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Comment by sjclemmy | Hacker News Reader

I'm still convinced this is an alien probe. I mean look at that trajectory. 0.163 AU from Earth - what are the odds? The spinning is irrelevant surely - I mean, it's all relative, so as far as ’Oumuamua is concerned, we're spinning. Maybe it was spinning that way to stay aligned with a distant companion for communication.

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I prefer a complementary theory -- that it's a spent stage of a multi-stage spacecraft. If the primary stage were decelerating for a rendezvous with Earth, then any stage that made it to full acceleration would reach us first, probably getting close and then flinging back out of the solar system, just like this did.

Easy enough to test -- we'll eventually see another object following the same trajectory, give or take, but that's decelerating.

(Cue the dramatic music.)

"And on far-off Earth, Dr. Carlisle Perera had as yet told no one how he had wakened from a restless sleep with the message from his subconscious still echoing in his brain: The Ramans do everything in threes."

Great series of books! Every time I see a thread about this big rock I think of Rama.

Beg to differ. Great book. Awful cheap hacks posing as sequels. I regret reading them - they've nearly ruined the original for me.

The final reveal was mind-numbingly bad.

My personal theory is that Clarke's writing partners sedated and tied him inside a closet until the book was finished.

That's the only way to explain how awful some of his last books were.

Having said that, I liked Richter 10. Too bad the co-author died before they could write another one.

My heuristic is that anything co-written by Gentry Lee is not worth my time.

I even wonder why they insisted on it so much.

IIRC, the only reason the sequels exist is that fans (or maybe his editors) pointed out out that if the Ramans "do everything in threes" then there needed to be two more parts to the story. It was never planned as such, though.

I agree with you, they were pretty awful and lost so much of the original's sense of wonder and incomprehension.

One favourite daydream of mine is to think about how the Rama aliens' second and third probes would be received. I read Rama around the same time as Eon by Greg Bear, so I've always had an affinity for spin-gravity habitats filled with unknown stuff :)

With The Expanse TV series showing us how good hard scifi can be exciting and wonderful, I'm hoping we one day get an Eon or Rama series. Rama especially would work well in a hard scifi miniseries format.

(That's actually a great thought: that many shows thought impossible a couple of decades ago will now be made. Let's just hope they're made with love and devotion like The Expanse!)

For anyone curious as I was, this is a quote from "Rendezvous with Rama" by Arthur C. Clarke.

https://www.wikiwand.com/en/Rendezvous_with_Rama

What if the object was already traveling in our rough direction and aliens decided to simply take advantage of the free ride? They tweaked the direction with a few thrusters to pass by Earth, and they left the rotation to help camouflage the object with its natural tumble through space. Finally, they deboarded the object when they reached their desired location nearest to Earth.

It's fun to speculate, but I'm sure the reality of the situation is far more boring.

Maybe it was intended to be a booby trap for the Zentraedi?

Looking at the images on that site, the trajectory doing a "fly by" of a lot of the planets did look remarkedly like the sort of thing we've being doing for decades in our own solar system [1]- line up a bunch of planets and use gravity slingshots to do a close fly-by to get a closer look.

The thought makes me have goose-bumps. Did some alient race just take a close look at us? Was there a voyager-style plaque on it? I guess we'll never know now.

Occam tells us that in reality it is most likely just some space debris from some ancient rock-smashing incident, but the fact that this thing continues to defy classification allows us some space to imagine!

1 - https://duckduckgo.com/?q=voyager+gravity+slingshot+diagram&...

I wonder if it's speed increased on it's way out. Maybe it's on a multi-system route, using gravity assist as it goes to cut the route time down by a few thousand years here or there as it circles back around to it's home system. Must be very patient aliens, assuming no FTL messaging tech.

> 0.163 AU from Earth - what are the odds?

Look at it from a sampling bias perspective. The object at its brightest was very dim (19th magnitude) and moving fast. The ability for rapid, repeating full sky surveys is recent (PanSTARRS had been online for around a decade). The limiting magnitude of PanSTARRS is 24th. So if such other such objects exist, of course we are going to find the closest ones first since they are the brightest.

