New Mars Forums

Okay, so liquid water is a better heat sink than water vapour. How do you get liquid water on Venus? By precipitating it out of the atmosphere. How do you precipitate it out of the atmosphere? By dropping it from clouds. How do you get the clouds? By cooling the planet. How do you cool the planet? By making clouds. Can you see the problem here??

The issue on Venus s reversing the greenhouse, just as on Mars the issue is triggering the greenhouse. Any rain that fell from clouds on Venus would never hit the ground -- it would evaporate at about the 40-50km height. How much water would be needed to get this going? Would all the water on Europa be sufficient? Or Chiron or one of the other centaurs?

Bryan

Would it truly need to be so big? Luna changed the rotation of Earth without being the size of the Earth. We know that, at the time cyanobacteria were laying down mats in our young oceans over 500 Mya, because these mats grow one layer per day, thus making rings like tree rings, that the year had more than 450 days in it. But our orbit around the Sun was approximately the same. Therefore there were the same number of hours in a year, but fewer hours per day because Earth rotated faster. Luna has receded thousands of miles since then and the tidal friction has slowed down Earth's rotation.

I am asking these questions about angular momentum because I have read so many posts on here by people proposing to create moons for Mars or Venus with the goal of affecting angular momentum of the planet. My (limited) understanding of physics suggests to me that this will not work. But I am intrigued by the possibility, so I am trying to goad people into debating this thoughtfully to see if there is any substance to the dream at all.

What effects would a massive moon have on a planet? Would a moon just outside the Roche Limit have greater umphh than a more distant one? The tidal friction would generate heat, in both objects. What else?

Bryan

nickname --

I see today that you were trying to say the same thing I was, but I didn't get the explanation -- yes, 1 bar on Mars is not 0.333 bar just because it is 0.333 gravity, but actually maybe 0.5-0.6 bar because the mass of the gas is more confined at the bottom of the column.

Maybe 0.5 bar in the southern hemisphere and 0.6 bar in the northern. Maybe 0.7 bar in the canyon depths.

By the way -- hello to London. My mother was born there. I am in Kitchener.

Bryan

I know Ceres is spherical (at about these dimensions), but aren't Pallas and
Vesta nearly so as well, at about half the size. Even so, yes, a lot of matter.
Maybe if we include some FeNi and some plutonium it will heat up.

What do you mean by "do work on the solar wind"? Are you making the distinction
between an induced magnetic field versus a permanent magnet? What is the
functional difference? I understand that some (all?) of the Jovian moons have
induced magnetic fields because of their orbits within Jupiter's magnetosphere.
Does this mean that if you took a moon out of Jupiter's gravity well that it
would lose its magnetic field? How does one make a permanent magnet??

Would a magnetised moon be "highly desirable" for the longterm viability
of terraformation? Or merely "window dressing"?

Venus has only the faintest of magnetic fields, but I'm not sure why this has
come about. Surely it has a molten core?? It has a molten surface! But liquid
metal should generate some magnetic dynamics, yes? Or is it so weak because of
its retrograde rotation? I wonder if Venus got a retrograde rotation by being
knocked upside down, in effect? I gather that Uranus has its north pole below
the ecliptic and its south pole above the ecliptic, meaning that it got knocked
over beyond just 90*. Venus may be exhibiting its original rotation, but if its
physical poles have fully reversed, then it would end up rotating in reverse.

Ahaaa! Yes, and this was my biggest question. Does the "help" change depending
upon the process used to acquire the moon? I see a lot of people on here talking
about lifting mass (carbon from Venus for ex) and putting it into orbit. But lifting
mass changes the angular momentum of the planet it is being lifted from. If energy
can be neither created nor destroyed in a closed system, then how does lifting matter
into orbit actually help?? I'm trying to work out whether taking matter off
one side of the ledger and adding it to the other side of the ledger actually improves
the conditions on the first side of the ledger or if it is all a zero-sum game and
ultimately pointless.

Do Phobos and Deimos contribute more than marginally to the stability of Mars? Does
the swarm of satellites buzzing around Earth affect our own orbital dynamics? (We have
lifted mass and put it into orbit!)

If we did create a moon for Venus, should it revolve in the "normal" manner or in
keeping with the retrograde rotation of the planet itself? Which manner will lead it
to increase its distance over time and which manner will lead it to fall into the Roche
Limit and be destroyed, a la Triton at Neptune or Deimos at Mars?

