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3I/ATLAS: Probably NOT an alien interstellar probe

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Swammerdami

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 3I/ATLAS was detected on July 1, 2025, by the NASA-funded ATLAS survey telescope in Chile. Its discovery was a result of ATLAS's routine, systematic scanning of the night sky for near-Earth objects. The object was identified as an interstellar object due to its unusual speed and hyperbolic trajectory. "Observations by the James Webb Space Telescope have shown that 3I/ATLAS is unusually rich in carbon dioxide and contains a small amount of water ice, water vapor, carbon monoxide, and carbonyl sulfide." "The comet originated from interstellar space in the direction of the constellation Sagittarius, near the Milky Way's Galactic Center."

It is one of only three interstellar objects which have been detected "interloping" into the solar system. Of the three, 3I/ATLAS is the largest and fastest-moving. Wikipedia's  Interstellar object tells us "There has been speculation that interstellar interlopers observed in the solar system are extraterrestrial spacecraft, but this been[sic] ruled out." But their 7-year old source states only that there is no evidence that one (1) of the earlier interlopers was an alien spacecraft.

The trajectory of  3I/ATLAS can be seen at on-line orbit viewers. It moves fast, passing Jupiter's orbit June 9 (with Jupiter near opposite side of orbit), making a very close approach (0.1936 AU) to Mars Oct 3, not approaching Earth or even Earth's orbit, but finally making a very close approach (0.39 AU) to Jupiter March 16 of next year. It comes within 0.6494 AU of Venus on November 3 -- about as close as could be achieved, given that it never gets as close as 1.356 AU to the Sun.

For those conspiring about a possible alien probe, there are several reasons to be suspicious:
  • The object's trajectory is tilted 175° (retrograde and inclined 5°) with respect to the ecliptic. Randomly an object has only a 2.8% chance of an inclination so good for its viewing our system. (OTOH, I suppose ssuch a trajectory would be best for OU chanes of even detecting IT.)
  • The object was aimed close to the Sun, and crossed the ecliptic at approximately its closest approach to Sun. I suppose this was no coincidence, just Sun's gravity.
  • The VERY close approaches to Mars and Jupiter (and even Venus) i-- all still in the future -- are a priori very much odds-against. Even if we agree that it is NOT an alien probe, it is remarkable that the largest and fastest interstellar interloper detected so far has "close encounters" about 1 million-to-one odds-against.
  • Comets have "tail" pointing away from Sun, but this object has a tail pointing toward Sun. (This has explanation, but I don't fully understand.)
  • Another puzzling detail I've forgotten.

Don't be disappointed if 3I/ATLAS is not an alien probe hoping to save us. We may be beyond salvation anyway.
 
Breaking News, signal detected coming from the interstellar exploration vehicle;

"The first alien says, "The dominant life forms on the Earth planet have developed satellite-based nuclear weapons."

The second alien asks, "Are they an emerging intelligence?"

The first alien says, "I don't think so, they have aimed at themselves"
 
Rendezvous With Rama

en.wikipedia.org

Rendezvous with Rama - Wikipedia

en.wikipedia.org en.wikipedia.org

Rendezvous with Rama is a 1973 science fiction novel by British writer Arthur C. Clarke. Set in the 2130s, the story involves a 50-by-20-kilometre (31-by-12-mile) cylindrical alien starship that enters the Solar System. The story is told from the point of view of a group of human explorers who intercept the ship in an attempt to unlock its mysteries. The novel won both the Hugo and Nebula awards upon its release, and is regarded as one of the cornerstones in Clarke's bibliography. The concept was later extended with several sequels, written by Clarke and Gentry Lee.
Click to expand...

Looks like it was recently made into a movie.

What dies ET call humans in spaceships? Spam in a can.
 
pood said:
AvI Loeb is talking up the idea that ths is artificial, so you know right off it’s bullshit. :rolleyes:
Click to expand...

