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Interstellar comet 3I/ATLAS brightened rapidly as it zoomed behind the Sun, a new study has revealed. This rare object is flying around the Sun to reach perihelion (closest point to the Sun) on Thursday (October 30).
Comet 3I/ATLAS is a newly identified interstellar object, meaning it comes from outside our Solar System. It is only the third of its kind seen so far, following 1I/Oumuamua in 2017 and 2I/Borisov in 2019. It was discovered on July 1, 2025.
It could not be seen from Earth. However, the European Space Agency (ESA) said its astronomers have begun using ground-based telescopes in Hawaii, Chile and Australia to monitor 3I/ATLAS’s progress.
So far, the comet has been observed by near-Earth space telescopes, including the NASA/ESA Hubble Space Telescope and the NASA/ESA/CSA James Webb Space Telescope.
Additionally, according to Universe Today, some of the satellites tracking it include the National Oceanic and Atmospheric Administration’s GOES-19 weather satellite, NASA’s Polarimeter to Unify the Corona Heliosphere (PUNCH) mission, as well as NASA and ESA’s Solar and Heliospheric Observatory (SOHO).
Despite some wild speculation that comet 3I/ATLAS might be an alien spacecraft, most astronomers are confident that this interstellar visitor is a space rock from an unknown star system far away.
‘shining brightly’
On Wednesday (Oct. 28), two researchers posted a study on the preprint server arXiv reporting that comet 3I/ATLAS was rapidly brightening before perihelion.
The team estimates that, at perihelion, the comet will have brightened to about magnitude 9 – still too dim to see with the unaided eye, but bright enough to be seen by good backyard telescopes if visible from Earth.
The study relied on space-based solar instruments such as GOES-19 and SOHO, and found that the comet was “distinctly bluer than the Sun”, which, according to the study authors, was consistent with gas emissions significantly contributing to the comet’s increased brightness near perihelion.
This is expected from comets, which heat up as they approach the Sun, causing surface ice to convert into gases that wrap around the comet’s body and contribute to its tail.
Solar radiation ionizes the gas, creating even more brightness.
What is unusual about Comet 3I/ATLAS?
According to Live Science, the findings so far indicate that Comet 3I/ATLAS is hurtling through our solar system at more than 130,000 mph (210,000 km/h) in an unusually flat and straight trajectory.
Meanwhile, NASA previously said that 3I/ATLAS is traveling through our solar system at “the highest velocity ever recorded for a solar system visitor.”
NASA said, “This breathtaking run is evidence that the comet has been drifting in interstellar space for many billions of years… The longer 3I/ATLAS remained in space, the greater its speed increased.”
In fact, 3I/ATLAS may be the oldest comet ever seen, experts have said. One study even suggests that it is about 3 billion years older than our 4.6 billion year old solar system.
The comet is also possibly the largest interstellar object ever observed, although researchers are still determining its exact size. Hubble Space Telescope data show that 3I/ATLAS has a maximum width of about 3.5 miles (5.6 km).
When will the comet be visible to Earth-based telescopes?
By the time the comet reaches its closest point to Earth, it will be hidden behind the Sun. It is scheduled to reappear in late November, giving astronomers another chance to study it. During its closest approach to Earth, it will be on the other side of the Sun, ESA said.
According to NASA, the comet will become visible again to Earth-based telescopes in early December, and may also be visible to spacecraft orbiting Jupiter as it approaches the gas giant in March, 2026.
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