Interloper 3I\/ATLAS makes a color shift as it leaves the sun.<\/p>\n\n\n\n
In the spirit of the season, the interstellar comet 3I\/ATLAS<\/u><\/a> is changing color as it leaves the sun<\/u><\/a> behind \u2014 shifting from a reddish tint to a faint green glow. <\/p>\n\n\n\n That visible change signals the comet<\/u><\/a> is reacting to solar heat and releasing new gases in space<\/u><\/a>, giving scientists fresh clues about what it is made of and how it behaves.<\/p>\n\n\n\n Astronomers used the Gemini North telescope in Hawaii to capture new color images of the comet after it emerged from the other side of the sun on Nov. 26. Earlier images taken from Gemini South in Chile showed the comet looking redder. That ruddy color comes from gases surrounding the comet \u2014 called a coma \u2014 that heat up and shine as frozen material turns directly into gas, skipping the liquid phase. Some of those gases emit green light, which Gemini\u2019s cameras can detect.<\/p>\n\n\n\n “Interstellar comet 3I\/ATLAS has a post-perihelion greenish glow in time for the holidays,” said Bryce Bolin, a research scientist from Eureka Scientific who led the observations, in a post on X<\/a>.\u00a0<\/p>\n\n\n\n Just days later, a space telescope added another piece to the puzzle. The European Space Agency\u2019s XMM-Newton spacecraft observed 3I\/ATLAS<\/a> in X-rays for nearly 20 hours on Dec. 3. X-rays are a very high-energy form of light that human eyes cannot see.<\/p>\n\n\n\n The new observations offer a rare chance to study material from another star system while the comet is still somewhat close. By tracking its changes across multiple types of light, scientists can better identify what it’s made of and consider how interstellar objects form. <\/p>\n\n\n\n Comet 3I\/ATLAS came from another part of the galaxy<\/u><\/a> and was later ejected \u2014 likely by a gravitational jolt from a planet or passing star \u2014 before drifting across interstellar space for hundreds of millions of years. Only two other confirmed interstellar visitors have ever been sighted: ‘Oumuamua<\/u><\/a> in 201, which wasn’t a comet, and Comet 2I\/Borisov<\/u><\/a> in 2019.<\/p>\n\n\n\n The latest visitor entered the solar system traveling roughly 137,000 mph, a speed far too fast for the sun\u2019s gravity to trap it. Scientists say that means it’s only swinging by and will never return.<\/p>\n\n\n\n Comets are icy boulders that heat up<\/u><\/a> as they approach the sun, releasing gas and dust in bright, sweeping tails<\/u><\/a>. Most known comets are leftover materials from the solar system\u2019s construction 4.6 billion years ago, though thousands more likely lurk beyond Neptune in the Kuiper Belt<\/u><\/a> and, farther still, in the Oort Cloud<\/u><\/a>.<\/p>\n\n\n\n NASA<\/u><\/a> and ESA have pointed many spacecraft cameras at the comet \u2014 including the Hubble and James Webb Space Telescope<\/u><\/a>, the Mars Reconnaissance Orbiter, and the Lucy and Psyche missions \u2014 to collect as much information as possible while the space interloper remains in the solar system.<\/p>\n\n\n\n The Gemini North pictures took place during a live public event organized through Shadow the Scientists<\/u><\/a>. The program invites students and the public into telescope control rooms so they can watch astronomers work in real time. As the telescope tracked the comet, it stayed sharp in the images while background stars streaked across the frame in different colors.<\/p>\n\n\n\n Scientists are especially interested in how 3I\/ATLAS will continue to change. Comets often respond slowly to the sun’s heat, because warmth takes time to reach their interiors. As a result, new gases can begin escaping later, or the comet may suddenly brighten.<\/p>\n\n\n\n