Lois & Clark Forums Forums Fan Fiction Fanfic Challenge 101 uses for a large asteroid...

This is really one for the SF fans.

It occurs to me that Nightfall is a wasted opportunity, especially if Clark can find a way to divert it rather than destroying it.

The big problem was the shortness of the time between its discovery and impact; let's assume, for the sake of argument, that it's discovered just after Superman goes public, with several weeks or months before impact. That gives a much longer time for small course changes to take effect; if Clark can fly that far with breathing gear, a few hours of gentle (for Clark) shoving should be enough to steer it clear of the Earth. But inevitably someone is going to have bigger and better ideas.

You see, there's this neat idea called an orbital tower, and the essential starting point is a really big asteroid in a 24-hour orbit over the equator...

It's an enormous project, and getting it exactly into place will need Clark to make repeated flights into space throughout the approach of Nightfall. At first there's huge excitement, but gradually people start to grumble because he's spending less time stopping crimes in Metropolis. Naturally Clark has huge problems juggling his job, the asteroid project, and Lois.

Meanwhile Lex is doing everything he can to get the contract to build the orbital tower (and yes, the technology is extremely dangerous if it goes wrong), the UN wants it to be globally owned while the USA wants it as an American project, Bureau 39 think that Clark is bringing in the Mothership, etc. etc.

I think it could be an interesting story, we've never really seen Clarke involved in a project that will take years to reach fruition, but right now I'm so far behind with other stuff that I can't possibly write it. So I'm throwing the idea out as a challenge.

Your essential reading here is Arthur C. Clarke's "The Fountains of Paradise"; Charles Sheffield's "The Web Between The Worlds" covers some of the same ground but isn't as useful.

Interesting idea, though not without its problems. Being so irregular in shape, Nightfall might not be a very stable anchor mass (remember those gravitational anomalies that made ACC move Sri Lanka to the equator as the fictional Taprobane?). I'd also be concerned about where the tower materials were going to come from, but I guess we could presume that suitably strong stuff has been invented.

Alternatively, how about using Nightfall as the basis for an O'Neill-style space station/colony? Prometheus would be a tiny little tin can by comparison. If we used the original idea, Superman could place the water bags inside the asteroid, and his heat vision could even help the melting process -- in fact, he'd be useful in smoothing out irregularities so that the finished "cylinder" was even in thickness, before and after the water bags blew. And then he'd be needed (or wanted) to cut hatches, help move in the ecology, etc., etc. I suspect that putting it in the L4 or L5 positions might be a bit too advanced for EPRAD, but it'd make one heck of an orbital habitat.

Failing that, simply mine the thing! Place explosives and carve it into managable chunks which could be parked in a convenient orbit. What's the current price of nickel? Bet it would drop with a 17-mile long asteroid made of nickel-iron available! And who knows? It might have other, more valuable minerals inside.

Nightfall was not a threat to the Earth. Anything that gets between the Earth and the Sun, which Nightfall did since it blocked sunlight, is already past us and can't turn around and come back.

In relation to the Earth the Sun is downward.

Think of the Sun as the ground, and Earth as a high flying plane. Nightfall would be between the plane and the ground. Not a problem.

Therefore somebody was lying to Clark!

It was clearly an attempt to trick Superman into killing himself trying to save Earth.


Patrick

Patrick, this theory looks very interesting!!

I'd love to see that in a fic.

See ya,
AnnaBtG.

Not original with me. A number of people have worked it into stories.

Got any examples?

Thanks,
AnnaBtG.

It could spiral in if its trajectory was at the correct angle, but I admit that that's a bit iffy and would require some serious computation to check if it would work.

Not so. The Earth has its own gravity and there's a point at which it becomes stronger than the Sun's -- or we'd all be falling into the Sun! A better analogy would be to adapt the relativistic rubber sheet model: think of the Sun and Earth as two valleys; the Sun valley is deeper than the Earth one, but something that moves past the "lip" between the valleys is going to fall into the Earth, not the Sun.

