How would "Fixing" Venus and Mars effect Earths orbit?

[Crossroads Inc.]

Ok, so from time to time we have had various 'god' threads, and sooner or later someone says:
"HEY! I know what would be a good idea, I'll 'fix' Venus and Mars to make them habitable!"

Well, thats great, but fixing them, one would imagine would involve changing orbits. Venus is overcooked, and would have to be moved farther from the Sun, and Mars would have to be moved closer.

So the question is, if you changed the orbits of Venus and Mars so they would be in the habitable zone, how owuld that effect Earth, if at all? Would the change screw us over? Or would it perhaps only slightly change our own climate?

[Rabid]

Mars is already more or less on the edge of the habitable zone. If you had god powers, you would only need to make her bigger (to increase her surface gravity from 0.376 to ~0.5 G), and give her a big metallic core like Earth's one in order for her to generate a Magnetic Field that'll help her keep the atmosphere you'll give to it. Sure, it'll still be a bit chilly, not quite earthlike, but with the good atmosphere mix you could easily reach a 5°C mean temperature.

Venus, in the other hand, is just a few millions kilometers too close to the sun (orbiting at roughly 108 million kilometers from it). You'd want it to be something like ten to twenty million kilometers farther from the sun, in order to be comfortable enough ; but then the resonance cycle between Venus and Earth would be different, and I don't know what would be the long term impact on the dynamic of the solar system.
Once it's done, it would mostly be a matter of changing the atmosphere, methink.

[Number Theoretic]

Sounds to me like a multibody problem with more than three bodies, so there is no analytical solution and you definitely need to simulate it (i.e. integrate it numerially) to see what is happening. I didn't find a online multibody physics simulator on the quick, but perhaps this orbit parameter applet can be a starting point. If you find a simulator that requires extensive orbit parameters (or implement one yourself) as input, the above link can come in handy.

[Lord of the Abyss]

Mars is already more or less on the edge of the habitable zone. If you had god powers, you would only need to make her bigger (to increase her surface gravity from 0.376 to ~0.5 G), and give her a big metallic core like Earth's one in order for her to generate a Magnetic Field that'll help her keep the atmosphere you'll give to it. Sure, it'll still be a bit chilly, not quite earthlike, but with the good atmosphere mix you could easily reach a 5°C mean temperature.

Mars still has a problem though. without a large moon, it's vulnerable to axis tipping; and with a molten metal interior to generate a magnetic field it's vulnerable to the crust sliding around on the liquid interior. I've read that that in fact appears to happened in Martian prehistory; when volcanic activity built up a mass concentration of dense rock in a region, the crust slid so the mass concentration was at the equator. A large moon prevents that sorts of thing due to tidal forces and angular momentum.

So, with god-powers it seems to me you could kill two birds with one stone and move Venus out to Mars and set them up as a double planet. Venus is cooler, and the new Mars/Venus system us much more stable like the Earth/Moon one is. It's even better if you can move them in a little towards the Sun without screwing up Earth's orbit, of course.

Another possibility would be to give Mars Earth's moon, and install Venus as a double planet with Earth in its place.

[Simon_Jester]

I'm not sure any of this would really be necessary. On human-meaningful timescales (say, a few million years), I would think you could give Mars and Venus stable biospheres without changing their orbits materially.

Moreover, if you had the technology to move planets in their orbits, you could just correct any perturbation to the Earth's orbit caused by the displacement of the planets- indeed, this would probably be a lot easier to do than moving planets in the first place.

[B5B7]

The problem with Venus is not its distance from the sun - it is at a distance where it is quite possible it could have been a relatively pleasant planet. What happened is that at some stage a process started that trapped heat on the planet, and a positive feedback occurred heating the planet even more.
Even if doubled its distance from the sun, the heat would still be trapped on Venus, by its atmosphere. Much of the heat comes from within Venus from geological processes.

If a race has the tech to move worlds, then they probably have some better means to cool Venus.

[Stofsk]

Venus isn't going to become habitable simply by moving it into another orbit. It's not just the heat but also the atmosphere, it's chemical composition and pressure, everything. Venus is the closest thing to hell that actually exists in nature.

As for Mars, well if it needs a moon couldn't you get a particularly large asteroid and use that? Phobos and Deimos are captured asteroids after all, albeit tiny ones.

[Patrick Degan]

For Venus, you need a lot less to move the planet to a different orbit and a lot more to scoop off about 90% of its present atmosphere to make terraforming possible.

[Guardsman Bass]

Several of the outer solar system moons are close to the Moon's mass as well. If you've got amazing planet-mover skills, you could maneuver one of them into the Inner Solar System and put it in orbit around Big Mars (or re-located Venus).

