3I/ATLAS interstellar comet glows green in new image, astronomer links it to sunscreen

Astronomer Qicheng Zhang reportedly captured new images of comet 3I/ATLAS since it slipped behind the Sun on October 29. The images reveal that the interstellar visitor "is glowing green and hiding its tail."

According to a Live Science report, Qicheng Zhang, a researcher at the Lowell Observatory in Arizona, used the observatory's powerful Discovery Telescope to make fresh observations of the interstellar comet as it zoomed away from the sun on Wednesday (November 5).

The comet recently became visible again after swinging around the far side of our star.

The green glow

As per the report, the researcher used a filter to detect diatomic carbon (C2) particles, which glow green.

He noted that there's a bunch of large molecules in the comet that contain carbon and hydrogen (hydrocarbons).

And when the comet gets close to the sun, ultraviolet (UV) light breaks these molecules apart.

"It's sort of for the same reason that if we stay out in the sun too long without sunscreen, we get sunburnt," Zhang told Live Science.

"The UV rays are destroying our DNA [in our skin cells], which is kind of a similar type of molecule in the sense that it's big and contains carbon."

When this happens on a comet, some of the molecule chunks are two carbon atoms stuck together, or diatomic carbon, which are easy for astronomers to detect.

Earlier, it was reported that the comet had “changed colour” upon getting close to the Sun. It turned a bright blue instead of the usual red.

3I/ATLAS was bluer before: What does new green colour mean?

On October 28, Zhang and his colleague released a study to the preprint server arXiv that suggested comet 3I/ATLAS underwent rapid brightening ahead of perihelion [when getting close to Sun] and was distinctly bluer than the sun.

The green in the new image doesn't mean that the comet changed colour after perihelion — it might have changed colour before, the report added.

Zhang said that, in astronomical terms, bluer or redder typically refers to longer (red) or shorter (blue) wavelengths of light, with the new observation matching the latter.

The comet is a lot brighter when viewed with bluer filters than redder filters, though the bluer filters are more of a mix of green and blue, and not actually that sensitive to pure blue.

3I/ATLAS's hidden tail

The comet appears to lack a dust tail in the image, but it's still there, Live Science reported.

Zhang told the media outlet that if we look closely at the image, one can see it's a bit brighter on the left side of the comet than on the right.

That slight asymmetric glow occurs because we're seeing the tail basically head-on, and it's right behind the comet, curving slightly off to the left.

In other words, the comet's apparent lack of tail isn't anything to get excited about.

What we know about Comet 3I/ATLAS

Comet 3I/ATLAS has only recently become visible from Earth again after it briefly disappeared behind the sun, reaching its closest point to our star, known as perihelion, on Oct. 29.

This post-perihelion phase opens up a critical window for astronomers hoping to learn more about the comet's gases and makeup, as comets tend to be their most active at perihelion.

This comet, which NASA says came from outside our solar system, was discovered in July this year. The comet is only the third interstellar visitor ever recorded and could be the oldest comet ever seen, with one study suggesting it's around 3 billion years older than the solar system.