I'd never heard of  Avi Loeb but I clicked on a YouTube. His Wikipedia page makes him almost infinitely more qualified than I.

One complaint: He says that on a scale of zero ("just a rock") to ten ("certainly alien probe") 3I/ATLAS is a 4. OK, whatever. Later he clarifies that to mean 40%.

NO!! That is NOT the way estimating probabilities should work, when the numbers are so divergent.

If it were ME then the "scale of 0 to 10" I might use for such wide divergence of opinion might be like
  • 10 - greater than 99.9%
  • 9 - 99% - 99.9%
  • 8 - 91% - 99%
  • 7 - 50% - 91%
  • 6 - 9% - 50%
  • 5 - 1% - 9%
  • 4 - 0.1% - 1%
  • 3 - 0.01% - 0.1%
  • 2 - 0.001% - 0.01%
  • 1 - 0.0001% - 0.001%
  • 0 - less than 1 chance in a million
I introduced this better approach to probability estimation in a Religion thread (and of course was ignored).
I'd say more but the interface interpreted some key as Send, so I'm cleaning up a mess during the edit window.
 
Last edited:
If I understand what Loeb implies, "3, 4 or 5" on a "scale of 0 to 10" would represent 30%, 40%, 50% chance that 3I/ATLAS is an alien spacecraft. That's just SILLY. 30%, 40%, 50% are essentially IDENTICAL estimates from our vantage. And mainstream analysts would all be lumped near zero, with anyone near 0.1 probably viewed as a crackpot.

I do NOT claim Loeb is necessarily wrong, just that his approach to working with probabilities is inept.

Swammerdami said:
NO!! That is NOT the way estimating probabilities should work, when the numbers are so divergent.

If it were ME then the "scale of 0 to 10" I might use for such wide divergence of opinion might be like
Click to expand...

The following is just an example, hastily jotted with the ease of factors of ten.
What is important is to use ODDS (i.e. p ÷ (1-p)) rather than just p, and to depict wide divergence with a logarithmic scale on the Odds.

Swammerdami said:
  • 10 - greater than 99.9%
  • 9 - 99% - 99.9%
  • 8 - 91% - 99%
  • 7 - 50% - 91%
  • 6 - 9% - 50%
  • 5 - 1% - 9%
  • 4 - 0.1% - 1%
  • 3 - 0.01% - 0.1%
  • 2 - 0.001% - 0.01%
  • 1 - 0.0001% - 0.001%
  • 0 - less than 1 chance in a million
I introduced this better approach to probability estimation in a Religion thread (and of course was ignored).
Click to expand...

If analysts are in wide agreement (say, present 63% and 66% as their separate estimates), comparing the results of new adductions is achieved well enough with ordinary arithmetic, e.g. Bayes' formula. But here opinion ranges from 0.001% (mainstream?) to 40% (Loeb). Failure to follow my prescriptions for further manipulations would lead to gibberished results.
 
Swammerdami said:
 3I/ATLAS was detected on July 1, 2025, by the NASA-funded ATLAS survey telescope in Chile. Its discovery was a result of ATLAS's routine, systematic scanning of the night sky for near-Earth objects. The object was identified as an interstellar object due to its unusual speed and hyperbolic trajectory. "Observations by the James Webb Space Telescope have shown that 3I/ATLAS is unusually rich in carbon dioxide and contains a small amount of water ice, water vapor, carbon monoxide, and carbonyl sulfide." "The comet originated from interstellar space in the direction of the constellation Sagittarius, near the Milky Way's Galactic Center."

It is one of only three interstellar objects which have been detected "interloping" into the solar system. Of the three, 3I/ATLAS is the largest and fastest-moving. Wikipedia's  Interstellar object tells us "There has been speculation that interstellar interlopers observed in the solar system are extraterrestrial spacecraft, but this been[sic] ruled out." But their 7-year old source states only that there is no evidence that one (1) of the earlier interlopers was an alien spacecraft.

