Interstellar objects

[bolun]

NASA Discovers Interstellar Comet Moving Through Solar System

On July 1, the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, first reported observations of a comet that originated from interstellar space. Arriving from the direction of the constellation Sagittarius, the interstellar comet has been officially named 3I/ATLAS. It is currently located about 420 million miles (670 million kilometers) away.

Since that first report, observations from before the discovery have been gathered from the archives of three different ATLAS telescopes around the world and the Zwicky Transient Facility at the Palomar Observatory in San Diego County, California. These “pre-discovery” observations extend back to June 14. Numerous telescopes have reported additional observations since the object was first reported.

The comet poses no threat to Earth and will remain at a distance of at least 1.6 astronomical units (about 150 million miles or 240 million km). It is currently about 4.5 au (about 416 million miles or 670 million km) from the Sun. 3I/ATLAS will reach its closest approach to the Sun around Oct. 30, at a distance of 1.4 au (about 130 million miles or 210 million km) — just inside the orbit of Mars.

The interstellar comet’s size and physical properties are being investigated by astronomers around the world. 3I/ATLAS should remain visible to ground-based telescopes through September, after which it will pass too close to the Sun to observe. It is expected to reappear on the other side of the Sun by early December, allowing for renewed observations.

https://science.nasa.gov/blogs/planetary-defense/2025/07/02/nasa-discovers-interstellar-comet-moving-through-solar-system/

Image credit: NASA/JPL-Caltech

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Related thread: 2I/Borisov

https://forum.nasaspaceflight.com/index.php?topic=49027.0

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Edit: Thread title changed on request by Blackstar. (07/05/2025)

[bolun]

ESA observes interstellar comet 3I/ATLAS

Astronomers from ESA’s Near-Earth Object Coordination Centre (NEOCC), part of the Agency’s Planetary Defence Office, made these observations of the newly discovered interstellar comet 3I/ATLAS on 2 July 2025.

The comet is only the third of its kind ever observed, following the famous 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.

It was first spotted on 1 July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile. Its unusual trajectory immediately raised suspicions that it originated from interstellar space. This was later confirmed by astronomers around the world, and the object was given its formal designation: 3I/ATLAS, indicating its status as the third known interstellar object.

As of 3 July, 3I/ATLAS is approximately 670 million kilometres from the Sun and will make its closest approach in late October 2025, passing just inside the orbit of Mars. It is thought to be up to 20 kilometres wide and is travelling roughly 60 km/s relative to the Sun. It poses no danger to Earth, coming no closer than 240 million kilometres – over 1.5 times the distance between Earth and the Sun.

The observations were made using the Las Cumbres Observatory telescope in Hawaii, one of the telescopes on which ESA astronomers are allocated dedicated observing time.

Related article: ESA tracks rare interstellar comet

https://www.esa.int/ESA_Multimedia/Images/2025/07/ESA_observes_interstellar_comet_3I_ATLAS

Image credit: ESA / Las Cumbres Observatory

[JulesVerneATV]

We are finding more of these interstellar interlopers, a different study to the outer solar system Oort cloud  2,000 to 200,000 AU with some comets with their farthest retreat seeming to cluster around 20,000 AU or known Kuiper belt objects

There is ʻOumuamua and 2I/Borisov also
https://web.archive.org/web/20210623185932/https://www.eurekalert.org/pub_releases/2019-10/aoju-icw101119.php
,
https://www.sciencenews.org/article/astronomy-interstellar-comet-space

[bolun]

Maybe the title of this thread should be interstellar objects? 3I/ATLAS will go away, but there will be more of these.

Done 

[bolun]

3I/ATLAS: The IAC is monitoring closely the third interstellar object detected in the Solar System

Combined image of interstellar comet 3I/ATLAS formed by 239 exposures of 50 seconds taken with the Two-metre Twin Telescope (TTT3) at the Teide Observatory. The brightness contours are superimposed on the comet. The apparent size in the sky is 9.8‘ x 8.8’, which corresponds to a cloud of gas and dust about 25,000 km long and 22,400 km wide. The image shows the orientation, scale and directions in which the Sun is located and in which the object is moving. This image is the result of joint work by the TTT science group and the solar system and low surface brightness groups of the Instituto de Astrofísica de Canarias

https://www.iac.es/en/outreach/news/3iatlas-iac-monitoring-closely-third-interstellar-object-detected-solar-system

Image credit: IAC (Miguel R. Alarcon, M. Serra-Ricart, J.Licandro, Sergio Guerra Arencibia, Ignacio Ruiz Cejudo, Ignacio Trujillo)

[catdlr]

Scott Manley - We just discovered the fastest interstellar comet - 150,000 Miles Per Hour:

[catdlr]

NASA: What We Know About Interstellar Comet 3I/ATLAS:

[LouScheffer]

Without trying super hard, we've found 3 such objects in 8 years.  This means they are not rare.

And we'd expect Rubin to pick up the pace.  Compare to Atlas, the previous high-cadence champion, Rubin has roughly 144x more light gathering power.  (6 meter equivalent aperture compared to 0.5 meter).  How this plays out depends on the size distribution of interstellar objects, and how close they come to the Sun.

For objects of constant size, Rubin can see them up to 144^(1/4) = 3.46 times further from the sun (inverse square both ways, like radar).  That's about a 40x larger volume.

For objects at the same distance, Rubin should be able to see objects with 1/12 the radius of Atlas.  And if these things are anything like asteroids in general, there are lots more small ones than big ones, maybe a factor of 30 for a radius difference of 12x. 

