Comet 3I/ATLAS – regularly requested questions

What is comet 3I/ATLAS?

Comet 3I/ATLAS is a newly recognized interstellar object, which means that it comes from exterior our Solar System. It is barely the third of its variety ever noticed, following 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.

 

Why is it vital?

These comets are completely international. Every planet, moon, asteroid, comet and lifeform in our Solar System share a standard origin. But interstellar comets are true outsiders, carrying clues in regards to the formation of worlds far past our personal.

 

When and the way was it detected?

It was first noticed on 1 July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile. Its uncommon trajectory instantly raised suspicions that it originated from interstellar house. This was later confirmed by astronomers world wide, and the item was given its formal designation: 3I/ATLAS.

 

Why the title ‘3I/ATLAS’? 

Traditionally, comets had been named after the one that found them. Nowadays, we observe a coded naming system developed by the International Astronomical Union. The first letter signifies the class that the comet falls below – on this case ‘I’ for ‘Interstellar’. The quantity ‘3’ earlier than the ‘I’ signifies that the comet is the third of its variety. The phrase ‘ATLAS’ refers back to the programme that operates the telescope that first noticed the comet. 

Find out extra about how comets are named right here. 

 

Can you give some fast information in regards to the comet? 

Size: a number of hundred metres to some kilometres throughout 

Speed: roughly 210 000 km/h – the very best ever recorded for a Solar System customer 

Age: billions of years previous – indicated by its breathtaking velocity, proof that it has been drifting by means of house for a really very long time 

Closest strategy to Earth: 240 million km 

Closest strategy to Mars: 30 million km 

 

Does it pose a hazard to Earth?

The comet will come no nearer than 240 million km – that’s over 1.5 instances the gap between Earth and the Sun. During its closest strategy to the Earth, will probably be on the opposite facet of the Sun. It poses no hazard to our planet or some other planets within the Solar System.

 

Is ESA’s Planetary Defence Office monitoring the comet?

Yes. ESA’s Planetary Defence Office responded promptly to the invention, with ESA astronomers contributing to international efforts to trace the comet’s path utilizing telescopes in Hawaii, Chile and Australia. They are additionally on the lookout for proof of its existence in older information – a course of referred to as ‘precovery’.

These efforts are a part of ESA’s broader mission to detect, monitor, and characterise near-Earth objects – although 3I/ATLAS is just not thought-about one, resulting from its distance from our planet.

By the time the comet reaches its closest level to Earth, will probably be hidden behind the Sun. It is because of reappear in late November, providing astronomers one other window for research.

 

What will occur to 3I/ATLAS within the coming months?

3I/ATLAS is an lively comet. Observations by the NASA/ESA Hubble Space Telescope already seize a mud plume ejected from the Sun-warmed facet of the comet, and the trace of a mud tail streaming away from its nucleus. Comets originating inside our personal Solar System show related behaviour. 

As the comet continues to strategy the Sun, it’s going to doubtless lose an increasing number of mass as frozen gases remodel into vapour, carrying mud and ice into house. Observations by the NASA/ESA/CSA James Webb Space Telescope of the coma, or ‘halo’, surrounding the comet already reveal carbon dioxide, water, carbon monoxide, carbonyl sulphide and water ice being launched because the comet heats up. 

Find out extra in regards to the construction of a comet right here.

 

Is ESA planning to go to 3I/ATLAS?

The comet will make its closest strategy to the Sun in late October 2025, passing simply contained in the orbit of Mars. After that second, it’s going to velocity away from us. This is way too quickly, and the comet is transferring far too shortly, to ponder sending a spacecraft to go to or land on it. Instead, we’re observing 3I/ATLAS from a distance with our house telescopes and planetary missions.

 

What ESA missions will observe 3I/ATLAS?

The comet has already been noticed by house telescopes near Earth, together with the NASA/ESA Hubble Space Telescope and the NASA/ESA/CSA James Webb Space Telescope. In the approaching months, ESA will flip interplanetary voyagers reminiscent of Mars Express, ExoMars Trace Gas Orbiter and the Jupiter Icy Moons Explorer (Juice) within the course of the comet to make additional observations with eyes from all around the Solar System. 3I/ATLAS will cross by means of the sphere of view of the ESA/NASA Solar and Heliospheric Observatory (SOHO), however we anticipate it to be a lot too faint to be seen.

 

When and the way will ESA’s Mars’s missions observe 3I/ATLAS?

ESA’s Mars Express and ExoMars Trace Gas Orbiter (TGO) will observe the comet with a number of devices round its closest strategy to Mars on 3 October 2025. On that date, 3I/ATLAS can be round 30 million km from Mars.

The devices turning their eyes to the comet embrace Mars Express’s High Resolution Stereo Camera (HRSC) and ExoMars TGO’s Colour and Stereo Surface Imaging System (CaSSIS) – each cameras which can be usually used to {photograph} the Red Planet. We may also try to measure the spectrum of sunshine from the comet utilizing Mars Express’s OMEGA and SPICAM spectrometers and TGO’s NOMAD spectrometer, although it isn’t sure whether or not the comet and its tail can be vibrant sufficient for a full spectral characterisation.

The observations might give us hints in regards to the unstable exercise and composition of 3I/ATLAS. As Mars Express and ExoMars TGO are designed to picture the martian floor just some hundred to thousand kilometres beneath, we don’t anticipate spectacular photos of a (comparatively) small comet 30 million km away; the comet itself will cowl lower than a pixel within the photos. We anticipate higher photos of the halo of gasoline across the comet and the tail that streams behind it. The success of the observations additionally will depend on how vibrant the comet is because it approaches the Sun, which in flip relies upon largely on how a lot water it accommodates and the way a lot escapes within the type of a tail.

 

When and the way will ESA’s Juice mission observe 3I/ATLAS?

Of all ESA interplanetary spacecraft, the Jupiter Icy Moons Explorer (Juice) is more likely to have the most effective view of 3I/ATLAS in a really lively state. Juice will try observations in November 2025 utilizing a number of devices, together with cameras, spectrometers and a particle sensor. Coordination with NASA’s Europa Clipper mission is being thought-about, specifically to look at utilizing the dual ultraviolet spectrographs (one on every spacecraft). 

As Juice is at present near the Sun, it’s utilizing its essential high-gain antenna as a warmth defend. It is utilizing its smaller medium-gain antenna to ship information again to Earth at a a lot decrease charge. It can be removed from Earth, on the opposite facet of the Sun. Therefore, we don’t anticipate to obtain information from Juice’s observations of 3I/ATLAS till February 2026.

 

Is ESA planning any missions to go to a comet sooner or later?

Following within the footsteps of ESA’s Rosetta mission, which landed on Comet 67P in 2014, ESA is at present growing the next-generation comet mission, Comet Interceptor. Comet Interceptor would be the first mission to go to a comet coming immediately from the outer reaches of the Sun’s realm, carrying materials untouched for the reason that daybreak of the Solar System. It can be attainable – although impossible given their rarity – that Comet Interceptor might go to an interstellar comet.

Find out extra about Comet Interceptor right here.