> The spinning is irrelevant surely - I mean it’s all relative

That is incorrect. All motion is not relative, only intertial motion is relative. Spinning implies acceleration on a body which is measurably different from any reference frame compared to a body that is not accelerating

What I meant was, the origin of the object may have been in a different inertial frame of reference to our solar system, so the 'spin' as far as it is concerned is not spin.

This is not a thing though. Spin is spin, regardless of reference.

I really misunderstand my relativity then.

You seem to know that the rules of physics should hold in any inertial (i.e. non-accelerating) reference frame. But the thing you missed is that a spinning reference frame cannot be inertial. There is centripetal acceleration when something spins.

You've got the right general idea, but the principle of relativity only applies to constant velocity motion. If two astronauts float past each other in space, either of them can claim that they're motionless and the other is moving past them. However, if one of them is accelerating or spinning, they'll both agree on who it is.

https://en.wikipedia.org/wiki/Principle_of_relativity

https://en.wikipedia.org/wiki/Inertial_frame_of_reference

To add on to this, here's a simple thought experiment to explain why spinning is different from constant velocity:

Imagine you're off somewhere space. You're holding a ball in each hand.

1. You're motionless with reference to the Earth. You let go of the balls. They stay put.

2. You're moving away from the earth with a constant velocity. You let go of the balls. They continue to move at the same velocity as you do: This is indistinguishable from case 1.

3. You're accelerating away from the Earth (using rocket boots). You let go of the balls. They do not continue to accelerate with you.

4. You're motionless with respect to Earth, except that you're spinning. Think of the fastest you've ever spun. You'll be really dizzy when you stop. You let go of the balls. They fly off into space, because in order to stay spinning, they need acceleration toward the center of the spin plane. By letting them go, you stop that acceleration, and their trajectory changes (or really, their trajectory change stops).

Velocity is all relative, but acceleration is not. Spinning is acceleration.

---

Here's another example:

You occupy a cosmos consisting only of you and an apple. You accelerate away from the apple for a moment, then stop accelerating. You now have a constant velocity away from the apple, but it's meaningless to say which of you is actually moving. You each perceive the other as moving away at constant velocity.

Now imagine you start spinning. You feel like you're spinning, and visually, you perceive the apple orbiting you at a bizarrely fast rate. From the apple's perspective, you are spinning. These two perceptions are not symmetric.

I’m really interested in understanding this. So please indulge me... So, I’m Oumuamua rocking my way through interstellar space. I see nothing around me so as far as I know I’m not spinning. Then, all of a sudden I happen upon a solar system that is spinning around me. Who is spinning? Me or the solar system?

Is the point here that I’m spinning with reference to my direction of motion?

Yes. You are aware that you are spinning even without external reference because your outer parts are accelerating toward your inner parts. This is the feeling of spinning in a circle on earth too.

This is how plausible simulated gravity works too. A ship spins. It doesn’t require a reference to know whether it’s spinning.

If one were so inclined, they could argue that the spinning is in fact very relevant, as it would allow a static camera or other observation device a full 360° view along all axes.

Any civilization capable of building an interstellar craft would certainly have mastered the ability to move a camera by then ;-)

Stealth. If you wanted to reveal yourself, you wouldn't need to disguise your probe as space debris.

This has always fascinated me. We can actually build giant spaceships (space stations) inside asteroids and use them for interstellar travel. All the resources we need, including ice would be at our disposal. Like traveling with your own mini-planet.

Dirk Schulze had taken that as a subject into his sci-fiction book - Alien Encounter.

For the book, the reviews on Goodreads aren't very good :-/

https://www.goodreads.com/book/show/18268008-alien-encounter

That's true, but I personally found it pretty engaging. In fact, I read the last 150+ pages in one night. I'd give it at least 4 stars.

From an energy perspective, it's likely better to build your own station (from an asteroid - or alternative, remove all the mass from the asteroid that you don't need) - that way, you're only accelerating exactly the mass that you need, not wasting any energy accelerating the rest of an asteroid.

I think he is talking about chilling on the asteroid while it follows its known trajectory undisturbed, simply because they are packed with useful resources we can gobble up while waiting.

Asteroid are per definition not interstellar though (until Oumuamua?).

An interesting approach would be to send an automated ship builder robot fleet to dismantle an asteroid and board the fully furnished ship when it makes another close approach, and then boosting it to its final destination.

