Inhabitable Planets Too Close Together?

JohnRoth wrote:The biggest issue that none of these proposals deal with is that, in a pre-oxygen environment, there are a huge number of oxygen sinks, such as reduced iron, which will promptly absorb all the oxygen you can produce.

If we're processing ocean water or pulverizing surface oxides aren't the "O2 Sinks" already full? As long as we deal with the recombination problem -- eg keep separate elements separate and dispose of the waste portion -- aren't we simply drawing from stored Oxygen?

The problem with real-world oxygenation as an example is that process started from a theoretical single first mutated algae cell. Terraforming won't start with one algae cell or one grass seed or one genie-coral polyp, it will start from a point a couple of billion years of cell division advanced from that theoretical first single mutation.

Terraforming through the biosphere won't happen in 30 years, but I would not seriously expect it to take 2.6 billion years either.

A question for SWM and namelessfly: Is sulfur going to be a problem in a pre-biotic atmosphere? AFAIK, all the sulfur compounds are at least somewhat toxic. Will they settle out on their own? Or is some mechanism going to be needed to eliminate them?

Weird Harold wrote:

JohnRoth wrote:The biggest issue that none of these proposals deal with is that, in a pre-oxygen environment, there are a huge number of oxygen sinks, such as reduced iron, which will promptly absorb all the oxygen you can produce.

If we're processing ocean water or pulverizing surface oxides aren't the "O2 Sinks" already full? As long as we deal with the recombination problem -- eg keep separate elements separate and dispose of the waste portion -- aren't we simply drawing from stored Oxygen?

That's two different questions. First, Earth had lots of water before oxygenation started, and the oxygen sinks (that is, reduced iron and lots of etceteras), weren't full. In fact, a lot of "how life started" scenarios assume large quantities of dissolved iron in the ocean. In other words, the existing oxygen is pretty much locked up in the water to start with.

The second question assumes starting with lots of oxides. That's a fundamentally different set of assumptions. I don't know how you'd get a planet like that to start with, which doesn't mean that it might not exist.

Weird Harold wrote:The problem with real-world oxygenation as an example is that process started from a theoretical single first mutated algae cell. Terraforming won't start with one algae cell or one grass seed or one genie-coral polyp, it will start from a point a couple of billion years of cell division advanced from that theoretical first single mutation.

We don't know when the first cells arose that started releasing oxygen. What we (that is, geologists) know is when there started to be enough oxygen for detectable amounts of oxides to be deposited. That takes a lot more than a single cell.

Weird Harold wrote:Terraforming through the biosphere won't happen in 30 years, but I would not seriously expect it to take 2.6 billion years either.

That's arm waving. Our single example provides no support for it being able to take substantially less.

JohnRoth wrote:

biochem wrote:Most of these ideas aren't mutually exclusive. The colonists could use industrial production methods AND drop comets AND use genie coral etc (although while they're at it they might as well toss in some other genie organisms, archaebacteria can survive in some extremely harsh environments and could be engineered to do a variety of useful things). Although as an order of addition problem, if I was going to combine techniques I'd drop comets first as dinosaur killers may disrupt the new ecosystem and may damage any industrial structures.

The problem that namelessfly is trying to deal with is that the only example we have of a purely biological process going from a pre-oxygen atmosphere to one with a modern proportion of oxygen took about 2.5 billion years to get there. This is probably somewhat outside of the payback horizon for even the most far-sighted transstellar to consider.

That doesn't mean it couldn't be done faster, but a single example doesn't provide any support for the notion.

The biggest issue that none of these proposals deal with is that, in a pre-oxygen environment, there are a huge number of oxygen sinks, such as reduced iron, which will promptly absorb all the oxygen you can produce. That's what took close to a billion years of that 2.5 billion before there was any more than trace amounts of oxygen in the atmosphere.

namelessfly wrote:This was in the back of my mind.

The total capacity of the Oxygen sinks is important but the rate at which the Oxygen sinks can absorb Oxygen is critical. If your process for creating Oxygen can exceed Oxygen sequestration by a wide enough margin, you can create and maintain breathable atmosphere.

Probably true. However, that would leave you with a planet that had an oxygen atmosphere, but with an ocean that was substantially different than it is today, and probably highly inimical to life as we know it, which is adapted to environments which don't have those oxygen sinks.

In other words, filling the oxygen sinks is probably not optional before the planet becomes habitable.

