Rapid Brightening of 3I/Atlas Ahead of Perihelion | Hacker News Reader

Rapid Brightening of 3I/Atlas Ahead of Perihelion

arxiv.org

31 pointsbikenaga78 comments

One of my (highly educated and successful) buddies thinks it some sort of alien interstellar probe. I told my 13 year, who keeps up with these kinds of things, and asked what he thinks. He just kind of stared at me and then said "i think it's a comet from outside the solar system." and went back to playing DCS. heh from the mouth of babes..

Clearly your son has not studied its orbital path near 2 major planets.

What in said path would you like to highlight?

https://commons.wikimedia.org/wiki/File:ESA%E2%80%99s_Mars_a...

https://en.wikipedia.org/wiki/3I/ATLAS#Trajectory

It goes very close to 2 major planets. What's the chance of that?

It was only detected when 4.5 AUs from the Sun (which, I'll also note, exerts significant graviational force on inbound objects). It was already close; we can't currently detect the tens/hundreds/thousands of similar objects likely whizzing past at further distances as we speak.

If it was 100 AUs at closest approach, we would never have seen it. (https://en.wikipedia.org/wiki/Oort_cloud is still theoretical, even)

The chances of yesterday's Powerball numbers being 04 24 49 60 65 01 was about 1:300M.

I don't think you understand what I'm talking about. Look at how close it goes to Mars and Jupiter.

> Look at how close it goes to Mars and Jupiter.

You're doing the thing. https://commons.wikimedia.org/wiki/File:Survivorship-bias.sv...

It's close because we saw it. We saw it because it's close.

We are not on Mars or Jupiter.

We are (via our robot representatives). In fact, they're our closest vantage points to this thing.

https://www.esa.int/Science_Exploration/Space_Science/ESA_s_...

This thing traveled light years to get here. Possibly over billions of years. 30 million kilometers from Mars and 300 million and 3 billion kilometers from Mars would all be close approaches. Any approach can be claimed to be close; that's the magic trick at play here.

Our robot representatives there were not the ones who spotted it, so what relevance is it that they are there?

I don't think you're responding to my claim, which is that the close passes to Mars and Jupiter seem very unlikely. Of all random trajectories through the solar system at the distance of this body, what fraction of them pass equally close to major planets? I'd even be willing to limit it to trajectories close to the ecliptic plane, because we may be scanning that plane more.

I am responding to your claim.

4.5AUs is as close as 0.2AUs from an interstellar standpoint. Both are equally likely, just as every Powerball number is equally likely. Any object of this nature we can spot is going to be quite close with our current detection technology.

Again, your argument is effectively like arguing that 04 24 49 60 65 01 cannot possibly be yesterday's winning Powerball numbers, because it's a 1:300M chance. The game must be rigged!

Now, if the next couple interstellar objects we detect also do a similarly close pass on Jupiter and Mars, there'll be something worth wondering about.

(Similarly, if tomorrow's Powerball numbers are 04 24 49 60 65 02, I'll have questions!)

You are basically saying that if the first Powerball number drawn was 01 02 03 04 05 06 that there would be no reason to suspect something wrong with the Powerball lottery process. It's random! It could happen!

Yes I understand that random trajectories could potentially be anything. But it's notable that this particular random trajectory has an unusual characteristic. It's a characteristic that an alien probe might have. That's what makes it interesting.

Yes. People hate this fact, because it feels very counter-intuitive, but 01 02 03 04 05 06 and 04 24 49 60 65 01 are equally likely.

You need more than one data point to determine if something screwy is happening. (And, again, the available set of interstellar objects is both very small (n=3) and incredibly biased towards very close ones.)

Your first statement is correct, but your second doesn't follow and is incorrect.

If the first numbers that comes out of the Powerball lottery are 01 02 03 04 05 06, then we don't need another one to state that something screwy is very likely to be happening.

You may feel that way, but it's not true statistically.

(Barring other evidence. If Bob from Powerball IT wins that first drawing with those numbers, for example.)

If I saw the numbers "01 02 03 04 05 06" from code that's supposed to spit out random numbers, my first thought won't be "well, statistically that's just as likely as any another 6 numbers". My first thought will be, did someone set random=false?

Sure. We also hear a creak at night and think it’s a ghost. Or we rage when our sniper with 99% odds misses in XCOM. Humans are like that.

This isn’t even that sort of case. The closest approach is something like 30M kilometers.

