Water vapour atmosphere creation on Mars

Terraformer · 2024-07-04 15:50:09

In the Ceres thread, Calliban suggests launching water from Ceres to Mars to hypersaturate the atmosphere with water vapour which will be dissociated to produce oxygen:

Calliban wrote:

The presence of water on Ceres makes this sort of thing much more achievable.
In fact, Ceres may be key to terraforming Mars, as it is 10% water by mass. Suppose we mount mass drivers on the surface of Ceres. We launch packages of water ice in the opposite direction to Ceres orbital travel, so a portion of the orbital speed is cancelled out. They are given just enough velocity to reduce ther perogee such that it crosses Mars orbit. Eventually, these ice packages will collide with Mars exploding in its upper atmosphere. This will supersaturate the upper atmosphere with water vapour. In addition to creating a strong greenhouse effect, solar UV will break the water into hydrogen and oxygen. The former would rapidly escape Mars, with the oxygen being trapped and accumulating within the atmosphere.
We would need to deliver 7.2E17kg of water to the Martian atmosphere to produce a minimal breathable surface oxygen concentration. That is 82 million tonnes per hour, for 1000 years.

This would be a sizeable outgoing. Far easier would be to build mirrors and use Mars' own resources. Though it has far less water than Earth, Mars still possesses enough water to give it a ~70m layer globally (ignoring topography). If we were to use this as the sole source of oxygen, getting to a breathable amount would sacrifice less than 10% of this. To get above the triple point would take far less.

To raise ice from -60c to melting point would take ~130 MJ/tonne. To melt and then vapourise it would take far more, ~2600 MJ/tonne. Call it 3 GJ/tonne to make it easy.

How much mass do we need for 1mb of oxygen partial pressure on Mars? The surface area is ~1.5e14 m^2, and we would need ~25kg per square metre. So ~3.75e15 kg; accounting for the hydrogen we'd be getting rid of, call it 5e12 tonnes of water.

What if we wanted to add 1mb of atmosphere each year? There are ~3e7 seconds in a year, so we would need to be vapourising 5e12/3e7 tonnes per second. Call it 2e5, or 200,000 tonnes a second (ouch). Each tonne would take 3e9 J to liberate, so we would need a total power of... 6e14 W. 600 terawatts. That's a lot of power.

How big a mirror would we need? Insolation at Mars is ~600 W/m^2, so each square kilometre could provide 600 MW. 6e8 W. We would need 1e6, one million, square kilometres of mirror to provide for that level of power from sunlight. Not quite continent sized mirrors. But about five Britains worth. Yikes. But when reengineering planets that's a pretty minor task really.

(EDIT: I messed up a division and end up tripling it)

Last edited by Terraformer (2024-07-04 15:56:41)

tahanson43206 · 2024-07-04 17:12:18

This post is reserved for an index to posts NewMars members may contribute over time.

Best wishes for success with this ambitious new topic.

(th)

Terraformer · 2024-07-04 17:19:45

However. We do not need even 1mb to get substantial benefits from having some oxygen. Significant UV protection comes from ozone at 0.2mb (pretty sure this was in a Martian context). With 10,000 km^2 (1250 5km radius mirrors?), we could get that in two decades, at which point methane will be able to persist for far longer periods and provide global warming. There's still a lot of benefits to be had from even very trace atmospheres.

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#1 2024-07-04 15:50:09

Water vapour atmosphere creation on Mars

#2 2024-07-04 17:12:18

Re: Water vapour atmosphere creation on Mars

#3 2024-07-04 17:19:45

Re: Water vapour atmosphere creation on Mars

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