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-   -   Moving Earth out of orbit (https://boards.straightdope.com/sdmb/showthread.php?t=795574)

Jonathan Chance 06-12-2016 12:42 PM

Moving Earth out of orbit
 
OK, so this has happened in fiction a number of times. It's shown having various effects with Earth wandering through space, getting too close to the sun, whatever. This is not the concern of my friend and I right now.

What would it take to do so? In the fictitious version Earth always appears to just quietly go on its merry way. But I'm asserting that the power needed to do so is such that it would cause the Earth to lose cohesion and fall apart like the asteroid belt. The earthquakes alone would wipe out most life.

So what's the scoop? Is there a way to move a planet out of an orbit without destroying it in the process?

Exapno Mapcase 06-12-2016 12:52 PM

Sure. Just do it very, very slowly.

Quartz 06-12-2016 12:52 PM

Easily. Remember Newton's Laws of Motion. You just need a nearby stellar-mass object close enough and in the right position to negate the gravitational attraction of the sun.

eburacum45 06-12-2016 01:06 PM

The late Paul Birch of the British Interplanetary Society described one possibility in some detail here
http://www.orionsarm.com/fm_store/MoveAPlanet.pdf
In short, you send a stream of iron pellets made from asteroids between a ring of electromagnets in orbit around the Earth and another ring around a larger object (usually the Sun) which acts as an anchor. The force used to deflect these pellets will act on the Earth (and to a lesser extent on the anchor object) and gradually move them both with respect to each other.

Birch was primarily concerned with moving Venus, but the same technique could be used on Earth.

Stranger On A Train 06-12-2016 01:19 PM

Quote:

Originally Posted by Quartz (Post 19399313)
Easily. Remember Newton's Laws of Motion. You just need a nearby stellar-mass object close enough and in the right position to negate the gravitational attraction of the sun.

Except remember those pesky forces that create tides in the ocean and cause the crust to flex? Now you've added another. Even the relaxation of stored potential energy in the crust will have dramatic effects on tectonics. Not perhaps world destroying, but enough to create mass earthquakes, tsunamis, and increased volcanism. And any effort to apply force directly to the crust (e.g. a rocket extending outside the atmosphere or some similar direct thrust structure) will cause dramatic effects. The Earth's crust is proportionally much thinner and weaker than an eggshell, and even a thrust structure many tens of miles in diameter would be like a pinhead on the surface.

The Birch proposal outlined by eburacum45 is probably most practical, for generous values of "practical", but realistically the amount of energy required to move the planet from its orbit is vastly beyond anything we can produce today. That's how strong gravity is, and we don't even have to pay a monthly bill for it. Amazing stuff.

Stranger

burpo the wonder mutt 06-12-2016 01:34 PM

Couldn't you just tip it perpendicular, so we could have bands of weather consistent year-round? Please? I'll give you a dollar.

Riemann 06-12-2016 01:43 PM

Quote:

Originally Posted by burpo the wonder mutt (Post 19399408)
Couldn't you just tip it perpendicular, so we could have bands of weather consistent year-round? Please? I'll give you a dollar.

Nobody likes to buried under 6 feet of snow on short notice, but let's not get carried away here. I'll bid $2 to keep the changing seasons, please.

bob++ 06-12-2016 01:52 PM

Maybe you guys don't appreciate what a knife edge we live on, here on our little planet. Move us a few thousand kilometres nearer or further from the sun and we roast or freeze; alter the ecliptic angle and who knows what would happen to the tide, currents and weather fronts. Speed up or slow down the rotation speed and all that engineering based on one G would mean nothing.

Entropy will take care of it all - eventually.

Stranger On A Train 06-12-2016 02:35 PM

Quote:

Originally Posted by bob++ (Post 19399452)
Maybe you guys don't appreciate what a knife edge we live on, here on our little planet. Move us a few thousand kilometres nearer or further from the sun and we roast or freeze; alter the ecliptic angle and who knows what would happen to the tide, currents and weather fronts. Speed up or slow down the rotation speed and all that engineering based on one G would mean nothing.