I am presuming that the terraforming operation would include routine uses of nuclear explosives to create and maintain high altitude dust clouds that would absorb sunlight reflected and focused by orbiting mirrors.

JohnRoth wrote:

namelessfly wrote:Here is a good reference on Jean's escape mechanism.

Forgot the link, damn it.

http://sci.esa.int/science-e/www/object ... ctid=50647

The bottom line is that at 1,000 K which is the temp at the top of the thermosphere, rms for Oxygen molecules is 1 km/s while rms for hydrogen molecules is 4 km/s. While the rms of Hydrogen is far short of escape velocity, a significant fraction of molecules (1 in 10,000) exceed escape velocity. CO2 has a higher molocular mass than Oxygen but rms velocity is only marginally lower.

This suggests that heating theatmosphere (or a significant portion of it) to about 16,000 K would result in Oxygen having the same velocity profile as hydrogen at 1,000 K. However; at this temperature you will have mostly atomic oxygen so 10,000 K would be quite adequate.

An orbiting solar mirror of perhaps 1,000 km diameter that focuses sunlight onto a region of atmosphere a few kilometers in diameter would create a region of rapid cook off.

What proportion of the energy gets absorbed by the atmosphere in that focus sphere, and what proportion goes through? To reiterate an earlier point, I have a suspicion that what you'd be doing is melting the surface.

namelessfly wrote:I am presuming that the terraforming operation would include routine uses of nuclear explosives to create and maintain high altitude dust clouds that would absorb sunlight reflected and focused by orbiting mirrors.

Maybe, but the Honorverse does feature chemical explosives that can match or exceed r/w nuclear explosives. But they also feature "industrial nukes" (as used in Green Pines.)

It would depend on how much residual radiation is acceptable.

The difficulty of eliminating reducing agents such as free Iron in the biosphere that would react with free Oxygen is perhaps overestimated. The reaction rate between Iron and Oxygen at room temperature is rather low and only free iron close to the surface would be able to react with atmospheric Oxygen. The only problematic Oxygen sink would be dissolved free Iron in planetary Oceans.

Based on this reference here:

http://www.jstor.org/discover/10.2307/4 ... 4098169283

The solubility of free iron in water is quite low. This is especially true if dissolved CO2 in the oceans is mi imized by stripping off a CO2 atmosphere prior to establishing an Oxygen atmosphere. Once the initial inventory of dissolved Iron is Oxidized, the limiting factor would be the rate at which new Iron is eroded and dissolved. Well tended biological processes would
probably do the job of maintaining the Oxygen supply but augmenting with continued industrial
processes might be needed.

namelessfly wrote:...if dissolved CO2 in the oceans is mi imized by stripping off a CO2 atmosphere prior to establishing an Oxygen atmosphere. ...

Would it really be wise to discard the CO2? It occurs to me that could create a carbon shortage that could limit the expansion of biota. Granted, t can't be left as gaseous CO2, but the biosphere will eventually need a large supply of carbon if it is going to be CHON based biota.

Weird Harold wrote:

namelessfly wrote:...if dissolved CO2 in the oceans is mi imized by stripping off a CO2 atmosphere prior to establishing an Oxygen atmosphere. ...

Would it really be wise to discard the CO2? It occurs to me that could create a carbon shortage that could limit the expansion of biota. Granted, t can't be left as gaseous CO2, but the biosphere will eventually need a large supply of carbon if it is going to be CHON based biota.

Based on allowable limits here:

http://ntrs.nasa.gov/archive/nasa/casi. ... 029352.pdf

Terraformers might leave enough CO2 to form a 1% atmosphere at STP which would provide an adequate CO2 reservoir.

Alternatively; you might draw down CO2 to 10% and allow plants to sequester most of it.

namelessfly wrote:Based on allowable limits here:

http://ntrs.nasa.gov/archive/nasa/casi. ... 029352.pdf

All I'm getting from that link is a blank.

namelessfly wrote:Terraformers might leave enough CO2 to form a 1% atmosphere at STP which would provide an adequate CO2 reservoir.

Alternatively; you might draw down CO2 to 10% and allow plants to sequester most of it.

My concern was that in a pre-biota system, what other carbon is there (in any significant quantity) besides CO2, CO and possibly Methane?

1% CO2/CO might be a good value to have if the are significant carbon reserves already sequestered, but even 10% atmosphere might not be enough if there is no existing carbon sink.