What sort of case is it then? Isn't your argument that we can't distinguish any "sort of case" at all?

We need a larger sample size than n=3 and better surveillance of the solar system. What’s weird for in-system objects may be the norm for interstellar ones. Astronomy is a constant barrage of “huh, wtf is that?” without aliens being the explanation.

Someone really aught to add a picture at the bottom of this article with a gif of aliens saying "take me to your leader"...

Anybody else feel like there're just ... too many active plotlines?

It is/isn't the Singularity while we are going and not going into WW III, while Rama is maybe zooming by, while Modern Rome does the whole fall of the Republic nonsense, or maybe doesn't! While the H5N1 thing is still churning away reassorting in pigs!

Narrative superposition is exhausting.

Turn off active screen devices and go for a (very long) walk. News are exhausting only if you allow them to be.

I appreciate what you're trying to say here, but this was more an infovore glorying in how weird everything is than someone who has too much screen time (I don't, in fact, even use a screen.)

But also sometimes monitoring the world is useful. I'm very glad I was paying attention in February 2020, for instance!

>(I don't, in fact, even use a screen.)

I don't understand. How did you write this comment?

Click their username.

> I'm a totally blind software developer.

Don't forget a bunch of infected rhesus monkeys escaping an overturned truck.

ffs. Seriously?

https://www.nytimes.com/2025/10/29/us/monkeys-euthanized-mis...

Not infected. Maybe the story updated after you first read it.

One small thing we can all calm down about. =)

oh my science! it's just like in Ant Man 3 on iMax

Just a heads up that you likely shifted into a parallel universe.. iMax doesn't exist; we have HBO Max

Welcome! I certainly hope this universe is better than your original one

How cool is it that, as a species, we developed tools to allow us to continue watching an interstellar object zapping the void on the other side of the sun!!!

Seeing how everything is going, though, I strongly feel like we peaked as a species and that, while we'll continue up for a (short) while, the downgrade is just inevitable.

To be clear, we're not looking through the Sun at the object. We're looking past the Sun at the object through a telescope that is positioned to observe the Sun, for the most recent imagery.

I agree with you, but I have been experimenting with image processing using the data available from this satellite (as a hobbyist). Honestly, while it's impressive that we gather data from a piece of technology that's floating in space, the resolution of this is nothing to write home about. If I take anything away from my brief amount of experience with this, it's that we still have a long way to go in terms of the quality of our imaging of our surrounding space.

I haven't fully finished my processing yet and still need to tune the wavelength and account for some drift, but this is basically the state-of-the-art: https://tcdent-pub.s3.us-west-2.amazonaws.com/3i_atlas_10302...

slightly off-topic thought experiment that's been on my mind lately:

to us, the sun appears to be the size of, let's say, a quarter held at arm's length. this is at 93M miles (1AU, or ~8 light minutes) distance. if we moved the sun 100 miles away from earth, it would take up the entire sky. now in the other direction, if we doubled the distance, to 2AU, it would appear to us as half its normal size and 1/4 as bright (irradiance follows inverse square law). at 3AU the sun would be 1/9 as bright and 3x smaller than a quarter. at 100AU, we're talking about brightness of 1/100^2 (one ten-thousandth) the sun's apparent brightness. with me so far?

Sirius A: the brightest star we can see; 25x more luminous than the sun; 2x the size of the sun; 8.6 light YEARS distance (544,000AU) from earth.

if we moved the sun to the same distance as Sirius A, it would appear 296 BILLION times dimmer and 544,000 times smaller. yet Sirius A is easily visible - the brightest star in our sky - despite being only 25x more luminous and 2x larger.

do you see the discrepancy? 25x more luminous doesn't compensate for a 296-billion-fold brightness loss. The numbers we are given don't make sense, not even close. (and this is without considering diffusion, which would make the discrepancy even worse.) i'm not proposing an explanation or a modification to the model, i just think the data don't make sense.

>The numbers we are given don't make sense

These are all numbers you just provided, with no source for them.

But even using your numbers, 300 billion is 3x10^11. The Sun provides about 10^5 lux, while starlight overall provides about 10^-4 lux[1], which is a difference of 10^9, meaning the difference between "all the starlight on a dark night" and "just the starlight from Sirius" would be around 10^2, which... seems about right?

1. https://en.wikipedia.org/wiki/Orders_of_magnitude_%28illumin...