Well, it's not all that sensitive. The Earth varies in distance to the Sun of a few million kilometer through its not-quite-circular orbit (e~0.016) and has probably bobbled a few degrees off of its current 23.4 inclination to the solar ecliptic throughout the existance of life. (The rotation speed has almost no influence on felt acceleration; we do recalculate weight for large rockets between mid-latitude depot and near-equiatorial launch site, but the resulting difference is generally about a few dozen pounds for a several tens-of-thousands of propellant grain mass motor. On a personal level, you won't notice or care.

However, changes in diurnal rythyms may be problematic for various species, especially intertidal sealife, but that's a lifestyle problem. I think we're better off leaving the Earth as it is and creating our own habitats in space which we can construct and operate on whatever cycles we like, but of course that is too simple a plan.

Stranger

eburacum45 06-12-2016 03:13 PM

Probably the biggest effect on a planet with a faster rotation would be more dramatic wind patterns; hurricanes, cyclones and anticyclones would rotate faster, and so on. Having a greater axial tilt would also cause more dramatic and more seasonal weather, although (according to some simulations I've seen) a planet with a greater tilt would probably have smaller ice caps or none at all. None of this would make life impossible, as far as I can see.

Mangetout 06-12-2016 04:17 PM

Quote:

Originally Posted by Stranger On A Train (Post 19399555)
Well, it's not all that sensitive. The Earth varies in distance to the Sun of a few million kilometer through its not-quite-circular orbit

Variation in the orbit doesn't necessarily indicate lack of sensitivity

What matters is probably not the momentary condition, but the average of all the various states. Sure, the distance between the earth and sun varies throughout the year, but if you move the earth so that on average, it's a few million kilometers closer or further away than the current average, we might run into trouble.

Senegoid 06-12-2016 04:29 PM

You need but a long enough lever and a place to stand.

(Well, you need a fulcrum too. Maybe you can use the moon, or maybe Mars, for that.)

robby 06-12-2016 04:52 PM

Another related option that has been studied is the possibility of using a large asteroid in a gravity assist maneuver to transfer orbital energy from the outer planets to Earth in order to expand Earth's orbit.

Estimates are that it would take thousands of gravity assists to make a difference. And a screw-up that results in the asteroid impacting the Earth would be catastrophic, to say the least. But if the alternative is the oceans' boiling away as the Sun expands, we may have no choice but to try it, assuming we develop the capability.

Article about one such plan here:
http://io9.gizmodo.com/5923828/dont-...ving-the-earth

Vicsage 06-12-2016 04:53 PM

Change the gravitational constant of the universe, thereby altering the mass of the Earth.

Stranger On A Train 06-12-2016 05:12 PM

Quote:

Originally Posted by Mangetout (Post 19399808)
Variation in the orbit doesn't necessarily indicate lack of sensitivity

What matters is probably not the momentary condition, but the average of all the various states. Sure, the distance between the earth and sun varies throughout the year, but if you move the earth so that on average, it's a few million kilometers closer or further away than the current average, we might run into trouble.

"...a few thousand kilometres nearer or further from the sun" is not going to significantly change the thermodynamic state of the Earth, and even a few million is not going to make the planet uninhabitable. The sun goes through phases in variation of irradiance and temperature.

Stranger

bob++ 06-12-2016 07:23 PM

Yet we worry about a couple of degrees of global warming?

burpo the wonder mutt 06-12-2016 07:40 PM

Quote:

Originally Posted by Riemann (Post 19399431)
Nobody likes to buried under 6 feet of snow on short notice, but let's not get carried away here. I'll bid $2 to keep the changing seasons, please.

Seasons suck! Raising my bid to 3 whole dollars. ;)

Chronos 06-12-2016 07:58 PM

There's a vast gulf between "catastrophic" and "uninhabitable". If global warming were to kill off, say, 5% of the humans on the planet, we'd consider that abominable, but by most species' standards, 95% survival is thriving.

DagNation 06-12-2016 09:40 PM

Quote:

Originally Posted by robby (Post 19399885)
Another related option that has been studied is the possibility of using a large asteroid in a gravity assist maneuver to transfer orbital energy from the outer planets to Earth in order to expand Earth's orbit.