The trajectory of  3I/ATLAS can be seen at on-line orbit viewers. It moves fast, passing Jupiter's orbit June 9 (with Jupiter near opposite side of orbit), making a very close approach (0.1936 AU) to Mars Oct 3, not approaching Earth or even Earth's orbit, but finally making a very close approach (0.39 AU) to Jupiter March 16 of next year. It comes within 0.6494 AU of Venus on November 3 -- about as close as could be achieved, given that it never gets as close as 1.356 AU to the Sun.

For those conspiring about a possible alien probe, there are several reasons to be suspicious:
  • The object's trajectory is tilted 175° (retrograde and inclined 5°) with respect to the ecliptic. Randomly an object has only a 2.8% chance of an inclination so good for its viewing our system. (OTOH, I suppose ssuch a trajectory would be best for OU chanes of even detecting IT.)
  • The object was aimed close to the Sun, and crossed the ecliptic at approximately its closest approach to Sun. I suppose this was no coincidence, just Sun's gravity.
  • The VERY close approaches to Mars and Jupiter (and even Venus) i-- all still in the future -- are a priori very much odds-against. Even if we agree that it is NOT an alien probe, it is remarkable that the largest and fastest interstellar interloper detected so far has "close encounters" about 1 million-to-one odds-against.
  • Comets have "tail" pointing away from Sun, but this object has a tail pointing toward Sun. (This has explanation, but I don't fully understand.)
  • Another puzzling detail I've forgotten.

Don't be disappointed if 3I/ATLAS is not an alien probe hoping to save us. We may be beyond salvation anyway.
Click to expand...
I mean, it might not even be a "probe" but a whole vessel, if we are in the realm of wild speculation.

The near passes of 3 different planets IS wild, though, TBH.

If I were to design a craft, it would look kind of like this one does. I keep saying the best way to travel is to paint a rock with spores and slap a thruster to it.

Many people familiar with the game Kerbal Space Program will be familiar with the effect of small deflections over vast distances.

This technique allows gravity steering and acceleration over what could be vast periods of time.

Once humans get the fuck over themselves in terms of ditching the human form, it opens up all sorts of flexibility in terms of time.

I would say the most important thing might be to actually check out and see if it leaves anything on that legrange point it's swinging really close to. Like, we should keep at least one of our telescopes on it for that event, if possible.
 
Jarhyn said:
Swammerdami said:
Don't be disappointed if 3I/ATLAS is not an alien probe hoping to save us. We may be beyond salvation anyway.
Click to expand...
I mean, it might not even be a "probe" but a whole vessel, if we are in the realm of wild speculation.

The near passes of 3 different planets IS wild, though, TBH.
Click to expand...

Going with the (wildly unlikely?) scenario that its trajectory was planned, its closeness to the ecliptic is about 15-1 odds against, right? OR is it the case that intruders OFF the ecliptic wouldn't even get noticed by Near Earth surveys. IOW was it detected only because of that closeness; and there may be similar intruders that are overlooked because their trajectory wouldn't threaten Earth?

Jarhyn said:
If I were to design a craft, it would look kind of like this one does. I keep saying the best way to travel is to paint a rock with spores and slap a thruster to it.

Many people familiar with the game Kerbal Space Program will be familiar with the effect of small deflections over vast distances.

This technique allows gravity steering and acceleration over what could be vast periods of time.

Once humans get the fuck over themselves in terms of ditching the human form, it opens up all sorts of flexibility in terms of time.

I would say the most important thing might be to actually check out and see if it leaves anything on that legrange point it's swinging really close to. Like, we should keep at least one of our telescopes on it for that event, if possible.
Click to expand...

Unless the hypothetical aliens have mastered some warp-drive or quantum teleportation, any gift the spacecraft leaves behind would have started decelerating already and could deviate from its mother's trajectory.