As for Venus, you could presumably use your Planet Mover capabilities to ship off most of Venus's atmosphere in the process.

[Silvertongue]

As for Venus, you could presumably use your Planet Mover capabilities to ship off most of Venus's atmosphere in the process.

Maybe we blow off the extra atmosphere by smacking Venus with a few comets (or RKVs), and possible do triple duty of fixing it's rotation and orbit?

We might have to follow up with other means to cool, move, and rotate the planet, but this sounds like a good start.

[Simon_Jester]

Its orbit doesn't need fixing. Its rotation probably would, because it's practically tide-locked: the day/night cycle is 240 days long or so. Between that and how close it is to the sun, it might be very difficult to terraform the place even if you could fix the atmosphere, because any given spot on the planet experiences four months of really intense sunlight, about twice what you get on Earth, followed by four months of total darkness.

[starslayer]

Venus has retrograde rotation and a prograde orbit, so the solar day is actually "only" about 117 days. Still potentially a big problem for temperature control, but less than its sidereal day might suggest.

[fnord]

How quickly would decreasing solar insolation (either via sunshade, moving planet further out, etc) act to reduce Venus' temperatures on its own? I'm guessing not too quickly due to the greenhouse effect currently in place, but I have no idea on an actual timescale.

[Ariphaos]

In a previous thread on this I mentioned 'fixing' Venus in one go by dropping two large dwarf planets on it (prolly not Pluto, but bigger things that are no doubt further out). You shift the orbit, create a moon, clean off the atmosphere, and help its rotation (probably not enough, but every journey of a thousand miles begins with a single step and all that). Put up a sunscreen to speed up its cooling, then begin terraforming after a millennia or so.

I don't think the low mass of Mars is exactly a short term problem. If it bothers you, bulk up Ceres a bit and pull it into its orbit.

[madd0ct0r]

nah, if we've got that kind of chucking planets about ability, just swap venus and mars in position.

[Simon_Jester]

Really, Venus's position is fine, and stripping away its atmosphere really should be comically easier from an energy-momentum standpoint than moving around hundred-kilometer asteroids. It's not that Venus is too close to the sun for life, or that moving it would be all that helpful (since the horrible atmosphere doesn't go away immediately). Speeding up its rotation would be good (and difficult, obviously), but moving its orbit is just... I don't think there's any payoff that justifies the colossal investment in resources you'd need to make it happen, assuming you could do it at all on anything less than geologic timescales.

Besides, it occurs to me that moving Venus without stripping the atmosphere might be a problem, just because of the difficulty of setting up equipment on the surface.

Venus has retrograde rotation and a prograde orbit, so the solar day is actually "only" about 117 days. Still potentially a big problem for temperature control, but less than its sidereal day might suggest.

It's not just temperature control that's the issue, it's a biosphere- if you really want to terraform the place, you have to change the day/night cycle or breed plants that can survive alternating between months of intense sunlight and months of absolute darkness.

Otherwise, about the best you could do, I think, would be to strip off the atmosphere entirely and turn it into a bigger version of the moon- in which case you could build subterranean dome-habitats and so on.

[Patrick Degan]

As for Venus, you could presumably use your Planet Mover capabilities to ship off most of Venus's atmosphere in the process.

Maybe we blow off the extra atmosphere by smacking Venus with a few comets (or RKVs), and possible do triple duty of fixing it's rotation and orbit?

We might have to follow up with other means to cool, move, and rotate the planet, but this sounds like a good start.

With a technology up to that level (where moving large bodies would seem feasible), it would also seem feasible to construct 1000 km focusing lenses and mirrors to place in position to boil away the excess atmosphere of Venus. The project would achieve the same aim with far less effort involved than actually shifting worlds out of their orbits —a contingency I would reserve for the time when the sun starts acting up.

[Crossroads Inc.]

And this is why I love SD.Net.
You pose a question expecting one answer, and you come up with solutions you didn't even think possible.
The fact that it seems Venus can be "fixed" just by altering its Atmosphere, and not needing to change the orbit at all was something i had not even considered.

[Surlethe]

So why don't we build some giant mirrors to boil off 90% of Venus' atmosphere, drop a passing comet on it to start the oceans, and then position the mirrors as dual sunshades/mirrors to even out the day-night cycle?

(PS- What the hell is "axis tipping"? The only way you can tip the axis of a planet is by dropping a moon on it or maybe via long-range tidal interactions with the sun.)

