Interstellar Comet 3I/ATLAS: Latest NASA, ESA and UN Updates on the 3I ATLAS Comet (30 November 2025)

Published: 30 November 2025

Interstellar comet 3I/ATLAS – also known as C/2025 N1 (ATLAS) or simply the 3I ATLAS comet – is racing out of the inner solar system after a dramatic swing around the Sun. It’s only the third known object ever seen entering our neighbourhood from another star system, and it has triggered an unprecedented response from NASA, ESA and the United Nations. ^[1]

As of 30 November 2025, 3I/ATLAS is:

Confirmed to be an interstellar comet, not an alien spacecraft.
The focus of a UN‑backed planetary‑defence exercise led by the International Asteroid Warning Network (IAWN). ^[2]
Being tracked by dozens of spacecraft and telescopes across the solar system. ^[3]
Past its closest approach to the Sun (perihelion) on 30 October 2025 and heading back outward. ^[4]
On course to pass no closer than ~170 million miles (≈270 million km) from Earth on 19 December 2025 – safely distant. ^[5]

Below is where things stand today: what 3I/ATLAS is, what the latest data show and why the world has turned this icy visitor into a full‑scale test of planetary defence.

Key facts about the 3I ATLAS comet

Designation: 3I/ATLAS (C/2025 N1)
Type: Interstellar comet (3rd known interstellar object, after 1I/‘Oumuamua and 2I/Borisov) ^[6]
Discovery: 1 July 2025 by the ATLAS (Asteroid Terrestrial‑impact Last Alert System) telescope in Rio Hurtado, Chile – part of NASA’s planetary‑defence network. ^[7]
Orbit: Strongly hyperbolic, eccentricity ≈ 6.14 – it’s not bound to the Sun and will never return. ^[8]
Size: Nucleus diameter estimated between ~440 m and 5.6 km based on Hubble images. ^[9]
Speed: Entered the solar system moving ~137,000 mph (221,000 km/h); sped up to ~153,000 mph (246,000 km/h) near the Sun. ^[10]
Perihelion (closest to Sun): 30 October 2025, at about 1.4 AU (≈130 million miles / 210 million km), just outside Mars’ orbit. ^[11]
Closest to Earth: Expected on 19 December 2025, at roughly 1.8 AU (≈269–270 million km) – almost twice the Earth–Sun distance. ^[12]
Where it is today (30 Nov 2025): In the constellation Virgo, about 1.9 AU from Earth with an observed magnitude around 10–11, visible only with a decent telescope or strong binoculars. ^[13]

What is interstellar comet 3I/ATLAS?

3I/ATLAS is a dirty snowball from another planetary system. Astronomers recognised it as interstellar almost immediately after its discovery, thanks to its unusually high speed and sharply hyperbolic orbit, which cannot be explained if it were born in our own solar system. ^[14]

NASA’s official fact sheet notes that:

3I/ATLAS is only the third known object to pass through our system from interstellar space.
Its orbit is so open that it’s described as a hyperbolic fly‑through, not a closed ellipse like normal comets.
It will eventually head back into interstellar space at roughly the same speed it arrived with, after its brief detour near the Sun. ^[15]

Because the ATLAS telescope is part of NASA’s planetary defence network, the object was quickly checked for potential impact risk. Calculations confirmed that 3I/ATLAS would never come particularly close to Earth, a conclusion reiterated by NASA during its recent press briefing and on its dedicated 3I/ATLAS pages. ^[16]

A solar‑system‑wide observing campaign

One of the biggest stories around the 3I ATLAS comet is the sheer number of spacecraft watching it.

NASA describes 3I/ATLAS as the focus of an “unprecedented solar system‑wide observation campaign”, with a dozen NASA assets (and several ESA missions) collecting images or data since July. ^[17]

Key highlights:

From Earth orbit & beyond
- Hubble Space Telescope: constrained the nucleus size to roughly 0.4–5.6 km and captured early images of a pear‑shaped coma. ^[18]
- James Webb Space Telescope (JWST): recorded a high ratio of carbon dioxide to water in the comet’s ices, unusual compared with “home‑grown” comets. ^[19]
- SPHEREx (a new all‑sky infrared surveyor) also observed the comet for about a week in August, adding spectral data on its ices and dust. ^[20]
From Mars
- Mars Reconnaissance Orbiter (MRO) captured one of the closest detailed images on 2 October 2025 when the comet passed about 19 million miles (30 million km) from Mars. ^[21]
- MAVEN observed the hydrogen cloud around 3I/ATLAS in ultraviolet, helping to measure how much water is being blown off. ^[22]
- The Perseverance rover even snagged a faint glimpse from the surface of Mars, seeing the comet as a tiny smudge in the night sky. ^[23]
Sun‑watching missions
- STEREO and the joint ESA/NASA SOHO spacecraft managed to detect 3I/ATLAS as it whipped past the Sun, despite expectations it would be too faint. These missions stacked multiple frames to reveal the comet as a subtle brightening in the data. ^[24]
- PUNCH, a newer heliophysics mission, imaged the comet’s tail from September 20 to October 3. ^[25]
Asteroid missions en route elsewhere
- NASA’s Psyche spacecraft acquired several images over eight hours in early September from about 33 million miles away.
- Lucy, on its way to Jupiter’s Trojan asteroids, captured the comet and its tail from around 240 million milesaway. ^[26]
ESA’s Mars orbiter triangulation
- ESA’s ExoMars Trace Gas Orbiter watched the comet between 1–7 October and, by combining that view with Earth‑based data, improved the predicted path of 3I/ATLAS by a factor of ten – a crucial result for future planetary‑defence work. ^[27]

