Earth Orbit

From another post, I was called out on my assertion that the planet Earth could be knocked off its orbit of the Sun.

Isn’t it possible (one might say, even likely) that at some point another celestial body will collide with Earth with enough force to send her spiraling out into deep space?

Galaxies collide, wouldn’t you have to assume that planet sized bodies occassionally meet like two trains on the same track.

I would imagine that any object large enough and travelling fast enough to send the Earth spiraling out of the solar system would be far more likely to obliterate it so it resembled galactic gravel. I would imagine that a significantly large object could alter the orbit of the Earth either closer to or further away from the Sun or change it’s shape but as for changing the orbit so much that the Earth escaped the solar system and effectively stopped orbiting the Sun, nope, don’t think so.

You don’t need a impact to throw a planet out of orbit. A passing star would work just as well.

The problem is, of course, that we’re really small, space is really big and there’s ample rooom to “miss”. Even in colliding galaxies, there’s rarely a stellar collision.

Possible? Of course.

Likely? I wouldn’t think so, what with the huge distances of interstellar and intergalactic space. So while it is possible a huge mass could come close enough to throw the earth out of its orbit (actually hitting the earth is not required), the odds against it are, well, astronomical.

That would’ve been me, and I misunderstood what you were saying. Actually it did seem like you were suggesting the Earth just wander off nonchalantly, you didn’t make it clear you were talking about a collision.

Collisions OTOH are perfectly possible - I think the latest ideas on the moon, are that it formed from a collision of a massive body with the proto-earth. Such an event could certainly drastically alter the earth’s orbit, not sure it could kick it out of the solar system altogether though.

And in the context of your original thread, you were enumerating ways that we might all be fucked in the future. But if a collision on that scale occurred, the shift in the Earth’s orbit would not be our immediate worry!

HTH.

A small nudge would send a planet into a more elliptical orbit. A big nudge would send it into an even more elliptical orbit. It takes a huge push to get it completely out of the solar system. The earth’s orbital speed is about 30 km/s now, and you need to get it up to about 42 km/s for it to break free. (Just for reference, speed of sound is about 0.3 km/s, and the Space Shuttle’s orbital speed is about 7 km/s.)

In the early history of the solar system, they did. That’s the current theory of how the Moon formed.

But now, all the planet-sized bodies in the solar system are in stable near-circular orbits around the sun.

I don’t know for sure, but I suspect a collision with something comparable in size to the Earth is more likely to pulverize the Earth than knock it out of its orbit. It would certainly kill off all life on Earth a long time before we had to worry about changes in the orbit. The asteroid or comet impact that killed the dinosaurs wiped out something like 95% of all living creatures on Earth at the time in one way or another (note: this refers to individuals, not species), and it was only 10 kilometers or so in diameter. Earth is about 6400 kilometers in diameter, Mars (which is about the size of the object that hit the Earth and caused the formation of the Moon) is about 3400 kilometers in diameter.

A close encounter (not even necessarily a collision) with a star could knock planets out of their orbits (here’s a cool simulation of what might happen). But close encounters between stars that don’t start off as binary stars or something like that are incredibly rare. Even when galaxies collide, there’s just so much space between stars (except at the centers of galaxies) that encounters that close between stars just don’t happen. They could happen, but they’re very unlikely.

(here’s a cool simulation of what might happen). But close encounters between stars that don’t start off as binary stars or something like that are incredibly rare. Even when galaxies collide, there’s just so much space between stars (except at the centers of galaxies) that encounters that close between stars just don’t happen. They could happen, but they’re very unlikely.
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That simulation is pretty cool, thanks.
And if it happened, I imagine things would get very very cool, and dark.

There’s a classic sci-fi short story by someone I can’t remember about this scenario, called “A Bucket of Air,” IIRC. A passing star has dragged the Earth away into deep space, and the few survivors are living in an air pocket in a building that they keep going by digging into the frozen atmosphere, one bucket at a time. They have a fire going in their pocket and they place the bucket of frozen oxygen nearby to thaw out and keep them going. Kind of interesting.

Collisions are a kind of catch-all in planetary science, IIRC:

Venus rotates retrograde? Collision!!

Earth got a big-ole moon, similar in composition to the earths mantle? Collision!!

Uranus all knocked over on it’s side? Collision!!

The point being, large-scale collisions are considered likely enough to make it into many theories, especially in the ‘childhood’ of a solar system.

By Fritz Leiber. And yes, a very good story.

And Pluto and it’s large (relative to the planet) moon. Collision!! (The two recently discovered moons don’t seem to have altered this theory.)

But there is at least one other theory about Venus’s retrograde rotation: solar tides acting on its dense atmosphere. Not sure what the curent status of this theory is.

About the Mars-sized object that collided with the Earth to form the moon, note that Mars has about one tenth the mass of the Earth. AIUI, this collision was enough to melt surface of the Earth to a depth of around a kilometer.

The story title is “A Pail of Air”, not “A Bucket of Air” for those who want to look it up.

When I was watching the simulation (cool link, btw) I couldn’t help but notice it’s 2 dimensionality. Would a large body coming in off plane to the solar system be more detrimental?

Actually Hombre, it is 3D. Try messing with the scroll bar on the right. After I discovered that I ran the sim several more times just to see it from different angles. Way cool!!

I was wondering . . . what is the time frame for this occurrence? How long would it take from the moment the large object gets close enough to the earth till the time we notice that spring break is over? Minutes, hours, days? Or would we all be dead before we noticed anything was wrong?