[Guardsman Bass]

I thought Venus's orbit was inside the habitable zone of the Sun, and that "merely" giving it regular days, oceans, and an Earth-like atmosphere would still leave it extremely prone to runaway greenhouse effects due to the much greater solar insolation. You could obviously mitigate that with your giant mirrors/sunshades, but then the entire biosphere is dependent on your active management.

[Simon_Jester]

Hmmm. I wonder if you could tilt an axis of rotation- if you could apply enough lateral force to certain points on the planet for a long enough period of time, timed correctly. It would be prohibitively difficult, though- but physically possible if you just had enough torque.

Or if you were trying to impart rotation to the planet (speed up its day), you could simply apply the torque intended to do that about an axis different from the axis of the existing rotation- by the time you've spun the planet up to have something like a 24-hour day/night cycle, the original rotation of the planet will be noticeable only as a tiny little wobble.

But if you aren't in a position to materially shift the motion of a planet, and realistically you aren't, then no, there's really not a lot that can be done for Venus that way.

I thought Venus's orbit was inside the habitable zone of the Sun, and that "merely" giving it regular days, oceans, and an Earth-like atmosphere would still leave it extremely prone to runaway greenhouse effects due to the much greater solar insolation. You could obviously mitigate that with your giant mirrors/sunshades, but then the entire biosphere is dependent on your active management.

Giant sunshades are pretty easy to manage- you just place physically large objects in orbit around the planet, and they will stay there if you do it right. Also, for terraforming purposes you're really more concerned with making the place habitable with your own people on it- doing a billion times more work to give it a stable biosphere in the event that your civilization collapses probably isn't worth it.

Hmmmm.

I suspect it would also help to encourage lots of water vapor in the Venusian atmosphere, so as to reflect sunlight- ironically, this is what most astronomers thought Venus was like before we got hard data on the place in the '60s. Hence the "swamps of Venus" presented in a good deal of mid-20th century fiction.

Also, if you have sunshades, you can place sunshades and mirrors in an orbit around the planet Venus such that they circle the planet every 24 hours- or maybe a little longer. That might create a 'virtual' day/night cycle, although you'd run into problems with tidal shear if the sunshades are large enough to be useful.

[eion]

Most of the Venus terraforming ideas I've read suggest ejecting the excess atmosphere in a consistent direction, i.e. like a rocket engine. Not only does this rid you of the excess atmosphere, but it speeds up Venus' day, probably not to anything like an Earth solar day, but something more like a solar day on the Moon, a few weeks or so.

As for needing a molten core on Mars to create a magnetic field, I would only point out that we can create far stronger magnetic fields with far simpler technology ourselves and it would probably be far simpler to use orbiting magnetic sails and city-covering magnetic field generators along with insulated houses to achieve the same effect far more cheaply and quickly.

Mars' size is also not a big issue in the near-term (and by near term I mean thousands of years at least), as any atmosphere we introduced would last at least that long with no maintenance.

[Lord of the Abyss]

(PS- What the hell is "axis tipping"? The only way you can tip the axis of a planet is by dropping a moon on it or maybe via long-range tidal interactions with the sun.)

Or by mass building up (such as a large mountain range) away from the equator; centrifugal force will then tend to tilt the planet or drag the crust over the molten interior. That's one reason why a large moon like our stabilizes Earth; the tidal bulge ensures that the equator always has extra mass.

[FedRebel]

Ok, so from time to time we have had various 'god' threads, and sooner or later someone says:
"HEY! I know what would be a good idea, I'll 'fix' Venus and Mars to make them habitable!"

In my view we can't have both, since Venus is closer in size to Earth and Mars is too small to maintain a breathable atmosphere, Mars is going to have to go.

By that I mean it's orbit would be altered to smack into Venus just right (that 'sweet spot' that'll create a stable large satellite)

With the atmosphere blown off from the impact, that solves that problem. Once Venus cools enough, we smack several hundred comets into it to give it plenty of water and nudge the post impact atmosphere to a point where we can seed it with plants.

Outside of some fine tuning (i.e. reinforcing the Ozone layer) we can begin settlement, in what, a thousand years give or take (being extremely liberal)

[Surlethe]

(PS- What the hell is "axis tipping"? The only way you can tip the axis of a planet is by dropping a moon on it or maybe via long-range tidal interactions with the sun.)

Or by mass building up (such as a large mountain range) away from the equator; centrifugal force will then tend to tilt the planet or drag the crust over the molten interior. That's one reason why a large moon like our stabilizes Earth; the tidal bulge ensures that the equator always has extra mass.

How? In a closed system, angular momentum is conserved, which means that the axis of rotation has to remain the same. There is no geological process that could possibly cause the Earth to tilt on its axis (save an Io-like volcanic ejection of mass); that would be like pulling yourself up by your own bootstraps.