Yeah, people get really messed up by just how good our eyes are. (For a close-to-home example, people think indoor plants get a lot closer to sunlight-level amounts than they really do.)

We can spot a single photon in the right conditions. https://www.nature.com/articles/ncomms12172

Eye sensitivity isn't the issue. Sirius isn't barely visible at the detection threshold, it's the brightest star in our sky. If a 25x luminosity boost over the Sun only gets you to the edge of naked-eye visibility at that distance, where do the additional orders of magnitude come from to make it one of the most prominent objects in the night sky? Show me the math.

> Sirius isn't barely visible at the detection threshold, it's the brightest star in our sky.

And it's entirely washed out during the day. The full Moon is very bright, but it's still 400,000 times dimmer than the Sun when seen from Earth, and that's only ten different. The brightest star in our sky is simply not very bright; our eyes are just pretty awesome.

That star you are seeing is 25 orders of magnitude dimmer.

https://astro.wku.edu/labs/m100/mags.html

"While you may perceive one star to be only a few times brighter than another, the intensity of the two stars may differ by orders of magnitude. (Light intensity is defined as the amount of light energy striking each square cm of surface per second.) The eye is a logarithmic detector. While the eye is perceiving linear steps in brightness, the light intensity is changing by multiplicative factors. This is fortunate; if the eye responded linearly instead of logarithmically to light intensity, you would be able to distinguish objects in bright sunlight, but would be nearly blind in the shade! If logarithms are a faint memory, you should peruse a refresher on logs and logarithmic scales before continuing."

https://physics.stackexchange.com/questions/329971/how-many-... says looking up at a sunny sky lets you take in 3×10^14 photons per second per eye. Yet you can see a single photon! https://www.nature.com/articles/ncomms12172

Or, we can conclude the entire field in dozens of countries simply can't do math. Your choice.

Look up the provided numbers if you disagree.

You're comparing the Sun's illuminance at Earth (10^5 lux at 1 AU) to all starlight combined (10^-4 lux), then trying to work backward to what a single star should provide. That's not how this works.

The question isn't "what's the ratio between sunlight and all starlight." The question is: what happens when you move the Sun to stellar distances using inverse square law?

At 1 AU: ~10^5 lux

At 544,000 AU: 10^5 / (544,000)^2 = 10^5 / 3×10^11 ≈ 3×10^-7 lux

That's the Sun at Sirius's distance. Multiply by 25 for Sirius's actual luminosity: ~7.5×10^-6 lux.

Your own Wikipedia source says the faintest stars visible to naked eye are around 10^-5 to 10^-4 lux. So we're borderline at best, and that's with the 25× boost.

But moreover, you said "the difference between all starlight and just Sirius would be around 10^2." There are ~5,000-9,000 stars visible to the naked eye. If Sirius provides 1/100th of all visible starlight, and there are thousands of other stars, the math doesn't work. You can't have one star be 1% of the total while thousands of others make up the rest - unless most stars are providing almost nothing, which contradicts the "slightly brighter" compensation model.

Address the core issue: inverse square law predicts invisibility. The 25× luminosity factor is insufficient compensation. Citing aggregate starlight illuminance doesn't resolve this.

It's been a long time since my astrophysics, but I think the seeming contradiction you're running into might be from treating lux (illuminance) as a measure of emitted energy, when its actually a measure of received energy.

The Sun's (or any star's) emitted energy is measured in terms of solar luminosity.[1] The nominal value of solar luminosity is 3.83×10^26 watts. At twenty five times as luminous, Sirus' luminosity is 9.5710^27 watts. We can divide that by your 296 billon times, which gives.. 3.2x10^16 watts as what actually makes it to Earth. If the we convert that back into solar luminosity (to figure out the apparent brightness at Earth), its 8.3595 10^-11.

Now, if we look up at the sky, and check how bright the Sun and Sirius are from Earth on the magnitude scale, which each step is ~2.5 times brighter than the one below it (and vice versa), the Sun has an apparent magnitude of -27, while Sirus' is -1.46. I.e. the Sun in the sky is about 8 billion times brighter that Sirus is. That's within an order of magnitude of what its calculated solar luminosity should be. Again, it seems about right.