Estimates are that it would take thousands of gravity assists to make a difference.

This is the easiest answer - most of the energy comes from the large outer planets, a tiny fraction comes from maneuvering thrusters that align the trajectories and make it work right.

Assuming the goal is to gently raise the orbit of earth to counterbalance the rising output of an aging sun, an increase of average orbital radius of a million miles over a hundred or thousand years is going to be enough to do the job, and do it very gently in terms of tidal affects on the surface.

I think a major challenge would be to do it without messing up the moon's orbit.

As long at we have massive rocket-powered asteroids transferring all that orbital energy around, it would be difficult to not effect the other planets, so might as well make use of it all. It would be fun to grab Mercury, Venus, and Mars, and put them in orbits at earth's L-points.

It would be nice to move the other rocky planets because it would be a lot easier to terraform them if they were in our Goldilocks orbit and had the same solar input.

Jonathan Chance 06-12-2016 10:07 PM

Two things:

1. What is the amount of energy required to move the Earth in such a manner?

2. Would the sun losing mass lower its gravity and therefore slip Earth into a wide orbit in the first place?

Grey 06-12-2016 10:20 PM

Quote:

Originally Posted by bob++ (Post 19400202)
Yet we worry about a couple of degrees of global warming?

No, we worry about a global energy equilibrium being rapidly moved in a single direction.

Mangetout 06-13-2016 02:03 AM

Quote:

Originally Posted by Stranger On A Train (Post 19399938)
"...a few thousand kilometres nearer or further from the sun" is not going to significantly change the thermodynamic state of the Earth, and even a few million is not going to make the planet uninhabitable. The sun goes through phases in variation of irradiance and temperature.

Stranger

Do those phases oscillate about some sort of consistent mean?

Isilder 06-13-2016 02:20 AM

Quote:

Originally Posted by Jonathan Chance (Post 19400496)
Two things:

1. What is the amount of energy required to move the Earth in such a manner?

The escape velocity at earth's distance is about 42 km/second

From https://en.wikipedia.org/wiki/Escape...ape_velocities

The earth is currently at 30 km/sec


The cheapest way is to boost the earths mass up 12 km/second pro-grade (directly in the line of the orbit - actually instantaneous pro-grade.. as you apply the acceleration you keep it in the actual direction of movement. ) .. Its more expensive to do it by applying the force in some other direction than pro-grade...


Your other question sure reduce the mass of the sun to make the escape velocity (kinetic energy) lesser.. changes the orbit of the earth too

eburacum45 06-13-2016 05:18 AM

When the Sun leaves the Main sequence it will star losing mass comparatively rapidly, due to a vastly increased solar wind. Some estimates say that this loss will be enough to move the Earth's orbit out beyond the edge of the Sun's red giant phase; others aren't so sure.
http://www.astronomy.ohio-state.edu/.../vistas97.html

Quartz 06-13-2016 05:41 AM

Quote:

Originally Posted by eburacum45 (Post 19400962)
When the Sun leaves the Main sequence it will star losing mass comparatively rapidly, due to a vastly increased solar wind. Some estimates say that this loss will be enough to move the Earth's orbit out beyond the edge of the Sun's red giant phase; others aren't so sure.
http://www.astronomy.ohio-state.edu/.../vistas97.html

By that stage the Earth will have lost its magnetic field due to cooling of the core, so it may no longer have an atmosphere.

Blue Blistering Barnacle 06-13-2016 12:13 PM

Quote:

Originally Posted by Quartz (Post 19400981)
By that stage the Earth will have lost its magnetic field due to cooling of the core, so it may no longer have an atmosphere.