Not the L1 point within the Earth-Moon system -- I mean the L1 between
the binary Earth-Moon system and the Sun. Because the barycenter is within the Earth's
crust or mantle, but the Moon is receding, L1 to the Sun must also be receding, because
the total diameter of Earth-Moon (the Moon's orbit) is expanding. But because the centre
of mass (barycenter) is so remote from the system perimeter (outward lunar surface),
I think the distance from the Moon to the Solar L1 must be getting compressed over time.
Could L1 approach or intersect the Moon at perihelion?

Magnetic axis, not magnetic angle. On Earth, yes, the magnetic axis and the rotational
axis are not at identical angles, but both intersect at the geometric centre of Earth.
What I am saying about Uranus is that its magnetic axis does not bisect the planet into
two equal halves -- its centre is off-centre, geometrically. It's a chord.

Standard theory today regarding the creation of the Moon is that an impactor
the size of Mars collided with Earth after stratification of the core had already
taken place. This impactor is named Theia and it occupied L5 in Earth's own orbital
path. It was a competitor in the race to "clear the orbit", as the IAU would have it.

A natural breeder reactor in the Congo ?? Okay -- spill! :-)

Bryan

Am I right in thinking that one bar of atm on Mars is less gas than one bar on Venus or on Earth? Because it is a smaller planet ... Therefore it just takes less gas to achieve one bar of pressure at the surface. And do we know how much less gas this means? And are we taking this into consideration in calculations of time estimates, etc.?

Bryan

I have seen many proposals on here for giving either Mars or Venus a moon and also for tweaking the nagular momentum of the planet or else reigniting the internal planetary dynamo. I am uncertain of the physics of this and suspect there may be rather severe constraints on what we should even consider hoping to achieve.

Let's explore this. Here are some options:
1) Parking NEA, NVA or NMA (asteroids) into orbit.
2) Lifting mass off the planet surface to make a moon. Mostly proposed for Venus only.
3) Lobbing iron-nickel impactors at our neighbours and also incidentally cleaning up the terrestrial neighbourhood.

And now here are the concerns for each:
1) Can we move a mass the size of an asteroid both with the speed and the precision to bring it into orbit around another body? This means both overcoming its initial inertia and orbital mechanics and then braking imparted inertia to bring about orbit?
a) As a subset of this method, would it be feasible to accrete matter onto either Phobos or Deimos? They are, after all, already in orbits and that is the most difficult part of the whole enterprise.
b) What is the mass of these sets of asteroids available for moon-building? Are there enough NVAs to create a satellite with enough gravity to form itself into a sphere? Likewise with the NMAs? Perhaps more with Mars than with Venus. I'd like to pair up Eros with Venus ....   

2) Can we build a moon from scratch, a la Death Star fashion? I would not want to attempt this with Mars, but I have seen several proposals on here for Venus, as a depository for excess carbon. I'd rather see it take excess sulphur personally, but let's play with this. You'd want to begin with a hollow iron sphere positioned in orbit. Perhaps magnetise the whole sphere to encourage passive accretion by space dust? Or would solar energy rob it of its field? Could we lift enough carbon and sulphur out of the Venus gravity well to make this work? At what point would there be enough matter on the surface of this moon to shield the hollow core from solar radiation and other interference? If it could be shielded, then a metallic magnetised core could be built inside.

3) Lobbing impactors at planets is the cheapest way to add energy into a planetary system, but the process is inherently chaotic and we cannot know all the consequences of our actions in advance. After all, it was impactors on Mars which brought pieces of Mars to our Antarctica. And impactors on Luna send bits of moonrock down here to us. I'm guessing impactors on Venus might have consequences only for Mercury, but can we be sure? Impactors affect angular momentum, but do not create moons, unless we are talking about Velikovskian collisions.

Which brings us to the related topic of angular momentum. Does giving a planet a moon help angular momentum? I expect not, but perhaps there are better informed people on here.