For those of us who figure 3I/ATLAS is just a random rock, what IS the most exciting astronomical event to hope for in our lifetimes? Betelgeuse exploding in this century -- is that not a 1% or 2% chance or so?
 
Swammerdami said:
Jarhyn said:
Swammerdami said:
Don't be disappointed if 3I/ATLAS is not an alien probe hoping to save us. We may be beyond salvation anyway.
Click to expand...
I mean, it might not even be a "probe" but a whole vessel, if we are in the realm of wild speculation.

The near passes of 3 different planets IS wild, though, TBH.
Click to expand...

Going with the (wildly unlikely?) scenario that its trajectory was planned, its closeness to the ecliptic is about 15-1 odds against, right? OR is it the case that intruders OFF the ecliptic wouldn't even get noticed by Near Earth surveys. IOW was it detected only because of that closeness; and there may be similar intruders that are overlooked because their trajectory wouldn't threaten Earth?

Jarhyn said:
If I were to design a craft, it would look kind of like this one does. I keep saying the best way to travel is to paint a rock with spores and slap a thruster to it.

Many people familiar with the game Kerbal Space Program will be familiar with the effect of small deflections over vast distances.

This technique allows gravity steering and acceleration over what could be vast periods of time.

Once humans get the fuck over themselves in terms of ditching the human form, it opens up all sorts of flexibility in terms of time.

I would say the most important thing might be to actually check out and see if it leaves anything on that legrange point it's swinging really close to. Like, we should keep at least one of our telescopes on it for that event, if possible.
Click to expand...

Unless the hypothetical aliens have mastered some warp-drive or quantum teleportation, any gift the spacecraft leaves behind would have started decelerating already and could deviate from its mother's trajectory.

For those of us who figure 3I/ATLAS is just a random rock, what IS the most exciting astronomical event to hope for in our lifetimes? Betelgeuse exploding in this century -- is that not a 1% or 2% chance or so?
Click to expand...
It could, but that still means needing to get the thing. I would much rather get as close as possible to a destination before dropping payloads, also potentially because some kind of scans might be on the itinerary.

my goals in a system, if I were to be an alien driving that rock, would be to drop something at a legrange point of a larger outer planet; to fly by the neighborhood of the Goldilocks zone; to fly by the star?

Really, getting so close to the sun is the real thing that makes me thing strongly that it isn't a spacecraft, though, since it's gonna get cooked with radiation as it passes that region.
 
Jarhyn said:
Really, getting so close to the sun is the real thing that makes me thing strongly that it isn't a spacecraft, though, since it's gonna get cooked with radiation as it passes that region.
Click to expand...

EVERY space-craft launched from Earth is initially closer to the Sun than 3I/ATLAS will ever get. During its "close approach" to Venus, the alien probe is gazing on that goddess from beyond Earth's orbit. (I'd have posted a link to one of the orbit viewers, but I don't even know how to best set parameters.) And as for radiation protection, the alien probe (if that's what it is) is protected by its thick rocky shell.

Were the close approaches to Mars, Jupiter (and to a lesser extent Venus) part of a plan? Why not a close approach to Earth as well, or instead of? Could it be that the aliens are already suspicious of Earth (perhaps due to earlier probes) and deliberately left Earth off their itinerary, hoping to pass by undetected?
 
Isn't earth in quarantine? A pariah planet where the lunatics are kept away from rest of the galaxy because the citizens of civilised worlds would be mortified by human behaviour?
 
The use of probabilities as to ET origins is entirely subjective. The cost of large interstellar probes would be astronomical, get it...hee haw.

I like the Star Gate SG1 huge pyramid spaceships. Roaming the galaxy in luxury and style.