In short: the 3I ATLAS comet is being tracked from all angles – from the inner solar system to Mars and beyond – giving scientists a 3D view of an interstellar object we’ve never had before.

What the data say: size, speed and strange chemistry

How big is 3I/ATLAS?

Because the nucleus is hidden inside a bright cloud of gas and dust, no telescope has cleanly resolved it yet. Hubble’s July images were used to set an upper and lower bound:

Minimum diameter: ~440 metres
Maximum diameter: ~5.6 kilometres ^[28]

That places 3I/ATLAS somewhere between a medium‑sized city block and a small mountain, similar in scale to many ordinary comets.

How fast is it going?

On arrival in July, 3I/ATLAS was racing into the solar system at about 137,000 mph (221,000 km/h). Near perihelion, its speed rose to roughly 153,000 mph (246,000 km/h) under the Sun’s gravity. After it leaves, it will cruise back into interstellar space at about the same inbound speed. ^[29]

What is it made of?

Here things get especially interesting.

Carbon dioxide fog: JWST and other instruments show a CO₂‑rich coma, with a higher CO₂‑to‑water ratio than is typical for many solar‑system comets. ^[30]
Unusual metals: Spectra reveal gas unusually rich in nickel relative to iron, again somewhat different from many local comets but still within natural variation. ^[31]
Dust behaviour: Early in its approach, dust seemed to be blown toward the Sun‑facing side before radiation pressure finally sculpted a more traditional tail pointing away. That unusual sequence probably reflects the dominance of relatively large, slow‑moving dust grains. ^[32]

Combined, these findings suggest that 3I/ATLAS may have formed in a colder, older and more heavily irradiated star system than our own – but still behaves, chemically, like a comet rather than anything exotic. ^[33]

Tails, anti‑tails and the “changing colour” saga

Many tails and a dramatic anti‑tail

Amateur and professional images alike show 3I/ATLAS displaying multiple tails, including an eye‑catching anti‑tail that appears to point toward the Sun rather than away from it. ^[34]

Sky & Telescope reports that this is best explained by large dust grains ejected sunward from the hot daytime hemisphere of the nucleus. These grains are heavy enough that solar radiation pressure pushes them only slowly, so for a while the dust structure points roughly back toward the Sun before eventually being swept into a more conventional tail. ^[35]

Interstellar or not, this behaviour is weird‑looking but not unprecedented; similar anti‑tails have been seen in several solar‑system comets.

Did 3I/ATLAS really change colour three times?

One of the most viral storylines has been that 3I/ATLAS has “changed colour” multiple times: red in July, green in September, then blue after perihelion. A widely shared report in early November pulled together observations suggesting a new bluish hue after an unexpected brightening behind the Sun. ^[36]

However, follow‑up coverage – including interviews with one of the scientists behind the colour study – urges much more caution:

Space.com notes that the study’s description of the comet as “distinctly bluer than the Sun” refers to the gas coma’s overall tint, not a dramatic, confirmed time‑varying colour change.
The same scientist stresses that, as far as the data now show, the gas coma has been blue‑green since it became prominent, and there is no strong evidence that the gas itself has flipped between multiple colours. ^[37]

Much of the apparent colour‑shifting is likely due to:

Different filters and exposure times used by telescopes and astrophotographers.
Changing relative contributions of gas vs. dust as the comet gets more active. ^[38]

So, yes, the 3I ATLAS comet can appear redder, greener or bluer in various images – but the scientific consensus right now is that we don’t yet have solid evidence of repeated, dramatic physical colour changes in the way the headlines suggest.

Alien spacecraft or icy snowball? The controversy and the consensus

Because 3I/ATLAS is unusual and interstellar, it was almost inevitable that alien‑probe speculation would appear.

