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For Science Geeks Only

Joined
Oct 20, 2016
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7,045
#1
The Physics Behind the Strange Interstellar Asteroid 'Oumuamua

This is probably not what 'Oumuamua looks like.
ESO/M. Kornmesser
For the first time, humans have detected an interstellar asteroid—a space rock they're calling 'Oumuamua, which is a Hawaiian word meaning "scout." It's the only object we've ever seen that entered the solar system from beyond our little collection of planets. That's a pretty big deal on its own. But on top of that, this asteroid has a really interesting shape: It's very long and skinny, with a width to length ratio of about 1 to 10.

Basically, it looks like a cigar—or at least that's what everyone is saying. The only images we have that show its shape in detail are artistic renderings. Because the asteroid is so relatively small and far away, you can't easily see it with a visible-light telescope.

But if you can't see it, how can you describe it? The answer to this (as in many situations in science) is to use indirect observations. The one thing that can be measured is the brightness of the object. Because this rock is also spinning, the light it reflects from the sun changes over time. By looking at the ratio of the brightest to weakest observations, you can get an estimate of largest to smallest size. If you estimate the albedo (a measure of reflectance), you can also estimate the total size. Boom. There you have it—a cigar-shaped asteroid.

If you want to learn the answers to more "how do you know"-type questions about 'Oumuamua, check out this awesome NASA FAQ. But if you want to calculate some answers for yourself—well, just keep reading.

Could this be a spacecraft?
OK, everyone calm down. This isn't a page from Rendezvous with Rama—an Arthur C. Clarke novel that depicts an interstellar object that happens to be an alien starship. But what if it was a spaceship? Could its rotation make a type of artificial gravity?
https://www.wired.com/story/the-physics-behind-the-strange-interstellar-asteroid-oumuamua/

He poses some questions toward the end of the article.....Anyone want to take a shot at them?
 
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#2
Sounds interesting if your into conspiracy theories.
Spaceships from outer space.
You got a good one going here.
 

Knotical

Shepherd of the Knotical kid-farm
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#5
I for one welcome our new cigar-shaped, artificial gravity creating, overlords.
 
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#6
I for one welcome our new cigar-shaped, artificial gravity creating, overlords.
Me too! I aint skeered of them scrawney little aliens. They're demonic and so thus easily controlled by a spirit filled Christian in the name of our Lord...

That's why you never hear about Christians being "abducted"...they'd get shut down fast as soon as Jesus name was dropped!
 
Joined
Oct 20, 2016
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7,045
#9
Anyone willing to take on his 'homework'?
Homework
  1. How fast would this asteroid need to rotate such that people inside would experience an apparent weight half that of on Earth? Note: Here are some rotating space craft from science fiction—just for fun.
  2. If a human was standing inside this asteroid (that's actually a spacecraft), could that human jump from one side of the ship to the other?
  3. Assume 'Oumuamua has a uniform density like a rock (you pick your favorite rock). How much energy would it take to get it rotating at the current angular velocity?
  4. If you are standing at one end of the rotating spaceship, how fast would you have to throw a baseball such that it makes it to the other side without hitting the wall? Hint: Think about the Coriolis force. You might need to make a numerical model, but you could probably do this with a rough estimation.
  5. Create a Python model showing the rotating 'Oumuamua as it moves through the solar system. You can model the solar system as just the sun and Jupiter.
  6. Suppose we want to rendezvous with 'Oumuamua—which would be a cool title for a book. How fast would the spacecraft from Earth have to travel in order to catch up with 'Oumuamua before it leaves the solar system? How long would this trip take? This one is difficult.
  7. Super large asteroids are spherical, but this one is not. Calculate the net gravitational force on a part of the asteroid to show that it is much smaller than the bonding forces of a typical rock.
  8. As 'Oumuamua moves past the sun, it has two types of angular momentum. There is the orbital angular momentum and the spin angular momentum. I believe (but I'm not 100 percent sure) that the total angular momentum of spin plus orbit should be constant. Estimate the change in spin angular momentum as it passes the sun (due to tidal gravitational forces). Should this change the orbital angular momentum?
  9. Why is this asteroid so skinny? Make up a plausible story to explain its shape.
 
Joined
Apr 13, 2014
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Christian
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#11
1) One rotation every 7.7 seconds using a radius of 15 meters for normal earth gravity. Coriolis forces at that rate generally affect inner ear functioning. It would not be practical for a human ship.

Slowing it down to 19.23 seconds per rotation would give half gravity.
 
Last edited:
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#12
2) This is a trick question. Rotation isn't actually gravity, so its not a simple matter of calculating how high you can jump at 1/2 G. You have to remain tethered to the outer surface to experience 1/2 G. If you were in the middle of the craft, you would be weightless. Once you leap into the air, the centripetal force you experience immediately changes, because the craft is no longer dragging you along its inner surface. In addition, the other side of the craft you were trying to reach continues to rotate to a new position. Even if you could leap fast enough to move 30 meters, your target would have moved to a new position by the time you got there. When you finally did reestablish contact with the outer surface, you would be going at a different velocity than the surface, and would tumble out of control until you could grab onto something.

So the practical answer is that this is not something you would ever want to try, for safety reasons. You would want to wear special shoes that keep you firmly tethered to the surface at all times, and slowly walk around the surface to your goal.
 
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#13
2) However, if you wanted to throw a baseball to a target on the other side, you would not throw the ball straight up. If you simply let go of the baseball, it would continue in a straight line until it reached the curved surface. To the astronaut it would appear to move to the surface, but not to the surface by his feet. Off to the side. Throwing the ball straight up would make it appear to take a curved path to the side of the target. You would have to throw the baseball at an angle, compensating for the momentum of the baseball due to you holding it while tethered to the surface. Also you would have to allow for the target continuing to move in the direction of rotation after the baseball leaves your hand. So you could throw a baseball to a target on the other side of the craft, but you would have to throw it at an angle, not straight up.

I suppose you could try jumping at that same angle to reach the target, assuming the target had a cushioned sticky surface to grip you when you got there...
 
Joined
Oct 20, 2016
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#14
2) However, if you wanted to throw a baseball to a target on the other side, you would not throw the ball straight up. If you simply let go of the baseball, it would continue in a straight line until it reached the curved surface. To the astronaut it would appear to move to the surface, but not to the surface by his feet. Off to the side. Throwing the ball straight up would make it appear to take a curved path to the side of the target. You would have to throw the baseball at an angle, compensating for the momentum of the baseball due to you holding it while tethered to the surface. Also you would have to allow for the target continuing to move in the direction of rotation after the baseball leaves your hand. So you could throw a baseball to a target on the other side of the craft, but you would have to throw it at an angle, not straight up.

I suppose you could try jumping at that same angle to reach the target, assuming the target had a cushioned sticky surface to grip you when you got there...
Now your just showing off......:biggrin2
 
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Apr 13, 2014
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Christian
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#15
Since the earth is rotating on its axis, we are being dragged along with the surface of the earth, similar to being tethered to the inside of a rotating space craft. If gravity were to switch off, we would not gently float above the surface. We would continue in a straight line at about 1000 MPH, moving rapidly away from the earth. Something similar happens when you leave the inner surface of a rotating space craft. You continue in a straight line until you bang into one of the walls, bounce off, tumbling as the wall imparts spinning momentum to you. There is a reason nobody has actually built one of these things.