Comets are chemically analyzed using two main methods: remote spectroscopy, which analyzes light from the comet's coma and tail to identify chemical signatures, and in-situ mass spectrometry and sample return missions, where spacecraft use instruments to directly measure or collect samples of gas and dust for analysis on Earth. These techniques reveal a comet's composition, including water, carbon dioxide, organic molecules, and minerals, providing insights into the early solar system and the origins of life.
Click to expand...

| NASA Astrobiology Institute

astrobiology.nasa.gov astrobiology.nasa.gov

en.wikipedia.org

3I/ATLAS - Wikipedia

en.wikipedia.org en.wikipedia.org

3I/ATLAS, also known as C/2025 N1 (ATLAS) and previously as A11pl3Z, is an interstellar comet[1][2] discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) station at Río Hurtado, Chile on 1 July 2025. When it was discovered, it was entering the inner Solar System at a distance of 4.5 AU (670 million km; 420 million mi) from the Sun. The comet follows an unbound, hyperbolic trajectory past the Sun with a very fast hyperbolic excess velocity of 58 km/s (36 mi/s) relative to the Sun.[6][c] 3I/ATLAS will not come closer than 1.8 AU (270 million km; 170 million mi) from Earth, so it poses no threat.[17] It is the third interstellar object confirmed passing through the Solar System, after 1I/ʻOumuamua (discovered in October 2017) and 2I/Borisov (discovered in August 2019),[18] hence the prefix "3I".

3I/ATLAS is an active comet consisting of a solid icy nucleus and a coma, which is a cloud of gas and icy dust escaping from the nucleus. The size of 3I/ATLAS's nucleus is uncertain because its light cannot be separated from that of the coma.[19] The Sun is responsible for the comet's activity because it heats up the comet's nucleus to sublimate its ice into gas, which outgasses and lifts up dust from the comet's surface to form its coma.[20] Images by the Hubble Space Telescope suggest that the diameter of 3I/ATLAS's nucleus is between 0.32 and 5.6 km (0.2 and 3.5 mi), with the most likely diameter being less than 1 km (0.62 mi).[13] Observations by the James Webb Space Telescope have shown that 3I/ATLAS is unusually rich in carbon dioxide and contains a small amount of water ice, water vapor, carbon monoxide, and carbonyl sulfide.[21] Observations by the Very Large Telescope have also shown that 3I/ATLAS is emitting cyanide gas and atomic nickel vapor at concentrations similar to those seen in Solar System comets.[22]

3I/ATLAS will come closest to the Sun on 29 October 2025, at a distance of 1.36 AU (203 million km; 126 million mi) from the Sun, which is between the orbits of Earth and Mars.[11] The comet appears to have originated from the Milky Way's thick disk where older stars reside, which means that the comet could be at least 7 billion years old—older than the Solar System.[23][9]
Click to expand...
 
Swammerdami said:
Jarhyn said:
Really, getting so close to the sun is the real thing that makes me thing strongly that it isn't a spacecraft, though, since it's gonna get cooked with radiation as it passes that region.
Click to expand...

EVERY space-craft launched from Earth is initially closer to the Sun than 3I/ATLAS will ever get. During its "close approach" to Venus, the alien probe is gazing on that goddess from beyond Earth's orbit. (I'd have posted a link to one of the orbit viewers, but I don't even know how to best set parameters.) And as for radiation protection, the alien probe (if that's what it is) is protected by its thick rocky shell.

Were the close approaches to Mars, Jupiter (and to a lesser extent Venus) part of a plan? Why not a close approach to Earth as well, or instead of? Could it be that the aliens are already suspicious of Earth (perhaps due to earlier probes) and deliberately left Earth off their itinerary, hoping to pass by undetected?
Click to expand...
I can only imagine that if you have a probe designed to launch life into a system, the most dangerous places to go with it include "anywhere near the habitable or inhabited world".

The goal wouldn't be research the goal would be "beach-head" and competing over an already contested world is just "not good business" given the potential for life between the two being incompatible or interfering with one another.

Earth is a planet that I would have no desire to be on or near as an ET, at least until I was already established somewhere and difficult to kill at that point.

It's just more stress and likely challenge.

