While Comet Lemmon is lighting up Earth’s night sky, another traveler from deep space is quietly preparing for its big moment behind the sun. The interstellar comet 3I/ATLAS, an icy visitor from another star system, is about to reach its most dramatic stage as it races toward the sun at incredible speed.
Confirmed by NASA, 3I/ATLAS is only the third interstellar object ever spotted in our solar system, following Oumuamua and 2I/Borisov. It is also the largest and fastest, measuring up to 11 kilometers wide and moving at roughly 70,000 miles per hour. Astronomers think it could be billions of years old, formed long before the birth of our own sun.
On Wednesday, October 29, the comet will reach perihelion, its closest point to the sun, coming within about 130 million miles or 210 million kilometers. That is when the real show begins. As sunlight heats its icy surface, the comet will start venting gas and dust in powerful jets that create a glowing cloud called a coma. Solar wind will then stretch that material into a bright tail, pointing away from the sun as 3I/ATLAS accelerates through space.
A new image from the Gemini South telescope in Chile shows the comet cutting across the stars, leaving a long, hazy plume behind. The picture combines dozens of short exposures, revealing the nucleus surrounded by a faint, developing tail. This may be the clearest view yet of an object that came from another solar system.
As 3I/ATLAS nears the sun, scientists expect it to become much more active. It could brighten significantly as it releases more gas and dust, making it easier for telescopes to track when it reappears from behind the sun in early November. Some researchers believe the heat could even cause it to fragment, which would make it briefly brighter but far less stable.
Studying this comet gives astronomers a rare chance to analyze material that formed around a different star. Its structure and chemistry could help explain how comets develop in other planetary systems and what happens when they encounter extreme solar radiation for the first time.
Once 3I/ATLAS passes its closest point, it will begin its long journey out of the solar system and back into interstellar space. But before it goes, this alien visitor may deliver a final burst of activity, giving Earth’s astronomers one last chance to watch it flare up in spectacular fashion.