Yes, the physics of the episode is dodgy -- but then, what can you expect from a space agency that comes up with such a stupid way of dealing with the problem? A little lateral shove at a far enough distance and Nightfall becomes just another NEO -- a slightly big one, but no more trouble than any other.

Phil

> The Earth has its own gravity
> and there's a point at which it
> becomes stronger than the Sun's
> or we'd all be falling into the Sun!

Nope, we all ARE FALLING into the sun, we just keep missing it. That's what an orbit is. If we could stop the Earth and hold it still everyone sun side would fly off the Earth into the sun. The Sun's gravity is stronger.

Anyways for nightfall to block out the sun it would have to be too far past the Earth to ever come back.

However you could have two rocks, the first which is spotted and we know will miss but as it gets closer we discover it was blocking our view of a second that will indeed hit the Earth.

The first is the one that blocks out the sunlight and the second the one Superman has to stop.

But hitting it is still a poor idea. We could have him hit it with his ship, flying it up and using it like a wedge.

Or we could have him push it faster so that it misses the Earth arriving to the intersection point of Earth's orbit much earlier than the Earth and thus mssing the Earth.

And that would be easier than smashing it or pushing it off course.

True enough. I would bet good money that Phil knows this, however, and was simplifying. (Please note his listed location.)
Definitely false. Newton\'s Law of Universal Gravitation states that not only do the masses matter (and certainly the sun has WAY more mass than the earth), so does the distance (or rather, its inverse) -- squared!

The pull of the earth on you (or me, or anyone on our planet) is far greater than that of the sun.

Now, if the earth somehow shed all its (tangential) velocity, we would indeed go plunging into the sun. Because the EARTH would, and we along with it!


There's a rule that extra-solar objects must enter our solar system from one specific direction?

Not that I am aware of but to be in position to block sunlight it must be between the earth and the Sun.


The measured gravitational acceleration at the Earth's surface is found to be about 980 cm/second/second.
<http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html>

The sun's gravitational pull on the earth is proportional to 2 x 10^30
/ (1.5 x 10^8)^2 = about 8.8 x 10^13kg

But without more work I'm not certain how to compare the two sets of numbers.

Well, the mass of the Sun is about 300,000 times greater than the mass of the Earth. The radius of the Sun is about 100 times greater than the radius of the Earth. This means, I believe, that the gravity at the surface of the Sun might be about 30 times greater than the gravity at the surface of the Earth.

Gravity always pulls us towards the center of a particular gravity well. Any massive object creates its own gravity well around itself, and the "bottom" of the gravity well is at the center of the massive object itself. The closer you come to the center of a massive object, the more strongly its gravity will act upon you.

Here is the implications of that. Consider the Moon. The mass of the Moon is only about 1/80 of the mass of the Earth. You might think that that should mean that you would only weigh 1/80 as much on the Moon as you do on the Earth. Suppose a person weighs 80 kilograms, a fairly average weight for a grown man who isn't too overweight. If the mass of the Moon is only 1/80 of the mass of the Earth, you'd expect the man who weighs 80 kilograms on the Earth to weigh just 1 kilogram on the Moon!

However, that is not the case. A man who weighs 80 kilograms on the Earth will weigh about 13 kilograms on the moon. The reason for this is that the Moon is considerably smaller than the Earth, and therefore the distance from the Moon's surface to its center is smaller than the distance from the Earth's surface to its center. Simply because an astronaut on the Moon is closer to the Moon's center of gravity than we Earthlings ever get to the Earth's center of gravity, the astronaut simply feels a lot more of the Moon's gravity than we Earthlings feel of the gravity of the Earth

How much would we weigh if we could burrow all the way into the Earth's center? I believe the radius of the Earth is about 6,000 kilometers, which means that the center of the Earth is about 6000 kilometers away, straight down into the Earth. Gravity increases with the square of the distance, or so I believe, and 6,000 squared is actually 36 million!!! Does that mean we would weigh 36 million times more at the center of the Earth than we weigh at its surface? People, I have no idea if this is the correct way of counting and calculating.

