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Comet C/2024 G3 (ATLAS) wagging its tail

“Comets are like cats: they have tails, and they do precisely what they want,” wrote David H. Levy, an amateur astronomer who discovered 23 comets. These cosmic visitors can indeed be pretty capricious. We never know exactly how long a comet will be visible in the sky.

In January, the southern hemisphere had a captivating visitor in the form of the comet C/2024 G3 (ATLAS). It looks magnificent in this Picture of the Week by Juan Beltrán, one of our engineers, who took it on 20 January at our Paranal Observatory in Chile. Just last year, another comet was also caught on camera visiting ESO Headquarters in Garching bei München, Germany. These so-called non-periodic comets only stick around in our skies for a few weeks. If you miss your photo opportunity, your next chance may be a few thousand years later…

As comets approach the Sun they warm up, and the ice in them sublimates, meaning it goes directly from solid ice to gas. Dust particles are also released, and the solar wind and radiation push this gas and dust away from the Sun, creating extended tails. Although astronomers can calculate and estimate how long a comet will be visible, sometimes they surprise us, either by disappearing sooner, or by actually surviving their trip near the Sun relatively intact, saving their typical tail of gas and dust.

For C/2024 G3 (ATLAS) that tail may fade quickly. The comet reached perihelion — the point where it is closest to the Sun — on 13 January 2025. At that point, it was only 13 million kilometers away from our star. But it is now moving away, and there are signs that the nucleus might have fragmented even though the tail is still visible. If you are in the southern hemisphere you can still try to catch it towards the west after sunset; otherwise check our webcams!