NASA’s PUNCH Captures Unprecedented 40-Day Timelapse of Comet SWAN — Brief Glimpse of Interstellar 3I/ATLAS

NASA's PUNCH Watches Comet C/2025 R2 (SWAN) for Nearly 40 Days

One of NASA's newest heliophysics spacecraft delivered a rare, near-continuous view of a comet as it moved through the inner solar system. From Aug. 25 to Oct. 2, the PUNCH mission imaged Comet C/2025 R2 (SWAN) roughly every four minutes — producing what NASA calls perhaps the longest high-cadence tracking of a comet to date.

The timelapse stitches together hundreds of frames showing SWAN gliding across the sky between bright Mars and the star Spica in Virgo. Because the frames were combined before full processing, thin dark seams marking the boundaries between individual exposures remain visible in the composite video.

Discovery and Orbit

The comet was first identified in September by Ukrainian amateur astronomer Vladimir Bezugly, who spotted a bright blob near the Sun while reviewing publicly available images from the Solar and Heliospheric Observatory (SOHO). Just one day after discovery SWAN reached perihelion — its closest approach to the Sun — passing about 46.74 million miles (75.20 million km) from our star.

Appearance and Behavior

Early PUNCH images revealed a bluish-green coma produced as sunlight sublimated ices from the comet’s nucleus. Gas and dust released in that process were swept back by the solar wind, forming the glowing tail visible in many frames. By mid-September the coma developed an unusual triangular, "hammerhead" profile — a distortion often linked to fragmentation of the nucleus, where outgassing from multiple pieces produces an asymmetric, stretched coma.

Interstellar Visitor and Solar Wind Tracing

During PUNCH’s observing window SWAN shared the same patch of sky with interstellar object 3I/ATLAS. The timelapse briefly shows 3I/ATLAS near the end of the sequence as a fast-moving point beneath SWAN. Comet tails act as natural tracers of the solar wind — the continuous stream of charged particles flowing outward from the Sun — so observations like these help researchers map space weather effects across the solar system.

“Other comets have been tracked at once-per-day cadence for years,” said Craig DeForest, PUNCH principal investigator at the Southwest Research Institute. “What's new here is the few-minute cadence of observation.”

“Watching the Sun's effects from multiple vantage points — and with different types of instruments — is what gives us a complete picture of the space environment,” added Gina DiBraccio, acting director of the Solar System Exploration Division at NASA's Goddard Space Flight Center. She noted these measurements help protect astronauts, spacecraft, and Earth-based technology from space weather.

Close Approach to Earth

In late October SWAN made its closest approach to Earth at about 25.10 million miles (40.38 million km), placing it near naked-eye visibility and easily within reach of binoculars and small telescopes for dedicated observers.