But I am sure of two things. One, we would indeed weigh a heck of a lot more at the center of the Earth than we do here at its surface. And two, don't worry about the gravity of the Sun. It will not lift us off the Earth and send us plunging into the Sun. Sure, the Sun contains 300,000 times more mass than the Earth, but the mass center of the Sun is 150 million kilometers away, a very safe distance indeed! So, no worries, people, the Sun is not a body snatcher!

Ann

Actually, at the center of the Earth you weigh precisely NOTHING!

Here\'s why.

You know I think I remember a cartoon that actually got that kind of right. I may just be remembering wrong but a character was falling towards the center of the Earth and once he went past it he yo-yo'ed back up. But instead of going back to starting points the characters back and forth lessened till he was floating at the center.

Yes, Rivka, you are right that if you were sitting at the very center of the Earth, the Earth's gravity wouldn't try to move you away from your location, and so it wouldn't pull at you. If we define "weight" as the strength of the force with which gravity is pulling at you to change your location, then it is clear that you wouldn't weigh anything at all at the center of the Earth.

By the same criterion, you would weigh absolutely nothing at the center of a black hole. You would, however, be squished to a mathematical point. Even sitting at the center of the Earth, you would, for all your weightlessness, feel very heavy, compressed and trapped, with the entire mass of the Earth pressing in on you from all directions!

So, Rivka, you would weigh nothing at the exact center at the Earth. Is it at least theoretically possible, then, that if you were sitting an inch away from the center of the Earth, you would indeed weigh 36 million times as much as you do on the surface of the Earth, say, at sea level?

Ann

Sorry, no, it's nothing like that simple. Gravity rises for a while as you go down then decreases again - I can't without checking remember where it starts to decrease, but I have a feeling that I remember it as being about two thirds of the way towards the centre of the earth. If you could get to the centre of the earth without being crushed - presumably through a tube with some sort of force field as walls - you'd be in zero gravity by the time you reached the centre, but pretty close to zero gravity for miles either side.

Marcus, you are right that gravity would steadily decrease as you burrowed deeper and deeper into the Earth. A math teacher just explained it to me. The thing is, the mass that is above you would pull you in the opposite direction of the mass that is beneath you, and the deeper you burrowed, the more mass would be above you.

If we could compress the Earth, so that it still contained the same mass but had a smaller radius, then gravity would pull at you more strongly when you were standing on its surface than it does today. Or so I really believe anyway. I think that, in math-speak, you would say that a smaller Earth with the same mass would have a steeper gravity well.

Gravity as a function of mass and distance is a really tricky business. Imagine, for example, that we could shrink the Sun into a black hole. If this happened, the Sun would get an incredibly steep gravity well, pulling everything inside that ventured too close, and crushing every hapless incoming morsel into nothingness. But the Earth would not be pulled inside. Why not? Well, because we are not pulled inside today, and the Sun's total gravity would not increase if it became a singularity. We are in a stable orbit around the Sun, and that wouldn't change if the Sun turned into a black hole.

Imagine what would happen if the innermost core of the Earth became a black hole. I believe that the black hole core of the Earth would start eating up the rest of the Earth, but because this black hole would be extremely tiny, it would only be able to swallow tiny morsels at a time. In other words, the inner black hole would inexorably eat away at the Earth, but it would take a long time before it affected the surface of the Earth, where we live.

On the other hand, a black hole Earth would never be able to swallow the Moon, because the Moon is too far away from the Earth, in a stable orbit around it. Or so I believe at least, but as you've seen, I've been wrong before! So if I got this wrong too, I'd appreciate it if anyone cared to enlighten me!

Ann

If the Earth became a black hole (which it couldn't very easily; there isn't enough mass in the earth to make one that would be stable) there would be no affect on the orbit of the moon at all. The only difference would be that the rotational centre of the Earth and the Moon - the point where the gravity of the Earth and the Moon pull equally, around which they rotate - would be a few thousand miles above the black hole in the direction of the moon, rather than a few thousand miles underground as it is at present.

Thanks, Marcus. Yes, that makes sense.

Ann