Interstellar comet 3I/ATLAS spewed 70 swimming swimming pools of water day-after-day because it flew previous the Sun

The European Space Agency’s Juice mission – its Jupiter Icy Moons Explorer – is presently on its strategy to Jupiter and set to reach there in 2031.

Once there, Juice will discover the fuel big’s massive icy moons for indicators of life within the liquid oceans hidden beneath their frozen crusts.

But in November 2025, mission scientists bought Juice to analyse a really totally different supply of water: that of the vapour streaming from comet 3I/ATLAS because it flew near the Sun.

3I/ATLAS and its photo voltaic shut method

Comet 3I/ATLAS is an interstellar comet that was found on 1 July 2025.

It’s ‘interstellar’ as a result of it fashioned in a distinct a part of the Galaxy, past our Solar System. It’s one in all solely three such our bodies ever found.

The comet entered our Solar System from deep house, then flew previous Earth and the Sun, and is now on its means out of the Solar System. Once it exits our Solar System, will probably be gone from our view perpetually.

3I/ATLAS is regarded as a minimum of 7 billion years previous, making it probably the oldest comet ever found.

In late October 2025, 3I/ATLAS made its shut method to the Sun, zooming previous the star on the centre of our Solar System, and heating up because it did so.

Juice sees 3I/ATLAS’s highly effective outburst

In November 2025, the Juice spacecraft noticed interstellar comet 3I/ATLAS simply after the comet’s method to the Sun.

Comets are made up of mud and ice, and after they cross near our Sun, that ice sublimates into vapour, inflicting a fuzzy coma to seem across the comet’s head and a path to comb behind it.

The European Space Agency mission operations group turned on 5 of Juice’s science devices to assemble information on how the energetic comet was behaving because it flew by our Sun.

It took three months to obtain that information, and now scientists are engaged on analysing the information to study extra concerning the comet.

They discovered that, on 2 November 2025, 4 days after 3I/ATLAS made its closest method to the Sun, the comet was spewing out 2,000kg of water vapour each second.

That’s the identical as 70 Olympic swimming swimming pools per day, in line with the science group.

They say the quantity of water vapour leaving 3I/ATLAS is “not exceptional”, however is greater than seen in some comets after they method the Sun.

The Juice spacecraft then detected 3I/ATLAS once more on 12 and 19 November 2025 because it was transferring away from the Sun.

By 12 November, the group say, the quantity of water vapour launched by 3I/ATLAS had not lowered considerably.

Spewing water in direction of the Sun

The Juice spacecraft’s Submillimeter Wave Instrument detected water vapour coming from 3I/ATLAS, and that the majority of it was launched from the Sun-facing aspect of the comet.

Scientists say it seems a lot of the water vapour will not be coming instantly from the comet’s nucleus, i.e. the stable half. Instead, it is coming from icy mud grains which have escaped into the coma.

What’s extra, this information can inform the group extra about the kind of atmosphere through which 3I/ATLAS fashioned.

The science group have been evaluating how a lot ‘gentle water’– regular H2O – has been coming from 3I/ATLAS with how a lot ‘semiheavy water’ (HDO), the latter having been measured by the European Southern Observatory’s ALMA telescopes in Chile and the James Webb Space Telescope.

They say this ratio can provide them details about how and the place an object fashioned.

The ratio is extraordinarily excessive in 3I/ATLAS, which might be a sign that it was born in a chilly, historic nook of the Galaxy and was uncovered to plenty of ultraviolet radiation from younger stars.