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What I want to know is if an asteroid about 15 KM in diameter and roughly double that in length, spinning at a significant speed, could go undiscovered until a crew of an asteroid mining ship happened upon it, out in the belt (specifically the Mars/Jupiter belt, not the Kuiper belt).

A little bit of extra information that may or may not affect this likelihood - man at the time of this story does have a significant population in space, with Earth-orbital colonies, a few lunar and Martian colonies, and a significant presence out there in the belt. The belt is so huge and vast and so full of objects though, could an asteroid like this, that's not exceptionally bright/reflective, go unnoticed until stumbled upon?

[EDIT] The spin would be maintained artificially. Technology is present the humans won't fully comprehend, and thus I don't have to fully reconcile. Presumably, this would also prevent it from going into a tumble.

[EDIT #2 - Shame on me for needing to revise this twice!] BeauM raised a point I should've thought of, and that's specifying the level of advancement/time period for humanity in this case. I place this around 175 or so years into the future, which I see as an awful optimistically short period of time to be where they are with space colonization really. But it's possible. They've got nuclear propulsion working well enough to reach Mars in a couple months when it's at its closest. They've got decent laser drills to carve asteroids up, and they've got decent centrifugal "gravity" on ships and orbital stations to make space habitation comfortable. But they've not achieved any magical leaps in technology. Telescopes aren't all that much more powerful than our newest exoplanet hunting setups, they merely have the opportunity to put more of them in more advantageous places. Really the only fantastic leap, which made space so much more accessible, was the construction of decent magnetic launchers to escape Earth affordably and mostly safely.

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    $\begingroup$ I am no expert, but small size and "not exceptionally bright/reflective" make lack of discovery quite possible. I do not think spin has anything to do with it; in fact if it spins too much, "centrifugal" force will rip it apart. $\endgroup$ – Bald Bear Nov 11 '18 at 4:19
  • $\begingroup$ Right. I'm going for a spin that would produce about the "gravity" of Mars. Technically centrifugal gravity isn't actually gravity, but functionally, it may as well be. I suspect that much spin isn't enough to rip it apart, especially at that size? $\endgroup$ – Cereza Nov 11 '18 at 4:26
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    $\begingroup$ .Please put that info in the question By the way, a spinning asteroid doesn't produce more gravity, unless you mean inside an hollow spinning body $\endgroup$ – L.Dutch - Reinstate Monica Nov 11 '18 at 6:21
  • $\begingroup$ this question might help / is similar: worldbuilding.stackexchange.com/questions/37746/… $\endgroup$ – if-trubite Nov 11 '18 at 13:03
  • $\begingroup$ The answer is "no", but maybe you could have it that the protagonists ingeniously manipulate the data in the various scientific / mapping database so that it remains "unknown" ........................ :O Spooky. $\endgroup$ – Fattie Nov 11 '18 at 14:26
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Most likely, no

There are approximately 10,000 asteroids over 10 km in radius in the main asteroid belt (Masiero et al., 2011; Figure 5).

There are 636,499 identified objects in the asteroid belt as of May 2015 (Jones et al., 2015).

We have almost certainly detected every asteroid in the main belt (and the inner solar system, too) that is larger than 10 km in diameter.

If you want this to be true, for fiction reasons, I'm sure you can make something up, but that would be the topic of a separate question.

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    $\begingroup$ Fair enough. Let me ask this - which I don't want to start a whole other question for right after making this one - is it possible a severe axial spin could go undetected? Most objects, this is measured by the fluctuations of its brightness. If it's not very bright to where this is fluctuation is severe? $\endgroup$ – Cereza Nov 11 '18 at 4:32
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    $\begingroup$ @Cereza If the asteroid is spherical, and has a similar albedo on all sides, then there is little variation in the is brightness, so it would be hard to tell what its rotational speed is. $\endgroup$ – kingledion Nov 11 '18 at 4:44
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    $\begingroup$ @kingledion, although to be fair, astronomers are pretty good right now at measuring rotation of an object in the solar system if they can see it. $\endgroup$ – Keith Morrison Nov 11 '18 at 4:53
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I agree with the No answers regarding detection, but like some other recent answers by me I wonder if recognition may be missing. That is,

  • the asteroid has a catalog number in astronomical databases,
  • there is a rough size estimate,
  • rotation speed may or may not be known with any precision,
  • but no human analyst ever looked at the data in any detail.