I'd love to see a scenario where we'd build robot terraforming fleets that'd land on an uninhabited planet, make it habitable, complete with spaceports, cities, factories, crops (all permanently tended for robots), build a couple extra fleets and launch to their next most promising targets.

And then, for some reason, humans lose interest in all that and someone else wakes up to find a universe full of 60's futuristic utopian planets nobody ever lived in.

someone else wakes up to find a universe full of 60's futuristic utopian planets nobody ever lived in

Reminds me of the paperclips game [1]. Would be horrid to find those people wake up and find the universe transformed into nothing but paperclips. [1]

[1] http://www.decisionproblem.com/paperclips/index2.html

If it's a space station, then accelerating it is less of a concern than keeping it livable, and a huge amount of matter surrounding you goes a long way to protect you from things that would otherwise kill you.

Now for a space ship, I agree. Though even then you might benefit from that extra matter in the same way.

They’d make great protection from high speed space debris.

This is explored in Seveneves by Neal Stephenson.

You'd still be better off by restructuring all the mass of the asteroid around your spaceship instead of building your ship inside the asteroid.

Also mentionned in Legend of Galactic Heroes by Yoshiki Tanaka. The founder of the Free Planet Alliances escape from its prison world by using ice asteroids as vessels for interstellar travel.

The odds we expect depend on our detection ability. Maybe there are thousands of these objects but we saw this one only because it passed so close to Earth.

There is fairly strong consensus in the astronomy community that possibly hundreds of Sednoid class objects exist, and those are in relatively normal orbits compared to things which are beyond solar escape velocity. But so far we've only found 3 or 4 Sednoids.

https://en.m.wikipedia.org/wiki/Sednoid

Sednoids orbiting in the kuiper belt are totally different from extrasolar objects on hyperbolic trajectories. Oamuamua passed inside Mercury's orbit.

Yes, but both classes of objects are very dificult to detect, due to distance, size and lack of brightness. We only detected the extrasolar object once it had already passed perihelion and was on its way out.

"Such an intrinsically faint body could be discovered only thanks to the close Earth flyby in October 2017, which created a tremendous opportunity for the first detailed characterization of a minor object of exosolar origin."

https://arxiv.org/ftp/arxiv/papers/1712/1712.00437.pdf

If you're right about the spin for alignment, we should be looking into deep space in the direction of it's axis. Presumably, this direction is erratic but there may be orientations that dominate over time.

A tumbling probe that doubles as a cosmic pointer to home. Cool.

There's another little fun point here. If this was a probe, the point where you'd accelerate to have the greatest effect on your trajectory would be exactly where it did - at one of its semi-major points - where its trajectory turns.

What’s special about 0.163 AU? Does it have a mathematical significance?

AU stands for Astronomical unit, and it's used for measuring distances in space smaller than light-years. 1 AU is the distance between the Earth and the Sun. 0.163 AU tells you how close it came to earth.

I'd prefer to use light seconds/minutes for that. Not only it's easier to grasp (0.163 AU seems awfully close, but 81 light seconds sounds reassuringly far) but it'll probably be more helpful when we have to communicate across these distances.

Just that it's unusually close.

As we are in paranoid mode (and it's fun to be, isn't it?): not only it's unusually close, but it seems that Earth is the planet it pass closer in all the Solar System.

Maybe somebody should check if that "slightly acceleration" bring it closer or farther to Earth.

Maybe we have been photographed. I hope it's not that somebody shoot us and failed.

Aliens got us just before GDPR, sneaky bastards!

There is a bit of sampling bias, given that we are looking for space objects from Earth, and so it easier to detect something that comes closer to Earth. Not sure how significant the bias is for an object of this size and speed, but I'm guessing that it is probably a relevant factor.

How could spinning rapidly possibly help for communication? Unless this distant companion is moving at many times the speed of light in a massive ellipse. Also, as someone else mentioned, rotational motion isn't intertial, it's not just relatively different from us on Earth.

Two more of them, and I'd say you have an excellent case.

They do everything in threes.

A Arc, B Arc...

I want this to be an alien ship so badly!

> what are the odds?

100%, because it happened

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