What happened to 3I/Atlas? Interstellar comet reappears without a tail after passing behind the Sun

After several weeks of not being seen, comet 3I/Atlas is visible again in the sky. But when scientists looked at it, they noticed something different — the comet no longer has its bright glowing tail.

The comet had disappeared behind the Sun for a few weeks, and many thought it might not survive the heat. Now that it has come back, its changed look has caught everyone’s attention and raised new questions about what happened while it was near the Sun.

A visitor from outside our Solar System

3I/Atlas is not a normal comet. It came from outside our Solar System, making it a rare interstellar visitor. It is only the third such object ever found — after ‘Oumuamua in 2017 and 2I/Borisov in 2019.

When scientists first discovered 3I/Atlas earlier this year, they noticed it was moving too fast to be from our own Solar System. Its path showed that it was passing through from another star system and would eventually continue traveling back into deep space.

It disappeared behind the Sun

In late October, 3I/Atlas moved behind the Sun — a point called perihelion, which means its closest approach to the Sun. During that time, the Sun’s bright light made it impossible for telescopes on Earth to see it.

Because of the strong heat and radiation, scientists weren’t sure if the comet would survive. Many comets break apart when they get too close to the Sun.

Now it’s back — but looks different

When the comet became visible again, scientists noticed that its tail was missing. Normally, a comet’s tail is made when the Sun’s heat melts ice and dust from its surface, creating a glowing trail behind it.

Experts believe that 3I/Atlas lost its tail because of the Sun’s heat. The ice and gas that made up its tail may have burned away during its close pass. Another reason could be that the solar wind — strong particles flowing from the Sun — blew the tail away.

Some scientists also said the tail might still exist but is facing away from Earth, making it hard for us to see from our angle.

Scientists dismiss alien theories

When 3I/Atlas got close to the Sun, ultraviolet (UV) rays began to break down large hydrocarbon molecules — compounds made of carbon and hydrogen — in the comet’s atmosphere. This process creates a gas called diatomic carbon (C₂), which gives many comets their faint greenish glow.

One scientist explained it simply.

“It’s similar to how our skin gets sunburned by UV rays,” said Zhang. “The UV light breaks apart molecular bonds — in this case, within the comet’s gases.”

This reaction shows how sunlight can change a comet’s color, brightness, and even shape as it travels through space.

Scientists continue to study it

Now that 3I/Atlas can be seen again, researchers are studying it carefully using telescopes both on Earth and in space.

They want to learn more about what it’s made of and how it survived the Sun’s heat. Since this comet came from another star system, it could help scientists understand how planets and stars form in other parts of the galaxy.

Even though it no longer has a tail, 3I/Atlas remains an important discovery. Its return gives scientists another chance to learn about objects that travel through our Solar System from distant stars.

For now, astronomers will keep watching 3I/Atlas as it slowly moves away from the Sun and continues its long journey through space.

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