1. https://en.wikipedia.org/wiki/Solar_luminosity

I've found that when I have a thought that seems to contradict the "established" model of the world, I tend to just be missing some critical factor. A recent example is when I thought: "why don't we just use physical objects to communicate information? Wouldn't that be instantaneous?" Turns out, no, pushing on one end of an object only communicates information to the other end at the speed of sound. Not intuitive when you only think about observable experience (it sure seems like if I push a steel bar, the other end moves instantly), but that's how the world works.

In the case of your thought experiment, the critical factor is that our eyes are able to observe and adjust to a very wide range of brightness in different conditions. Sirius A really is billions of times dimmer than the sun to our eyes (hard to find a good reference for that, but this mentions it: https://ecampus.matc.edu/mihalj/astronomy/test5/stellar_magn...).

Your steel bar example isn't analogous. You had an intuition, discovered a physical constraint (speed of sound), and the math checked out. The constraint explained the phenomenon. What would it look like if the "established" model of the world were actually wrong?

Here, the math doesn't check out. That's my point.

I'm not saying "it seems like stars should be invisible but they're not", Im showing that inverse square law - which we can verify at human scales - predicts invisibility at stellar distances, and the proposed compensation (25x more luminosity) is insufficient by orders of magnitude.

Sirius is "billions of times dimmer" than the sun to our eyes IF you mean the Sun as seen from Earth versus Sirius as seen from Earth. But that's not the comparison. The comparison is:

Sun moved to 544,000 AU (Sirius's distance): 296 billion times dimmer than Sun at 1 AU Sirius at 544,000 AU: 25x brighter than that

25x doesn't bridge a 296-billion-fold gap, plus the eye's dynamic range is irrelevant; we're comparing what brightness should reach the eye versus what compensation the model claims.

If your claim is "the eye can see across many orders of magnitude, so even though the Sun would be invisible at stellar distances, Sirius being slightly brighter makes it visible," then do the actual calculation. Show that 25x more luminosity produces enough photons to cross the detection threshold. Because the math I'm showing says it doesn't.

You're assuming the model works and looking for why my intuition is wrong. I'm showing the model's numbers are internally inconsistent. Those aren't the same thing.

>I've found that when I have a thought that seems to contradict the "established" model of the world, I tend to just be missing some critical factor.

Does it bother you that to make relativity work, they had to invent dark matter and dark energy - 96% of the universe's mass-energy - as fudge factors? At what point does "missing a critical factor" become "the model requires constant patching to match observations"?

> Does it bother you that to make relativity work, they had to invent dark matter and dark energy - 96% of the universe's mass-energy - as fudge factors? At what point does "missing a critical factor" become "the model requires constant patching to match observations"?

This would be a lot more compelling from someone who doesn't believe in astrology.

https://news.ycombinator.com/item?id=45631792

(It's interesting that you forget the inverse square law in that case.)

I think I see what you mean now, but what makes you think that the sun would be invisible at 544,000 AU?

Here are the numbers as far as I understand them.

Apparent magnitude of the sun: -26.74 Apparent magnitude of Sirius A: -1.46

Excepted magnitude of the sun after moving to 544,000 AU: 296 billion times weaker, leading to +1.96 magnitude, according to a calculator (https://www.1728.org/magntude.htm).

I don't trust that calculator a lot, so to check that math, I used a formula to calculate the difference between those magnitudes (https://lco.global/spacebook/distance/comparing-magnitudes-d...) and got a result of 23.34. Not far off from the expected 25x difference.

So the sun at 544,000 AU wouldn't make the top 25 brightest stars in the night sky, but it wouldn't be far from that (https://www.britannica.com/science/list-of-brightest-stars-2...) and definitely well within what would be visible (https://en.wikipedia.org/wiki/Limiting_magnitude).

For those unaware, there are a ton of AI generated videos across YouTube, TikTok, Instagram, Facebook of physicist Brian Cox saying this is an alien spacecraft:

https://www.ign.com/articles/physicist-brian-cox-thanks-yout...

Damn interstellar tourists, just coming here, taking in the sights and leaving. The least they could do is spend some money in the local economy, smh.

Don't worry, Avi Loeb is on it. https://avi-loeb.medium.com/3i-atlas-rapidly-brightens-and-g...

"Does it employ a power source that is hotter than the Sun?"

Sigh.

I don't like to discourage questions like that, because they kill curiosity. We know what the likely answer is, but reasonable assumptions are just that. Assumptions. Why not let mind wander about the exciting ( if somewhat hard to consider as possible ) lines of thinking.

