KEY DEVELOPMENTS

• Interstellar object 3I/ATLAS rapidly brightened as it swung behind the sun toward perihelion on October 29, with spacecraft observations revealing the comet's dramatic increase in luminosity.
• Amateur astronomer Worachate Boonplod spotted the comet in images from NOAA's GOES-19 weather satellite on October 18, noting that 3I/ATLAS was easily detectable with brightness comparable to nearby stars at magnitude 11.
• Multiple NASA and European Space Agency spacecraft including the Polarimeter to Unify the Corona Heliosphere (PUNCH) mission and the Solar and Heliospheric Observatory (SOHO) tracked the object until October 26.

NASA has been studying the icy visitor with space telescopes including Hubble, Webb, and SPHEREx, and the object is on course to venture past Jupiter in March 2026 on its way out of our solar system.

Two researchers posted a study on October 28 to the preprint server arXiv reporting that 3I/ATLAS underwent rapid brightening ahead of perihelion, estimating the comet brightened to roughly magnitude 9 at closest approach—still too faint for the naked eye but bright enough for good backyard telescopes if it were visible from Earth.

3I/ATLAS is recognized as an interstellar object because of its extremely hyperbolic path and very high-speed relative to the Solar System, with an orbital eccentricity of 6.137—making the trajectory appear relatively straight rather than curved. Scientists indicate the comet is zooming through our solar system at speeds in excess of 130,000 mph in an unusually flat trajectory.

The speed of the comet, which has the highest velocity ever recorded for a solar system object, suggests it has been traveling for billions of years, gaining momentum from a gravitational slingshot effect as it whips by stars.

The study examining GOES-19 and SOHO data found the comet was distinctly bluer than the sun. Researchers suggest the rapid brightening may result from the cooling effect of sublimating carbon dioxide ice holding water-ice vaporization in check as the object approached the Sun.

The 3I/ATLAS is only the third interstellar object ever recorded, following 1I/'Oumuamua in 2017 and 2I/Borisov in 2019. The NASA-funded ATLAS survey telescope in Rio Hurtado, Chile, first reported observations to the Minor Planet Center on July 1, 2025. NASA has categorized this object as interstellar because of the hyperbolic shape of its orbital path—it does not follow a closed orbital path about the Sun.

One study suggests 3I/ATLAS is around 3 billion years older than our 4.6 billion-year-old solar system. The object is also likely the largest interstellar object ever seen, with Hubble Space Telescope data suggesting 3I/ATLAS has a maximum width of about 3.5 miles.

Comet 3I/ATLAS poses no threat to Earth and will remain far away, with its closest approach to our planet at about 1.8 astronomical units (approximately 170 million miles) on December 19, 2025. The comet reached its closest point to the Sun around October 30 at a distance of about 1.4 astronomical units (130 million miles)—just inside the orbit of Mars.

From October 30 to November 6, Europa Clipper will potentially be immersed within the ion tail of 3I/ATLAS, providing the opportunity to detect the signatures of an interstellar comet's ion tail. Spacecraft Hera will possibly be immersed within the ion tail of 3I/ATLAS from October 25 to November 1.

WHAT'S NEXT

The object will become visible again to Earth-based telescopes by early December, and may even be visible to spacecraft orbiting Jupiter as it makes a close approach to the gas giant in March 2026. Throughout its run, 3I/ATLAS is expected to fade from around 11th magnitude in mid-November to 12.5 by the 30th, then another 2 magnitudes by the end of December. The object will remain observable through December 2025 as it moves through the constellations Virgo and Leo before continuing its journey out of the solar system.