Data mining is an extremely powerful tool, but as of today it mostly finds what people train it to find, intentionally or unintentionally.

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    $\begingroup$ In general, I would agree with this, but since the question mentions a mining crew arriving at the object, it is probably safe to assume that someone had a look at the data beforehand, even if it's just the crew. $\endgroup$ – mlk Nov 11 '18 at 15:26
  • $\begingroup$ @mlk, the mining crew "happened upon it." Doesn't sound very pre-planned, but then space is too vast for many chance encounters. $\endgroup$ – o.m. Nov 11 '18 at 15:31
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    $\begingroup$ Yeah, that's true. I interpreted "happening upon it" more in the sense of the asteroid being an intended target, that just turned out to be not as ordinary as thought. $\endgroup$ – mlk Nov 11 '18 at 15:33
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    $\begingroup$ I had the same question (whether anyone would notice it if it was catalogued and filed away in some database). See my answer for the reason why I think it would be flagged, even by automated methods. tl;dr: spin rate would be so far outside of the normal distribution for objects of its size. $\endgroup$ – ben Nov 11 '18 at 18:57
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Yes, if you hide it inside another asteroid

This may sound like cheating, however I have some reason behind this madness. There are many problems with hollowed out asteroids as space stations. If you are thinking long term, you want a thick shell, to avoid damage by the occasional impacts of smaller asteroids. You also want the inside to be even, even if the outside isn't. All this makes the shell needlessly heavy, requiring a lot of energy and reaction mass to get it to rotate. There is also the structural problem, since you do not know how the shell will react to the stresses of centrifugal forces. Also whenever some maintenance guy working on the outside drops his wrench, it will be catapulted off to who knows where...

You could of course use up the whole asteroid to simply build a well armored rotating space station, however this would kind of defeat the purpose. Instead an advanced space-faring civilization might combine both approaches:

  1. Hollow out an asteroid. Leave a thick enough shell to withstand whatever impact you think might occur and only leave a small opening at one end. (maybe put an angle in there to avoid freak asteroid-strikes.)
  2. Build a lightweight cylindrical space station inside the asteroid and affix it at the ends with some alien, frictionless, superconducting magnetic bearings.
  3. Spin up just the inner space station, leaving the shell motionless.

This leaves you with artificial gravity inside, a solid shell and even some protected zero-gravity parking spaces for you spaceships inside the cavern (Think of the insurance bill). It also solves the wrench dropping problem.

(I remember having already read about an idea like this somewhere else, however I do not remember a source)

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    $\begingroup$ That might solve the rotational issue, but I fear that now the rock might radiate enough IR to be interesting to astronomers. $\endgroup$ – dotancohen Nov 11 '18 at 18:36
  • $\begingroup$ This is an interesting idea, and one I hadn't thought of. $\endgroup$ – Cereza Nov 11 '18 at 20:46
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    $\begingroup$ @dotancohen If it radiates enough to be interesting in this configuration, why would it radiate any less with the more brute-force, spin-the-whole-thing method? $\endgroup$ – Logan R. Kearsley Nov 11 '18 at 22:29
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Almost certainly no. Aside from Kingledion's answer regarding discovery with existing and older technology, by the time there's a significant human population in space puttering around, it wouldn't be unreasonable to assume that anything signficant in size (say over 100 meters) within the orbit of Jupiter would be cataloged.

Second issue, the spinning. Due to rotational effects, a cylinder (which your asteroid is, roughly speaking) is unstable rotating along its long axis and will eventually start tumbling around its short axis (see this question here explaining why). That means the asteroid will be tumbling end-over-end, which means changes in the area exposed to light and any observer, thus the rotation will be trivially visible even if the surface has a uniform albedo and is otherwise featureless.

Unfortunately, your asteroid will be known about long before anyone ever gets there.

EDIT

Taking into account some of the clarifications, here's some other problems:

  1. If it's just been found by a mining crew, that immediately raises a concern about why it wasn't already catalogued, because it clearly should have been.

  2. If it's being stabilized by the inhabitants to prevent tumbling so it only rotates around the long axis, that's going to raise flags all by itself because of not rotating around its short axis as a natural object would. That would instantly be a screaming indication something is wrong.

