Inhabitable Planets Too Close Together?

namelessfly wrote:But you don't need anywhere near that much hydrogen for fusion fuel. That much hydrogen would be enough to run the entire planet for a millennium!

Weird Harold wrote:

namelessfly wrote:But you don't need anywhere near that much hydrogen for fusion fuel. That much hydrogen would be enough to run the entire planet for a millennium!

Then lift it space for use as starship fuel or just vent the excess to space. Hydrogen is fairly easy to come by but the process isn't about producing H2, it's about producing free O2 Collecting gaseous H2 from electrolysis is fairly easy -- presumable any more efficient separation of water process would leave hydrogen equally easy to collect.

Collecting and re-directing free carbon from your pyrolysis process doesn't seem to be possible, let alone efficient.

SWM wrote:

namelessfly wrote:I agree that simply using thermalisis to separate CO2 in an atmosphere in situ is not going to work unless you have something else to bond with the free Oxygen and Carbon. Perhaps hydrogen extracted from Methane from comet could be injected to bond with the free Oxygen to form water that would precipitate out might be a solution. However; it is more plausible to just boil off a CO2 atmosphere from a planet then replace the atmosphere with the proper mix of Nitrogen and Oxygen as well as water if needed for a hydrosphere. Yes, the volumes seem daunting but given the energy budget that an interstellar colony ship should have it should not be that big of a problem. Pick a comet, grab it and bag it, then apply controlled heat to distillation separate the gases that you want, then use your colony ship's fusion rocket as a tug to boost it to the proper orbit. Alternatively; you might thermolisis to extract Oxygen from an orbiting moon to drop on planet.

We can scream about how huge the volumes and masses are but if humans have the technology to build a fusion rocket powered colony ship then this terraforming is within their energy budget. Perhaps no one has realized this because I am the first to crunch the numbers?

Think about it from a philosophical perspective. We worry about our current industrial civilization's 1eex13 Watt energy budget screwing up Earth's environment but our interstellar colony ship will have an energy budget of 1eex15 to 1eex18 Watts. Finding the energy to process and move the relevant masses would probably be less problematic than properely understanding the Macro chemistry to create a viable ecosystem.

Why do you keep harping on the energy budget? No one has suggested that energy budget is a problem!

How long do you think it would take to "boil off" the existing atmosphere? This is called Jeans Escape. Unless you raise the temperature high enough, it will take millennia. At the temperatures we will be dealing with, all the gasses will be dissociated and probably ionized. If the mean velocity of atomic oxygen is equal to escape velocity, the temperature would be around 64,000 degrees Celsius. Let's say we raise the temperature of the atmosphere to 100,000 C to get rid of it. (Note--at this temperature, a lot of heavier elements on the surface will be volatizing into the atmosphere. But presumably they will condense again once it cools off.)

The heat capacity of the atmosphere is on the order of 1 J/(g K). For simplicity, let's assume that stays true at all temperatures and pressures, even though we know it is more than an order of magnitude more at higher temperatures. The mass of Earth's atmosphere is 5e18 kilograms. So to raise the temperature of the atmosphere to 100,000 C, we need to apply 5e26 Joules. You suggest that a slowship can generate 1e18 Watts. If you had 1,000,000 slowships, it would take 100 years to raise the temperature of the atmosphere to that temperature.

Of course, it would actually take much longer, because the planet would be radiating heat at a tremendous rate. In fact, that is 20 times the surface temperature of the sun. At 100,000 C, the planet will be radiating 3e27 Watts! Even if we go with 64,000 C, it will be radiating 5e26 Watts. In 1 second, the atmosphere would radiate away its entire latent heat, unless it were refreshed constantly!

Conclusion--you can't boil the atmosphere away in less than geological time. At the temperatures that will be practical (far less than stellar temperature), Jeans Escape will give an atmospheric half-life of millennia.

SWM wrote:Now let's discuss getting oxygen from comets.

Taking Halley's comet as typical, we can expect over 35% by mass will be oxygen. The density of a comet is around 0.6 g/cc. We will assume, for argument's sake, that sufficient nitrogen or other innocuous gasses will be available from some source; the ratio of nitrogen to oxygen in a comet is far lower than the ratio in the Earth's atmosphere.

