NASA’s new multi-mission images shed light on the comet’s ancient, interstellar origins.
Credit: Jay Nlper on Unsplash
A solar system-wide observation campaign has given scientists their clearest view yet of interstellar comet 3I/ATLAS, revealing new clues about its chemistry, its origin, and why the object has sparked weeks of speculation.
From mysterious signals and alien speculation to a complete portrait
For the past month, the world has been following the journey of 3I/ATLAS – the third interstellar object ever detected in our solar system and by far the most puzzling. It has been blamed for mysterious radio signals, unexplained acceleration and drawn comparisons with “alien probes”.
Now, after a coordinated release of new imagery and data, NASA has delivered the most complete portrait of the object so far. The agency’s “multiple lenses” campaign combines observations from a dozen spacecraft and telescopes, creating a layered, multi-wavelength view that confirms 3I/ATLAS is a natural interstellar comet with unusually complex behaviour.
The update also reiterates that the comet poses no threat to Earth. NASA’s latest trajectory shows it will pass safely and closest to Earth about Friday December 19 at roughly 267 million kilometres – nearly twice the distance between our planet and the Sun.
Twelve “eyes” tracking a one-time visitor
What makes the new release extraordinary is the sheer number of instruments involved. NASA says spacecraft across the solar system – from Mars to Earth to solar orbit – have captured the comet from different angles and wavelengths.
From Mars, the orbiters MRO (Mars Reconnaissance Orbiter) and MAVEN (Mars Atmosphere and Volatile EvolutioN mission) photographed 3I/ATLAS during its approximately 29-million-kilometre flyby, revealing a bright nucleus surrounded by active gas jets.
From solar orbit, the SOHO (Solar and Heliospheric Observatory) and STEREO (Solar TErrestrial RElations Observatory) missions tracked the development of its tail as it interacted with the solar wind.
From Earth’s neighbourhood, NASA’s ATLAS survey telescope – which discovered the comet in July – and the Hubble Space Telescope traced its changing brightness and colour as it approached the Sun.
This broad effort results in a gallery of images that may look simple at first glance, but each wavelength reveals something different: heat signatures, dust grain structures, outgassing chemistry and even the behaviour of the comet’s magnetic environment.
An icy body shaped by cosmic rays
One of the most significant discoveries comes from spectroscopy – breaking down the comet’s light to identify its chemical ingredients.
Data from the James Webb Space Telescope and NASA’s SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission show that 3I/ATLAS contains an unusually high amount of carbon dioxide.
Researchers found a CO₂-to-water ratio of about 7.6 to 1, vastly higher than the ratios seen in typical comets formed in our own solar system. They also detected elevated levels of carbon monoxide (CO) and smaller traces of other gases like carbonyl sulphide.
This chemistry is consistent with ices that have been bombarded for millions or billions of years by galactic cosmic rays. The radiation slowly alters the outer layers of the comet, producing the distinctive chemical signature scientists are now seeing.
The findings match earlier observations that suggested the comet’s greenish glow, sudden colour changes and early brightening were tied to an irradiated, processed icy surface – unlike the fresher surfaces of comets that formed with our Sun.
Radio waves confirm a natural origin
The new observations also settle one of the most debated questions: the comet’s mysterious radio signals.
Earlier in November, astronomers using the MeerKAT radio array in South Africa detected hydroxyl (OH) emissions at 1.665 and 1.667 gigahertz. These radio lines form when sunlight breaks apart water molecules released from a comet’s nucleus – a textbook signature of natural water outgassing.
This detection strongly counters theories that 3I/ATLAS might be artificial. A manufactured object would not produce molecular fingerprints linked to evaporating ice.
Combined with the new imagery, scientists say the case is now firmly in favour of a natural – if highly unusual – interstellar comet.
A relic from before the Sun was born
Dynamical modelling and chemical clues suggest 3I/ATLAS formed in a much older star system, possibly several billion years older than our own, before being ejected into interstellar space.
Telescopes estimate the nucleus may be between a few hundred metres and about five kilometres across – significantly larger than previous interstellar objects 1I/ʻOumuamua and 2I/Borisov.
The comet reached its closest point to the Sun in late October and is now retreating toward the outer solar system. It will pass closest to Earth on December 19 at a safe distance before fading from view, never to return.
A once-in-a-lifetime window into another world
NASA’s new data turns 3I/ATLAS from a speculative mystery into a scientific treasure. Instead of a smooth, pristine snowball, the comet appears coated in ancient ice reshaped by cosmic rays over unimaginable timescales.
As it sweeps past our Sun on its single visit, it offers a rare opportunity to directly sample the building blocks of a different solar system, forged long before our own star ever lit up the sky.