Earth got its Moon out of a cataclysmic collision in the early solar system. The theory is that we had a Lagrange companion which accreted enough matter to lose its position and come towards us. Theorists name this object Theia, the mother of the Moon (Selena). Theia struck us a glancing blow which vaporised our crust and sent most of it into orbit. Theia was nearly the size of Mars. Theia is not the Moon -- Theia was engulfed into the Earth itself. But Earth had evolved sufficiently to have stratified into layers, with iron and nickel and uranium sinking into the core, while silicates floated on top. Theia blasted off the silicate layer and sent it into orbit. That is why the composition of the Moon nearly mirrors that of our crust, but it lacks the materials found in our deeper layers. Theia created the living Earth of today -- the surviving fragments of original crust became the cratons around which the continents congealed. It made plate tectonics possible. Pangea. Some of the oldest plates only fit together neatly if you increase the curvature of the surface (ie: if the whole planet is about 20% smaller). The Atlantic has opened and closed many times, but the Pacific has always existed -- this is where the crust was lost. Theia collided with Earth WITH the direction of rotation, thus giving our planet an extra spin. When the Moon coalesced above our Roche Limit, it became a DRAG on the angular momentum of Earth. It was the collision which imparted this angular momentum; it has been the Moon which has dissipated it ever since, through tidal friction. After Theia, the Earth had a day of 5-6 hours and a year of 1500+ days. When cyanobacteria mats were growing in our oceans, the rotation had slowed to 21hrs per day and 450 days per year. We know this because the fossil record preserves their growth rates of one layer per day. When Luna was born, it induced oceanic tides in excess of 300ft which washed over the whole planet while the bulk of the water stayed mounded up under the Moon. :shock: The Moon is still receding 10cm per year. The L1 point between the Earth-Moon system and the Sun is thus also gradually moving away, but I suspect not at the same rate. My suspicion is that the distance between Luna and L1 is slowly being compressed. I wonder if there will come a time in the far future when the radius of Luna will exceed the distance between its orbital path and L1? Then it could break free.

Late collisions of massive objects were a feature of the solar system in the first 100 Ma or so. Each orbit had more than one contender for dominance because accretion was happening everywhere at once. Ever wonder how Uranus got knocked over on its side? Or why its magnetic axis is off center from its geometric axis (ie: not tilted, but displaced -- not passing through the core)? It got knocked over.

Venus also experienced a late collision of cataclysmic proportions. Its orbital plane is slightly tilted to the solar ecliptic. It is not merely tidally locked to the Sun, but slightly retrograde. Venus got punched head-on by its Langrange companion. Consequently its energy was not added into the planet but subtracted. It got stopped nearly dead in its tracks. This depleted its full store of angular momentum. It engulfed its impactor. And the full thick silicate crust remained behind, which is another reason for the runaway greenhouse.

The bodies with the most angular momentum in the solar system are Jupiter first and Earth second. This gives us great orbital stability, like a gyroscope. If the matter on the Moon were to be returned to Earth in the direction of our rotation, then, indeed, like a skater bringing in her arms, we would spin like a top -- a day in five hours. As the inner planets accreted matter, their orbits walked outwards. Jupiter never budged. Consequently the matter in the asteroid belt got squeezed up against this immoveable object and could not pull it together.

Having said all this, I do not know how we can impart more angular momentum to Mars or Venus through use of a moon. The only way I can see is to use iron-nickel impactors aimed off-center with the direction of rotation. With Venus, even this may not work -- because its motion is retrograde, the planet would have to be slowed, stopped, reversed, to get it spinning in the right direction. And it would be *very* unstable. And it would add heat to Venus. :shock:

I'd like to ship all Earth's plutonium to Mars and drop it into the core. That would put starch in its sails.....

Bryan

As a species, as one multicellular lifeform among many in an ecosystem with billions of years of history at our backs, I do not believe that freedom from gravity is a realistic goal. We shall never be able to look back upon this blue dot in space and say Sayonara and make that stick. It may be a means to other ends, but it cannot be an end in itself.

For thousands of years on this Earth, sailors have heard the call of the sea and headed out into uncharted waters in search of new lands, but new land was always the goal. No seafaring people ever took to the sea and stayed there.

Having said that, there shall come a time when Space is thick with our vessels, plying the distances between the orbs of this solar system and perhaps beyond. Some vessels may drop anchor for a time to fish (mine asteroids) upon the high seas, but even they shall return to port.

Gravity wells are a necessary evil. The counterweight to the gravity problem is energy expended in getting in and out of gravity wells. I think a better focus would be on maximising the free energy provided by our Sun to get in and out of the wells and to quicken the transits.

Having said that, I think all the destinations under discussion here are high quality targets -- Venus, Mars, Moon, Europa, Callisto or Ganymede and Titan. Callisto because it is in the Jovian system but free of Jupiter's radiation belts; Ganymede because it has a magnetic field of its own and significant gravity (but still passes through Jupiter's radiation belts); both because they are proximate to Europa but are safer and gravitationally cheaper destinations.

