And why would it be? It was HUGE. Why on earth would aliens design a probe so large? It would take a ton of energy to make it to our solar system (like, a star exploding... hmmm..).

If aliens have probed us, I DOUBT we would have actually noticed them. Because, likely the probe would be about the size of one of our satellites and maybe even a lot smaller to cut down on the amount of energy needed to get them here.

You're making a lot of assumptions here and basing it on the limited knowledge of a specifies that has failed to make any significant strides into exploring anything other than its own solar system.

There's an easy answer that coincides with our current understanding of physics. Then there is "Aliens have discovered tech that makes it easier for them to fling a half mile long object vs a satellite sized object across the stars at a relatively slow speed."

Sorry if I take "explosion makes rock go far" as being the more plausible explanation than "Aliens want to wait a million years for a brief glimpse at a distant solar system".

It's not the size/volume that matters, but the mass. Even with our limited science and technology, we have designs for interplanetary ships that drag hundreds of meters of radiator surface with them. It's not hard to imagine - and it has been imagined many times - a ship that consists of a core with a gigawatt-range powerplant, reaction mass, efficient engines, and kilometer-long radiators to dump the powerplant heat into space. If anything, based on our knowledge and assuming no magitech breakthroughs in space propulsion, you should expect interstellar ships to be large but light, maximizing surface area while minimizing mass.

To be fair, there is no need for the probe to have been designed for a mission to our star system. It could be that it was a craft meant for something else entirely that left its star system, like our Voyager probes have, and drifted for eons before happening to pass through our star system and be observed.

Of course, that is still less likely than some unusual rock doing the same thing.

Sure, just a bunch of energy for such a large object. "To see if they can" may very well be a reason, but that doesn't seem likely for a species that advances far enough to be able to accomplish such an achievement.

> Sorry if I take "explosion makes rock go far" as being the more plausible explanation than "Aliens want to wait a million years for a brief glimpse at a distant solar system".

Playing Devil's advocate, a probe that size would likely visit many star systems, the Solar being a random one in the bunch. The brief pass would be necessary to avoid the energy expenditure of braking and reaccelerating.

"You don't know everything therefore aliens" is my favorite argument too

I don't think this was an alien probe but the size argument is not convincing to me. I would think that if you want to design a probe that can keep going for very long time spans and distances it would have to be big and work more like a factory that can constantly refresh its parts. Devices of the size of our satellites aren't and probably can't be designed to last thousands or millions of years. Something bigger on the other hand can be designed that way.

The object was actually in the rest frame of our local patch of the galaxy, so in essence, we came to it via our motion about the center of the galaxy.

Size is so relative. You're thinking in human scale. Who says all life in the universe is the same size as us?

All life in the universe faces the same kinetic energy equations to cross the stars.

And if the stars are the equivalent of our atoms to a much larger form of life, what would it's nanotech look like to us?

Probably not the same energy availability, though.

The specific reason he contends it may be an alien artifact is that he believes its characteristics match the profile of a light sail:

1) its shape may actually be more like a pancake than a cigar, a crumpled light sail would match this 2) it showed unexpected acceleration away from the Sun without outgassing. 3) its velocity is very close to the mean motion of our local stellar neighborhood, if you needed to drop a solar sail after deceleration so that it would be hard to work out what system you came from then this would be the velocity to do it at.

A size 1000m x 150m seems pretty small for something that would have taken tens of thousands of years to get to our system.

I think one theory is that it’s a huge “light sail” (hence the size). Just what I heard; no idea if this has any merit.

> Out of my network of ~200 astronomers/physicists, I haven't heard one person support the idea that this is an alien probe.

I've heard little to nothing in any media articles of anyone supporting alternatives.

Is it once a year these are thought to come through, or 100 times a year? Do we get things that are 100 times smaller at 100 times the rate?

If people won't make a public call, then lets run with aliens.

I was a fan of it's not interstellar, just more fake 'life on Venus' science, but reading some journal articles[1], it seems like it is expected. But it's been hard to work that out.

[1] Realistic Detectability of Close Interstellar Comets https://iopscience.iop.org/article/10.3847/0004-637X/825/1/5...

Can it be proven that it is not an alien probe?

Can it be proven that there's not a teapot in the asteroid belt?

Extraordinary claims required extraordinary evidence. A massive rock being hurled to by a supernova to our solar system is far more likely than advanced aliens dumping a ton of future tech to get this huge thing into our solar system for a split second.

Why? Because, it would cost a lot of energy, something I doubt an advanced race would spend. Further, an advanced race that wants to probe us wouldn't need such a huge object, it's far easier to observe from a far (think, james webb telescope but better). Sure, hard to know what aliens are thinking, but it just seems incredibly unlikely they are thinking "Let's build this half mile long space probe for a glimpse of a distant solar system and send it off for a million year journey".

A star exploding and sending a bunch of mass our direction is far more likely. Why? because we know that happens relatively frequently.

> it would cost a lot of energy, something I doubt an advanced race would spend.

While I agree with your overall conclusion, I don't see that we have any evidence that as a race progresses technologically, they spend less energy. The opposite seems to be true.

Russell's teapot: https://en.wikipedia.org/wiki/Russell%27s_teapot

I can't prove it's not an alien probe, no. But I can't prove it's a piece of space debris that just wandered through, either, so why not assume that too?

The problem with "can't disprove" being used as evidence is that you need to consider the full universe of statements that we "can't disprove", but humans tend to think as if "alien probe" is a privileged statement simply because it is cognitively appealing and drives our imagination. If you put it on a list of the things we can't disprove about this particular object, it wouldn't really be the most likely one you'd find.

On the flip side, you also ought to consider the question of all the objects for which we can't disprove they are alien probes. It isn't just this particular object; the solar system is filled with millions of objects we can't disprove are alien space probes, things we've labelled as "asteroids" based on a streak someone took a picture of once. Apply the same standard to all of them that is applied to this object; does it now claim that the solar system is just filled to the brim with alien space probes? Probably not good logic.

Personally, I can't wait until we improve our detection a bit and detect another several dozen things like this object so we can get over this and real science stories can be written about these objects again. Guess this is a taste of what reading about pulsars must have been in the first few years.

I can't prove you're not an alien infiltrator either, but I'm not about to write a book about it.

> I can't prove

This is a good reason enough for some people to write a book for a general audience!

I'm god. God is now writing to you: Please send all your earthy valueables (money, bitcoin, house paper, car keys etc.) to me.

Thanks!

I get this kind of request in my email once in a while... There's too many of You.

We are all right :D

The only earthy valuables I own are some potted plants, and some mushrooms in the refrigerator.

Will that do? I also have some whole wheat bread that my kids say taste like dirt.

My point is, have you read the book and can you specifically point to why his theory is wrong? I'm not saying he is right, but I think if you are going to cut him down, be specific about why he is wrong.

Can you prove I'm not God?

There are no gods (not on HN anyway).