Given just these two points, I'll go out on a limb and state the Rubin will find at least 30x more of these things than Atlas.  Since Atlas has found one in its 10 years of operation, I'm guessing Rubin will find at least 3 per year.

EDIT:  This simple back-of-the-envelope calculation is reasonably close to that of the much more sophisticated esrimates below, what are roughly 1.5 objects per year.

[jebbo]

The estimated detection rate for Rubin is here:

https://arxiv.org/abs/2109.10406

A useful population estimate:
https://arxiv.org/abs/2402.04904

A study on whether they are in streams and whether Rubin can resolve this:
https://arxiv.org/abs/2411.14577
https://arxiv.org/abs/2502.16741

--- Tony

[Star One]

Two new papers suggest that 3I/ATLAS is probably from an old star in the thick disc of our galaxy, and is possibly older than our solar system has existed.

https://www.iflscience.com/new-interstellar-comet-tracked-to-its-origin-region-its-much-older-than-the-solar-system-79917

[bolun]

Mystery interstellar object could be oldest known comet (BBC)

https://www.bbc.com/news/articles/cx23g5jpj9go

Third ever detection of interstellar object (University of Oxford)

https://www.physics.ox.ac.uk/news/third-ever-detection-interstellar-object

From a Different Star: 3I/ATLAS in the context of the Ōtautahi-Oxford interstellar object population model (Cornell University)

https://arxiv.org/abs/2507.05318

[Blackstar]

https://noirlab.edu/public/news/noirlab2522/

[Star One]

Avi Loeb is at it again.

In a new, yet-to-be-peer-reviewed paper, Harvard astronomer Avi Loeb — the same scientist who suggested that 'Oumuamua, the first interstellar object ever detected back in 2017, was alien in nature — teamed up with researchers from the Britain-based Initiative for Interstellar Studies to hypothesize not only that the newly-discovered interloper 3I/ATLAS is alien in origin, but that it may be from a hostile civilization, too.

https://futurism.com/harvard-paper-interstellar-object-alien

Paper linked to in article.

[Blackstar]

https://thespacereview.com/article/5020/1


It’s the end of the world as we know it (and I feel fine): The persistence of the alien invasion film
by Dwayne Day
Monday, July 7, 2025

A few days before July 4, a telescope detected a massive object heading from deep space into the inner solar system. That’s the start of the 1996 alien invasion flick Independence Day. It also happened last week, when the University of Hawaii’s NASA-funded ATLAS telescope in Chile detected an object, later classified as 3I/ATLAS, the “I” standing for “interstellar.” This was only the third time an interstellar comet has been detected passing through our solar system, after the much more famous and lyrical ’Oumuamua was discovered in 2017, and then 2I/Borisov in 2019. Better telescopes will certainly detect many more.

Every time this happens, people speculate that the object is a spaceship, possibly part of an invasion fleet. Alien invasions have lurked below the surface of the American psyche for over seven decades now. And by total coincidence, on the same day that 3I/ATLAS received its designation, Apple TV+ released the trailer for the third season of its alien invasion show Invasion, which you have almost certainly never heard of, let alone watched. Invasion has all the characteristics of modern shows of its ilk: some clever ideas, uninspired execution including wobbly CGI, lots of screaming, and no idea where it is going or how the story will end. But it helps shine a light on how space is part of our culture, and our unease about it.

[Apollo22]

Avi Loeb is at it again.

In a new, yet-to-be-peer-reviewed paper, Harvard astronomer Avi Loeb — the same scientist who suggested that 'Oumuamua, the first interstellar object ever detected back in 2017, was alien in nature — teamed up with researchers from the Britain-based Initiative for Interstellar Studies to hypothesize not only that the newly-discovered interloper 3I/ATLAS is alien in origin, but that it may be from a hostile civilization, too.

https://futurism.com/harvard-paper-interstellar-object-alien

Paper linked to in article.

Oh gosh, will that idiot Loeb push the same self-agrandizing narrative each time a interstellar object is discovered ? 

[matthewkantar]

Loeb is Harvard’s Chicken Little. An embarrassment to science, if not humanity.

[Hyperborealis]

Come on. People should just read Loeb's paper. He recognizes the great likelihood the object is merely a comet: "By far the most likely outcome will be that 3I/ATLAS is a completely natural interstellar object, probably a comet, and the authors await the astronomical data to support this likely origin." He offers the Dark Forest hypothesis merely as a "testable hypothesis, to which the authors do not
necessarily ascribe."

He brings forward his his outlandish hypothesis as a way to highlight the object's various anomalous characteristics,  and generally to set up an epistemological question: "is an outlier of a sample a consequence of expected random fluctuation, or is there ultimately a sound reason for its
observed discrepancy?” As he points out, given that the sample size of interstellar objects is three, we lack an empirical basis upon which to stand a conventional assumption as to what the object is.

Also, and not least, the article is fun to read, interesting, and stretches the mind. It makes science and astronomy appealing, which is all to Loeb's credit. People should ignore the naysayers, and read the article for themselves.

[sstli2]

A good commentary on this Loeb nonsense: https://sites.psu.edu/astrowright/2025/07/18/avi-and-3i-atlas/

[MickQ]

Just curious.  With the three objects spotted so far, are their trajectories in any way similar or are they vastly different ?

[MickQ]

Just curious.  With the three objects spotted so far, are their trajectories in any way similar or are they vastly different ?

Are you thinking of "Rendezvous with Rama"? They come in three.

Not initially, but now that you mention it 🤔

I was thinking that if they all came from the same general direction then maybe they were all the product of some ancient cataclysm like a planet killer event somewhere.  A sample retrieval mission would be awesome.  Just watch out for anything blue.