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    $\begingroup$ If I guess the narrative intent correctly, let's suppose someone is making use of this asteroid as a home. In that case, considering the advanced engineering required to inhabit an asteroid, the spin along the long axis may be stabilized (see solutions in the link you provided - notably altering density to change primary spin axis). So assuming stable spin along the long axis would the spin still be likely to be detected? $\endgroup$ – ben Nov 11 '18 at 5:53
  • $\begingroup$ @ben Well, there's something in there yes, and the source of this something is significantly more advanced than the people that find it. There's nothing alive in there, but it's intended to accommodate living things, though not as a permanent habitation. $\endgroup$ – Cereza Nov 11 '18 at 6:01
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    $\begingroup$ @Cereza If it's an artificial/engineered asteroid produced by those with technology significantly ahead of what humans would have in 175 years, then that significantly changes the question. I mean, with technology that advanced, you can basically assume magic; if the makers don't want it to be found, it won't be found. $\endgroup$ – Nat Nov 12 '18 at 4:19
  • $\begingroup$ Even advanced tech has to obey the laws of thermodynamics. If the thing in inhabited, meaning life-support, meaning power....where does the waste heat go? The thing will be glowing in the infrared compared to anything around it. See any discussion about stealth in space. $\endgroup$ – Keith Morrison Nov 12 '18 at 20:58
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Implications of Detection

Detection has been fairly well-covered in other answers, so I feel like I should address the "what-if" in the case that your asteroid is catalogued and characterized.

Roughly speaking your asteroid would need to be spinning at ~0.02224 rad/s (0.00354 rev/s, 0.21252 rev/m, 12.751 rev/h, 306.03 rev/d, etc...) to generate the equivalent of Mars surface gravity against the inner walls - if it has relatively thin walls.

I am not a materials scientist, but it does seem that the size you propose is small enough to not become a sphere under its own gravity. Whether a rocky body could naturally stay cohesive under this spin rate is out of my wheelhouse but my guess is it would.

This paper does a nice job of comparing size to rotation rate (just look at the plots to get all the info you need). Unfortunately, it seems that for an object over 100m there is a max observed spin rate of ~10 rev/d. If astronomers found a cylindrical asteroid 15km by 30km spinning at 306 rev/d you can bet they'd be taking a REAL close look.

**EDIT: I originally used 15km as the radius, now the calculated values reflect a diameter of 15km.

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While I generally agree with everyone else's conclusion of no, I'd like to add a maybe, a rather tenuous yes.

Sure, we have detected to date 636,499 objects tumbling about in space, but how long has that taken us? The first asteroid was detected in 1801, and we didn't really start detecting asteroids "en-masse" until somewhere around the mid 1990's to early 2000's. That leaves 200 years of wiggle room for something to hide, which brings me to my next point that space is big. You have to be looking in the right place at the right time to really find something. Given your beings have already colonised the nearby surrounding heavens, the level of technology would be more advanced than we have today and as such detection methods would likely be greater. However what this may not mean is that vast amounts of time and man-power have gone into looking at the area that you're interested in.

Maybe it's not located around or near another populated area and doesn't get much interest from researchers. Maybe it's on the other side of something larger, that just refuses to get out of the way in any timely fashion. Maybe it's near a militarized zone, and looking in that direction too closely with a powerful telescope will bring about the unwanted attention of men in black coats driving black cars. Maybe it's just a new area for researchers, and the task of identifying all these tumbling dark objects is large and daunting, therefore slow work.

This all depends on the level of technology you have portrayed your beings to have. If they scanning the skies and detecting in-coming enemies from another far off planet for example, the above is probably moot.

[EDIT]

Based on your recent edit, I feel there's a higher chance that something would simply not be seen, in any decent time-frame anyway. The time between detecting, identifying, cataloging, explaining, and then releasing of information can be hilariously long. Especially if there is something anomalous about the object, something that can't be explained with science of the day, something that might be noticed but remain solely with one or two scientists who are trying to solve the mystery before releasing the information to the world.

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    $\begingroup$ You raise an interesting point, and I maybe should have been more clear about the technological development of humanity at the time. That said, I'm going to make another edit to the question to clarify that. Also, welcome to the worldbuilding stack exchange! $\endgroup$ – Cereza Nov 11 '18 at 23:30
  • $\begingroup$ edited my reply accordingly, and thankyou. $\endgroup$ – BeauM Nov 12 '18 at 0:05

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