I am trying to break down the problem into its constituent steps, in order to identify the first baby steps. What must come first?

There will be humans on Mars someday, but the climate is brutal, the surface conditions are brutal, the resources are poor -- I do not see where Mars is any more welcoming than the Moon and it is much further away. Look at how many missions to Mars tried to touch down gently and failed; then look at how many missions have relied upon lobbing an object at the surface and using ballistics to land it and succeeded. I think Mars lives up to its name in more ways than one. It is the god of war and we shall tame it only with harsh discipline, if at all.

I came to this site expecting to learn about Mars, but, along the way, in reading the posts here, I have instead fallen in love with Venus. I had never considered oxygen's potential as a lifting gas on Venus. That makes it all so much simpler. We never have to go down to the surface. Going to Venus means coasting in to land on a downy pillow. We can cope with that, as a species. Not every colonist will be a scientist and, even if, there is no guarantee that the offspring of a colony of scientists will match the calibre of the parents. In fact, our future growth off-Earth depends upon "normal" people getting out there. The planet is superabundant in the simple resources that we need to conquer others worlds -- solar energy, wind, oxygen, carbon, ... If Venus has 90atm at the surface and it is 5% nitrogen, then it must have more nitrogen than Earth. The gravity is comparable. People could step out onto the balcony on the cloudcity with an oxygen tank alone and not be concerned about temperatue control or pressure suits.

I think we must settle the Moon before we take on Mars -- airless, low gravity worlds present a certain set of challenges in common and we are not ready for them just yet. The Moon shall allow us to practise these skills close to home. When we get the Moon right, then Mars and Callisto and the asteroids shall be SO much easier. And, as a guiding principle, I firmly believe that we must conquer space with the resources of space. It will be wrong to rob this planet Earth of its resources in terraforming projects elsewhere.

Which brings us again to Venus. Venus has in abundance the resources that we want to take with us to the Moon and to Mars and elsewhere. At 50km up, its surface area is as great as the Earth. The jump from that altitude in and out of space is not as severe as from the surface -- the shuttles expend most of their fuel in that first 50km! Venus is a gift. Mars is hard work.

Again, what is the baby step? Before the cloud cities, there must be colonists and farms. Before the farms, there must be outposts. Before the manned outposts, there must be unmanned platforms and a diversity of self-sustaining experiments.

What would it take to float a fullerene bubble of algae and sulphur-eating bacteria at 50km on Venus? The fullerene bubble would fold up nicely like a parachute. The starter kit of water and algae and bacteria could be shipped in a 5 gallon jug. The floating mixture of air could be compressed in a tank. Send it all to Venus. Drop the bubble into the sky and let it inflate on its way down. Run the water and algae into the fullerene skin layer for maximum exposure to the Sun. The bacteria will convert the sulphuric acid into water and the algae will make oxygen and carbon. Richard Branson could get this much done!

Maybe the very first step is to send Venus a cargo of floating transponders and drop them into the atmosphere to watch how they behave in the winds, a la the movie Twister ...

Bryan

I value the summing up which launched this thread. That was very good, clear and concise. It brought the problems into sharp focus. We are all so focussed on Mars, yet the Venus cloudtops are looking like our best bet in terms of big results with little effort. I think that any project requiring massive mobilisation of resources right from Day One is going to be doomed to failure or else shall never be begun.

Colonising Mars (nevermind terraforming it) shall demand earthmoving equipment, explosives, smelters, domes, burrowing, heat, power sources, and much else which we just cannot yet do. Mars will demand an off-Earth infrastructure many orders of magnitude greater than what the ISS currently represents. I think Mars is a brutal place.

Venus on the other hand can be colonised without any need for immediate terraforming. People can begin living there a few colonists at a time in small self-sufficient colonies until a tipping point is reached. Terraforming will not, I believe, ultimately be directed from Earth, but shall come about on Venus under guidance from the colonists themselves as a natural evolution from their adaptation to the place. When they are ready, it shall begin, one small step at a time.

Having said that, I don't think we know enough yet about the chemistry of Venus (or Mars either, but I want to focus on Venus). The planet has come to this sad equilibrium for specific reasons. If we are serious about pushing it away from this equilibrium into a new equilibrium (and only an equilibrium will suffice -- constant effort and vigilance is an energy sink), then we have much to learn.