Namelessfly suggested using comets around 15 km in diameter. Such a comet would have a mass of 1e12 kg, of which 3.7e11 kg will be oxygen. To get sufficient oxygen for the new atmosphere, you will need more than 3,000,000 comets! [edit]Sorry, miscalculated. The comet would be 1e15 kg, and you would need 3000 comets[/edit] And, of course, you will actually have to process all those comets, because the oxygen will be in the form of H2O and CO.

namelessfly wrote:Someone wrote:
. The heat capacity of the atmosphere is on the order of 1 J/(g K). For simplicity, let's assume that stays true at all temperatures and pressures, even though we know it is more than an order of magnitude more at higher temperatures. The mass of Earth's atmosphere is 5e18 kilograms. So to raise the temperature of the atmosphere to 100,000 C, we need to apply 5e26 Joules. You suggest that a slowship can generate 1e18 Watts. If you had 1,000,000 slowships, it would take 100 years to raise the temperature of the atmosphere to that temperature.

Momentarily stipulating the 5eex26 Joule energy requirement, a slow ship engine or alternatively a solar collector that generates 1eex18 Watts will generate 3eex25 Joules in one year or 3eex26 Joules in a decade or 6eex26 Watts in two decades.

Take two six packs and call me in the morning.

namelessfly wrote:

SWM wrote:Now let's discuss getting oxygen from comets.

Taking Halley's comet as typical, we can expect over 35% by mass will be oxygen. The density of a comet is around 0.6 g/cc. We will assume, for argument's sake, that sufficient nitrogen or other innocuous gasses will be available from some source; the ratio of nitrogen to oxygen in a comet is far lower than the ratio in the Earth's atmosphere.

Namelessfly suggested using comets around 15 km in diameter. Such a comet would have a mass of 1e12 kg, of which 3.7e11 kg will be oxygen. To get sufficient oxygen for the new atmosphere, you will need more than 3,000,000 comets! [edit]Sorry, miscalculated. The comet would be 1e15 kg, and you would need 3000 comets[/edit] And, of course, you will actually have to process all those comets, because the oxygen will be in the form of H2O and CO.

Oh, Bother.

Diameter of a planet is on the order of 10,000 Km, right?

This is 1eex7 meters, correct?

Surface area is then on the order of 3eex14 square meters.

At ten tons of atmosphere per square meter that is 1eex4Kg/m^2 x 3eex14 square meters = 3eex18 Kg of atmosphere.

Now assume our comet is on the order of ten km in diameter.

That is 10,000 or 1eex4 meters, right?

Volume is then on the order of 1eex12 cubic meters.

I got lazy by using an assumed cometary density of 1 rather than .6 but that is 600kg per cubic meter so our comet yields 6eex14 Kg.

OMG, I did make a math boo boo.

We need about 500 comets to make an atmosphere!

I will drink two six packs and call YOU in the morning.

We will actually need more because a lot of that comet is methane which will become CO2.

The E wrote:Wolfram Alpha cites a mass of 5.1441 x 10^18 kilogram for Earth's atmosphere.

SWM wrote:

namelessfly wrote:Someone wrote:
. The heat capacity of the atmosphere is on the order of 1 J/(g K). For simplicity, let's assume that stays true at all temperatures and pressures, even though we know it is more than an order of magnitude more at higher temperatures. The mass of Earth's atmosphere is 5e18 kilograms. So to raise the temperature of the atmosphere to 100,000 C, we need to apply 5e26 Joules. You suggest that a slowship can generate 1e18 Watts. If you had 1,000,000 slowships, it would take 100 years to raise the temperature of the atmosphere to that temperature.

Momentarily stipulating the 5eex26 Joule energy requirement, a slow ship engine or alternatively a solar collector that generates 1eex18 Watts will generate 3eex25 Joules in one year or 3eex26 Joules in a decade or 6eex26 Watts in two decades.

Take two six packs and call me in the morning.

You're right. I goofed badly on the math there. I will grant that it would be possible to strip an atmosphere within a couple decades.