As for costs @steve_bank, it's way cheaper to drill inside a trojan rock and use that for convenient shielding and structure and whatnot, especially if it already has enough velocity to "exit" afterwards.

That way, all you have to do is match course with it with something relatively small. If it contains or will pass through a region of space that WILL contain what you need (or can be redirected once outside a gravity well to do so), then the costs for exploration go way down.

I would put all the places where reasonably advanced life could probably continue to exist, but where it is highly unlikely to start (or where it had failed), on my primary itinerary. This way, whatever life I would need or bring to use to maintain my objectives wouldn't be out-competed by local life that could be toxic to or incompatible with whatever teraforming process I need to maintain my beach-head.
 
steve_bank said:
Rendezvous With Rama

en.wikipedia.org

Rendezvous with Rama - Wikipedia

en.wikipedia.org en.wikipedia.org

Rendezvous with Rama is a 1973 science fiction novel by British writer Arthur C. Clarke. Set in the 2130s, the story involves a 50-by-20-kilometre (31-by-12-mile) cylindrical alien starship that enters the Solar System. The story is told from the point of view of a group of human explorers who intercept the ship in an attempt to unlock its mysteries. The novel won both the Hugo and Nebula awards upon its release, and is regarded as one of the cornerstones in Clarke's bibliography. The concept was later extended with several sequels, written by Clarke and Gentry Lee.
Click to expand...

Looks like it was recently made into a movie.

What dies ET call humans in spaceships? Spam in a can.
Click to expand...
Fantastic books! The movie has been in the works for many years. I hope it does Justis to a great story.
 
Jarhyn said:
It could, but that still means needing to get the thing. I would much rather get as close as possible to a destination before dropping payloads, also potentially because some kind of scans might be on the itinerary.

my goals in a system, if I were to be an alien driving that rock, would be to drop something at a legrange point of a larger outer planet; to fly by the neighborhood of the Goldilocks zone; to fly by the star?

Really, getting so close to the sun is the real thing that makes me thing strongly that it isn't a spacecraft, though, since it's gonna get cooked with radiation as it passes that region.
Click to expand...
It's coming in slow. If it's a created object that implies the creators are subject to reasonable Δv capacity and thus will care about how efficiently any probe reaches it's destination. Thus you eject your probes as far out as you have information to target them with. Venus, Earth, and Mars have atmospheres sufficient for an aerocapture maneuver and that's the best deal going in Δv; and they are close enough to the sun for solar power. Any hypothetical probes were probably ejected as far out as the atmospheres could be analyzed for suitability (there's not a lot of margin on Mars, you need to be sure it's an aerobrake and not a lithobrake) and are coming in dark (as they have no power out there.) Given our track record on seeing asteroids we very well might not detect it until it begins it's aerocapture.
 
If all those ETs, us included, are sending out probes interstellar space must be filled with space junk.

Hazards to space navigation.

Five NASA spacecraft have achieved interstellar trajectories, and as of 2024, Voyager 1 and Voyager 2 are the only two that have officially entered interstellar space by crossing the heliopause. The other three, Pioneer 10, Pioneer 11, and New Horizons, are also on paths out of the Solar System, though contact with the Pioneer probes was lost before they reached interstellar space.
Click to expand...
 
steve_bank said:
If all those ETs, us included, are sending out probes interstellar space must be filled with space junk.
Click to expand...
How bad can it get if it's all confined to this one little galaxy? The real bad news is when we start polluting intergalactic space!
 
The first issue for an uninhabited probe is energy.

The next is navigation. Navigation from one star to another specific star. Relativity apples, you see it where it was not where it is. I do not see a practical navigation system to do that. You can't get the accuracy needed of yours and the target's changing positions.

The odds of an ET probe showing up in or solar system is remote.

Unless of course ET has science well beyond ours. But ten ET would end up orbit saying they come in peace....
 
Still far too slow for practical interstellar travel. Thousands of years of travel time between stars would be playing an incredibly long game.....
 
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