Well, that would take care of the "season's issue". You should collect $3. :)

XT 06-13-2016 01:59 PM

[QUOTE=Jonathan Chance;19400496]Two things:

1. What is the amount of energy required to move the Earth in such a manner?


From here:

Quote:

The escape velocity from the Sun at the vicinity of the Earth is about 42 kilometers per second. You need to subtract the Earth's orbital velocity from that (assuming you push in the direction the Earth is already travelling to save energy). So the energy needed to accelerate the Earth up to escape velocity from the Sun is:

4.4571032J

(joules) - see (Wolfram Alpha calculation)


To understand this huge number, let's convert it to some other forms:

It is 13.4 days

of the Total Solar Energy output - see (Wolfram Alpha calculation)
and is the energy obtained if you convert 51015 kg
(kilograms) of mass to energy - see (Wolfram Alpha calculation)
To understand this huge mass, it is equivalent to the mass of the all the humans on the planet Earth times 10,000
- see (Wolfram Alpha calculation)
I suppose if you were working very long time scales and could engineer some sort of mass that would stay at a constant distance from the Earth you could, eventually, shift the orbit outward...but we'd probably be talking millions of years (or 10's of millions of years), and today there is no practical way to even start working on something like that....especially if we were wanting to live through the experience.

eburacum45 06-13-2016 04:43 PM

Note that you wouldn't have to accelerate the Earth to escape velocity in order to move it outwards by a few miilion kilometres. Although the energy required would still be vast.

According to current theories the ice ages on our planet are significantly affected by minor changes in the eccentricity of our orbit; changing the shape of our orbit artificially would certainly cause some very significant changes in our climate.

dtilque 06-13-2016 05:08 PM

Quote:

Originally Posted by Jonathan Chance (Post 19400496)
2. Would the sun losing mass lower its gravity and therefore slip Earth into a wide orbit in the first place?

This is happening right now, but the rate of solar mass loss is so low that it's pretty negligable. AIUI, the Earth is currently moving away from the Sun about 15 cm/year, but most of that is due to tidal drag.

Gilbert1984 06-15-2016 06:36 AM

Quote:

Originally Posted by Senegoid (Post 19399839)
You need but a long enough lever and a place to stand.

(Well, you need a fulcrum too. Maybe you can use the moon, or maybe Mars, for that.)

Obligatory - possobly NSFW, definitely Not Safe For Humanity

http://zase.mk/wp-content/uploads/20...-Miami-061.jpg

Chronos 06-15-2016 06:55 AM

...I fail to see the relevance of that image to anything in the quoted post or to the thread in general.

Quartz 06-15-2016 07:35 AM

There used to be a website that showed the effect of a passing star on the inner planets. I can't find it now.

Leo Bloom 06-15-2016 09:13 AM

Quote:

Originally Posted by dtilque (Post 19402534)
This is happening right now, but the rate of solar mass loss is so low that it's pretty negligable. AIUI, the Earth is currently moving away from the Sun about 15 cm/year, but most of that is due to tidal drag.

How is this made manifest in the elliptical orbit?

Andy L 06-15-2016 11:16 AM

Quote:

Originally Posted by Quartz (Post 19406586)
There used to be a website that showed the effect of a passing star on the inner planets. I can't find it now.

This one http://janus.astro.umd.edu/orbits/nbdy/rstar.html ?

dtilque 06-15-2016 06:40 PM

Quote:

Originally Posted by Leo Bloom (Post 19406755)
How is this made manifest in the elliptical orbit?

Not really sure. The annual increase (15 cm/year) was calculated by a couple Russians (Gregoriy A. Krasinsky and Victor A. Brumberg) using (I think) timing of comunications to interplanetary probes. This paper says that it is probably due to tidal drag. I'm going to guess that it mainly shows up in a change in the semi-major axis.

Blue Blistering Barnacle 06-15-2016 06:43 PM

Quote:

Originally Posted by dtilque (Post 19408298)
Not really sure. The annual increase (15 cm/year) was calculated by a couple Russians (Gregoriy A. Krasinsky and Victor A. Brumberg) using (I think) timing of comunications to interplanetary probes. This paper says that it is probably due to tidal drag. I'm going to guess that it mainly shows up in a change in the semi-major axis.


Semi-major- does that mean the orbit becomes more elliptical with time?

dtilque 06-15-2016 07:51 PM

Quote:

Originally Posted by Blue Blistering Barnacle (Post 19408310)
Semi-major- does that mean the orbit becomes more elliptical with time?

It would if my guess were right. But after thinking it over, I realized that it's wrong. Since tidal drag is a slow continuous process, it should show up as an increase everywhere along the orbit.


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