1) If we go the sunshade route, with intent to freeze out the CO2 onto the surface, then there will be no cloud cities. But Venus has no magnetic field, so we could see our remaining atmosphere blown away by a solar flare. :shock: And there is an immense amount of heat trapped in the planet. I would guess it still holds much of the heat of its formation from billions of years ago. Periodically, this heat has resurfaced the entire planet by remelting it. Freezing out the atmosphere would allow this heat to begin an escape. What else might it do? If the weight of atmosphere is compressing the surface, what processes might be unleashed? We might freeze it out, explore the surface, then decide to take the sunshade down again ..... 

2) The idea of giving Venus a black moon made of elemental carbon is neat. It would contribute to sunshade. But I don't think it would create a magnetic field. Venus lost all its angular momentum in a giant impact late in its formative phase. Earth got overtaken by one of our LaGrange objects, which struck us a glancing blow and birthed Luna (the Moon). This added to our angular momentum because its energy was added to the system. The Moon carried off a lot of surplus silicates from the stratified Earth, thinned our crust and allowed tectonics to persist to the present day, among other things. Venus has a thick crust to trap its heat. Its Lagrange object smashed into it head-on, robbing it of angular momentum (it actually rotates in reverse) and leaving it tidally locked to the Sun. This is the situation which the recently discovered exoplanet Gliese 581c would be in. The tidal friction between Earth and Luna as mediated through our liquid oceans has been dissipating our angular momentum ever since, so that Luna retreats about 10cm every year. Right after Theia's impact, Earth's rotation period was about 5-6 hours, for a year of about 1500 days (same number of hours, you understand, but more days because fewer hours per day). In the preCambrian, our year had about 450 days and perhaps 21-22hrs per day. So if we lift matter off Venus and put it into orbit, the lack of angular momentum should mean this moon could escape Venus orbit very easily, or decay and crash into the surface. It needs torque to keep it all in place, like a gyroscope. I cannot see how we can impart energy into the system without using an impact by an NVA and then the results are potentially chaotic.

3) I think sulphur in the atmosphere is a bigger problem chemically than any other problem addressed so far -- bigger than CO2, for instance. Look up sulphuric acid or vitriol on wikipedia. There is even a section on its role in Venus and how the Sun breaks down CO2 into CO and O2 and then combines that with S to make H2SO4. It ties up all the free hydrogen and oxygen. It destroys water vapour. Plus sulpuric acid will eat any flying vessel we put on the planet. If we can scrub the sulphur out of the atmosphere, then good. But if the planet itself is producing more of it from below, volcanically, then we shall never come to the end of it. Tin appears to be the best metal to combine with it -- you get SnSO4 plus two H2O molecules plus SO2 (sulphur dioxide). Does anyone know of a purely catalytic reaction which will process the sulphur without destroying the raw materials?

4) I think flying cities are out of the question, unless weight proves to be an advantage in staving off hurricane force convection winds or some such thing. Best to disperse resources. I see flying ovoid bubbles with the nature of farms, 3-5 families per bubble, maybe 1km2 each. Solar power, yes, but perhaps with a wind turbine as well, mounted on top like a beanie cap...  8) ... just in case the bubble gets stranded in the doldrums on the dark side of the planet.  :shock: The skin of the bubble will be multilayered with water in the layers and the water will be stocked with algae. Venusian atmosphere can be pumped through the water, making a carbonated pond for the algae. The skin of water and algae will filter out a lot of the UV rays and make life inside the bubble friendlier to higher lifeforms -- food crops and small animals. Bubbles may sport lattices of catalytic metals for scrubbing the atmosphere as they go along. This cannot be done too quickly because, even though it is catalytic, the catalyst will get its reactive surfaces clogged up by the byproducts of the reaction. They will need scrubbing. But this can be a cottage industry, along with weaving fullerenes.

5) People have talked about seeding the atmosphere with algae and letting them do the work, but this fails without water or if they sink into the furnace. People have also talked about flying cities in the clouds. How about combining these ideas? Before the flying cities, there must be flying farms. Before the flying farms, let there be flying algae. I think the first step in colonising Venus is to make fullerene capsules, buoyed by Earth air and populated by algae and water. Figure out some way to keep the algae in a friendly environment while bringing Venus CO2 in for them and siphoning off the water and oxygen they produce. It might not even have to be manned.

Bryan