Harvard astrophysicist Avi Loeb and collaborators have argued in blog posts and preprints that the comet’s anti‑tail and measured non‑gravitational acceleration (small deviations from a pure gravity‑only path, likely caused by outgassing) might be easier to explain if the object were using technological thrusters rather than natural jets of vaporising ice. ^[39]

Those ideas have been widely reported – and heavily debated. But major space agencies have been extremely clear about their interpretation:

In a high‑profile briefing summarised by Space.com, NASA officials stated unambiguously that “3I/ATLAS is a comet” and emphasised that nothing in the data shows technosignatures or behaviour requiring alien technology as an explanation. ^[40]
Coverage in outlets such as National Geographic, Hindustan Times and Live Science likewise presents the alien‑craft hypothesis as a minority, speculative view, contrasting it with the broader scientific consensus that 3I/ATLAS is behaving like a somewhat quirky, but natural, comet. ^[41]

In other words: there is currently no evidence that 3I/ATLAS is anything other than an interstellar comet, and the burden of proof for extraordinary claims remains very high.

A live planetary‑defence drill: UN, IAWN and the 3I/ATLAS campaign

One of the most important new developments in late November is that 3I/ATLAS has been formally adopted as the target of a global planetary‑defence exercise coordinated through the United Nations.

What the campaign is

The International Asteroid Warning Network (IAWN) has launched a “Comet Astrometry Campaign” using 3I/ATLAS as a live test case from 27 November 2025 to 27 January 2026. ^[42]

According to IAWN’s official campaign page and UN‑linked communications:

This is the 8th IAWN observing exercise since 2017.
The goal is to train the global community to extract accurate positional measurements (astrometry) from tricky comet images, where fuzzy comae and tails can shift the apparent centre of light. ^[43]
The exercise includes workshops, a mid‑campaign check‑in and a final teleconference in early February 2026. ^[44]

Media reports from Gulf News and Times of India emphasise that this is not a response to any threat: 3I/ATLAS poses no danger to Earth. Instead, it’s a rehearsal of how the world would coordinate if a future comet or asteroid were on a risky trajectory. ^[45]

Why choose an interstellar comet?

From a planetary‑defence perspective, 3I/ATLAS is perfect practice material:

It’s bright enough and visible long enough for observatories around the world to participate.
Its cometary coma and tail make astrometry more challenging, forcing teams to refine real‑world techniques. ^[46]
Being interstellar and high‑profile, it naturally attracts more telescopes – ideal for stressing and testing global coordination.

In effect, the 3I ATLAS comet has become a live‑fire drill for the planet’s defence systems, even though the object itself is harmless.

How and when to see 3I/ATLAS

If you’re hoping to actually see the 3I ATLAS comet, here’s the status as of 30 November 2025:

The comet is currently located in Virgo, about 1.9 AU from Earth, with a brightness around magnitude 10.4according to the latest observational databases. ^[47]
It will make its closest pass to Earth on 19 December 2025, at about 1.8 AU distance – still far beyond naked‑eye visibility. ^[48]
Articles aimed at skywatchers consistently stress that 3I/ATLAS is not a spectacle like a great naked‑eye comet; you’ll need a serious amateur telescope or powerful binoculars and dark skies to have a chance of spotting it. ^[49]

Because its exact rise and set times depend on where you live, observers should rely on up‑to‑date sky charts or appsthat incorporate the latest ephemerides (for example, services that pull data from JPL Horizons, COBS or TheSkyLive). ^[50]

Even if you never see it with your own eyes, though, 3I/ATLAS is being imaged so extensively that there is already a growing gallery of professional and amateur pictures – and many more are expected around its December closest approach. ^[51]

Why 3I/ATLAS matters so much

A fossil from another star system

Based on its inbound speed and orbit, scientists think 3I/ATLAS was likely ejected from its home system billions of years ago, possibly from the outer regions of a very old star system on the Milky Way’s outskirts. ^[52]

Early polarimetric and photometric studies hint that:

Its dust and surface properties may differ from both 1I/‘Oumuamua and 2I/Borisov.
It could represent a new class of interstellar comet, expanding the diversity of objects we know can roam between stars. ^[53]

This makes 3I/ATLAS a kind of time capsule from a long‑ago star system, potentially older than the Sun itself.

A testbed for future interstellar visitors

Because 3I/ATLAS arrived while our observatories and spacecraft fleet are more capable than ever, it is also a dress rehearsal for how we will study future interstellar objects:

Coordinated, multi‑mission campaigns from Mars, Earth orbit and deep‑space missions. ^[54]
Rapid‑response planetary‑defence drills under UN frameworks. ^[55]
Sophisticated modelling to distinguish natural outgassing from any truly anomalous behaviour. ^[56]

Whatever happens with the remaining observations, the story of the 3I ATLAS comet is already reshaping how we think about interstellar visitors, global cooperation and the practicalities of protecting Earth.

For now, the message from space agencies is simple: 3I/ATLAS is a fascinating, interstellar comet – not a threat – and one of the best natural laboratories we’ve ever had for studying worlds beyond our own.