Using comets to alter the Earth's orbit

I caught the last half of John McLaughlin’s One on One on PBS this morning. FWIW, I don’t watch this show very often. He was interviewing the authors of The View from the Center of the Universe. I haven’t read the book.

The authors state that within 500 million years, the sun will become much hotter, and that the Earth will be fried unless we can shift our orbit further away from the sun. Not a terribly pressing problem, but luckily for us, they’ve come across a solution.

They propose using comets to alter the Earth’s orbit.


Now, I’m not in much of a position to judge the credentials of the authors, but I don’t see how this would work. One of them is a physicist at UC–Santa Cruz according to Amazon, but Amazon’s editorial reviews don’t inspire much conficdence somehow.

The authors didn’t go into much further detail of how you would accomplish this.

They suggested thay you would need to alter the trajectory of the comet somehow, but they didn’t suggest any methods for doing this. I suppose you could alter the Earth’s orbit a smidgen this way, but I’m not seeing a major orbital shift.

So- is this idea theoretically possible? Is it in any way practical, even supposing several millenia of technical advances?

Planet Earth on the move

Paging Angua.

Each individual pass by a comet or asteroid would make a very small difference. But 500 million years is a long time to make passes in, and eventually, they’ll add up. For changing the orbit of the comet, you can use any of the standard methods for moving things in orbits: Rockets, solar sails, or the like. The trick is to make the change at the right spot in the orbit: A small rocket boost at apohelion can lead to big changes down at perihelion.

500 million years?? That sounds a bit short - I’ve always learned that our sun has been around for 5 billion years, and will turn into a Red Giant in another 5 billion years, at the end of her natural life circle.

Even in 500 million years, I guess that mankind has better mastered dealing with comets, asteroids etc. well before that (otherwise one “Armaggedon” will do us in), so moving Earth itself a bit farther shouldn’t be a problem then.

It’s not that the sun will die in 500 million years, just that it will get a lot hotter. IIRC, the orbital move will have to be repeated every 6,000 years.

As Chronos explains, even a small influence over a long timespan can result in significant changes, though I think you’d want to use something heavier and more permanent than a comet, like a larger asteriod. Better yet, you could cover the Moon with a network of high impulse rockets–maybe electrostatic drives run from solar power and using fine Moondust as propellent–and use it to drag the Earth into a larger orbit, which would offer better direct control over orbit modifications than occasional flybys from an interplanetary object. Or maybe you could build a giant mass-driver right through the center of the Moon and fling debris through it to get the impulse. (You’re going to want to give this stuff enough momentum, though, to achieve escape velocity from the Earth-Luna system or you’re going to have a bunch of crap floating around and mucking everything up.)

However, do these guys seriously think that in 500Myr we’re going to be worried about the fate of the Earth? Homo sapiens as a species has been around for about 250,000 years, and the whole Homo genus for roughly 2.5My–about 0.5% of the aformentioned period. In half a billion years, we’re either going to have expanded well off the planet and (likely) out of the Solar System, and/or we’re going to have evolved into something else (or wiped out completely, whether by our own actions or those of a successor). Saving the Earth from solar expansion, save for the sake of posterity, is a non-issue.

Besides, in 500Myr, we’ll have the technology to slingshot around the Sun at Warp 10 and go back to pre-historic Earth or something. Sure, you might have to wipe out a few cavemen and disrupt the 10 million year program that is running to solve the Question to Life, the Universe, and Everything, but we’ll know how to play a smashing game of cricket.


500,000,000 years? I’ll set aside the fifth Tuesday of every month for the rest of my life to worry about the prospect.
OTOH "What? Me worry? Alfred E. Newman

This reminds me of a fanciful speech by Harold Urey that I went to many years ago. As he talked I thought, “How nice it is to have won a Nobel Prize and have a sinecure so you can play games and travel around the country talking about them.”

This is the first time I’ve ever heard of something like this happening. Did the article provide a cite for this?

Besides, why wait 500m years? Everyone’s concerned about Global Warming, so let’s take this opportunity to knock the Earth’s orbit backwards a few thousand miles, problem solved. :cool:

This is typical behavior for main sequence stars like the sun:

It’s be easier to direct the comets, which are mostly ice anyway, into the sun to cool it down.

Danny Quayle, is that you?


I always appreciate the Douglas Adams Reference. Quite right, assuming we are here that long, we will have mastered not only the planetary slingshot effect, time travel, and cricket. We will also have mastered some very effective sun-screen which will render the harmful effects of such an increase in temperature triffling.

Envision the dog pulling down the swimsuit on the coppertone commercial? anyone?

Well, there aren’t enough Christians to do the job, so we’ll arrange for all the planet’s Muslims to jump off a…aw, never mind. I don’t have any kids (vasectomy,) so I’m nobody’s ancestor.

“I’m all right, Jack. Screw you all.”–Anthony Newley, probably quoting somebody else