, an ATLAS, and Mars

September 26, 2025

The cosmos has been expanding since the beginning of time, making room for galaxies, for stars, for planets — and ultimately, for you.

A SWAN, an ATLAS, and Mars

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APOD published September 26, 2025. Credit: Adam Block. A publication-date match, not a photo taken on your date. Independent of NASA.

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A SWAN, an ATLAS, and Mars

Original APOD · September 26, 2025

A new visitor to the inner Solar System, comet C/2025 R2 (SWAN) sports a long ion tail extending diagonally across this almost 7 degree wide telescopic field of view recorded on September 21. A fainter fellow comet also making its inner Solar System debut, C/2025 K1 (ATLAS), can be spotted above and left of SWAN's greenish coma, just visible against the background sea of stars in the constellation Virgo. Both new comets were only discovered in 2025 and are joined in this celestial frame by ruddy planet Mars (bottom), a more familiar wanderer in planet Earth's night skies. The comets may appear to be in a race, nearly neck and neck in their voyage through the inner Solar System and around the Sun. But this comet SWAN has already reached its perihelion or closest approach to the Sun on September 12 and is now outbound along its orbit. This comet ATLAS is still inbound though, and will make its perihelion passage on October 8.

Image credit: Adam Block

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