There's a difference in asking questions and pushing as fact with no evidence. It swings both ways

Plus he is an authority figure with a captive audience. He has a much higher responsibility than the average person speculating.

Yeah it doesn't instill a lot of confidence in the quality of ivy league credentials when guys like this are running around spouting nonsense. I'm surprised there's not a clause in his employee handbook that says to not be an obvious troll. Kooky science is one thing but this is just the type of person the men with butterfly nets and white coats should be interested

Huh? What is Loeb's 'captive audience'?

UFO nuts desperate for anyone with a shred of academic credibility.

What is Loeb pushing as fact with no evidence? Can you provide a representative quote?

You can easily answer this with a Google search.

No, I can't, because all I've seen from Loeb is pretty clear about what is fact, and what is speculation.

I don't know, and there's no way to find via "Google search", what HN user ~dylan604 is specifically alleging has been improperly "pushed as fact".

If it's clear to you, can you share a representative quote from Loeb? He's got a lot of writing to choose from!

[flagged]

He moved from merely asking questions to promoting an unsupported claim without any real evidence (repeatedly). he's not curious.

Planetary scientist academics are angry because he's getting all of the attention and it isn't even in the field he's most known for previously. Even smart humans are still humans.

Maybe it's being driven by Bat Boy?

I miss the days when tabloid fodder stayed in the tabloids.

That's a pretty wild, and public, hypothetical for someone with his standing at Harvard.

That's his grift these days.

He'll have the same to say about the next one.

When we observe a fourth interstellar object, I'll gladly read Avi Loeb's wildest speculations alongside more measured perspectives. This is the third time we're observing an interstellar object?

Yes, this is the third to be spotted.

1. https://en.wikipedia.org/wiki/1I/%CA%BBOumuamua

2. https://en.wikipedia.org/wiki/2I/Borisov

3. https://en.wikipedia.org/wiki/3I/ATLAS

2/3 of them Loeb has made wild claims about.

Why would someone "with his standing at Harvard" be expected to avoid "wild, and public, hypothetical[s]"?

Does everyone at any prestigious institution have some duty to remain conventionally mundane in all their musings?

Is there any reason to think such hypotheticals are, on net, more harmful than helpful?

Isn't tenure (like Loeb's) designed to encourage a fearlessness around topics & speech?

Wouldn't be especially interesting if it did. Even a mantis shrimp can do that: https://old.reddit.com/r/interestingasfuck/comments/og0n3b/t...

It would be deeply interesting for a comet to have a power source of any kind.

A volcanic comet?

A (hot) volcano on a comet would be very interesting, especially if said volcano was hotter than the sun.

Even with cryovolcanoes, the power source is not on the comet; it's the sun.

Maybe it's a chunk of https://en.wikipedia.org/wiki/Przybylski%27s_Star -- which admittedly is pretty darned strange in itself.

This doesn't mean everyone is overhyping the comet, it means you're underhyping the mantis shrimp. There are a number of absolutely unimaginable miracles of nature on Earth.

Fewer every year. If 3I/A is ET flyby, perhaps our progress trading primitive simulacra for biological miracles will satisfy it that we pose no great risk, annihilation being costly and reserved for planets with better long term odds

How do you figure? Just because we gain some understanding of how a caterpillar turns to slush, then turns into a butterfly, yet somehow retains some level of memory from before, doesn't mean that it's somehow less of a miracle.

Strongly agree. Our beginning to grasp how it works even adds to the miracle!

But what we're beginning to understand we're also destroying far more rapidly even as we devote more and more effort to digital facsimiles of our faculties

My dry pessimism was a comment on this foolish inversion of priorities. Alien visitors, if the forest is truly dark, may conclude we're well on the way to self-annihilation in pursuit of false idols, while we fail to recognize the miraculous nature of existing biology.

Sure, I can agree. We probably need to spend more time focused on Earth. There are many mysteries still.

Yes, so many.

Dr. Avi has a pretty clear point and he goes into details on the JRE released just yesterday. https://youtu.be/EaAun27gftk

What most stand out is the sheer amount of closed mind people in the accademia, Avi is not afraid of making suggestions of what it might be and even saying “if it turns out of being a rock, so be it”.

Just to be clear, "here he is shilling it to Joe Rogan" was intended to support his theory?

> even saying “if it turns out of being a rock, so be it”

I don't doubt it! He'll get another chance the next time we spot another one.

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