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This is a fascinating analysis, but it doesn't mention the magnetosphere. I'm an amateur, but my understanding is that tidal locking means effectively no rotati

by ak217 3y ago

This is a fascinating analysis, but it doesn't mention the magnetosphere. I'm an amateur, but my understanding is that tidal locking means effectively no rotation with respect to the aspect of the solar wind. No rotation means no coriolis. No coriolis means no dynamo. No dynamo means no magnetic field to protect the planet. No magnetic field means the solar wind will strip the atmosphere, no?

hlava 3y ago
Well, Venus doesn't generate its magnetic field via geodynamo. Instead, it has some sort of weak magnetosphere induced by the interaction of the solar wind with the planet's ionosphere. Also even without this magnetic field, I guess the volatile processes on the surface are enough to keep the atmosphere going.
dakr 3y ago
I was also wondering about the stellar wind stripping away the atmosphere. Planets close enough to their stars to be tidally locked will experience more stellar wind than those farther away and dwarf stars have more flare events than stars like our sun does, exacerbating the problem (plus flares can release a lot of high energy photons, which can break apart structures like DNA).
sfink 3y ago
Yeah, that seems to be the elephant in the room. It's great that planets tidally locked to a red dwarf can block the heat with clouds, and mix the heat around with their atmosphere and ocean. But if being stuck up against a star means their atmosphere will be stripped off, then there will be neither clouds nor wind to do any good. Then again: Mercury has a dynamo-generated magnetic field, yet has the thinnest atmosphere of all of our planets[1]. Venus does not have a dynamo-generated magnetic field[2], yet has an extremely thick atmosphere. So it's not totally cut and dried. And there's of course the possibility of life in subsurface water. If the atmosphere were stripped, must the planet end up dry? Subsurface oceans can still mix the heat around. It could be underneath crust or ice (though the low atmospheric pressure would probably eliminate any ice near the top, so if it's ice it's probably underneath a crusty layer). Could tidal forces themselves drag enough magma around to generate a magnetic field good enough for shielding? The Earth's magnetic field from ocean tides is 20000 times weaker than the main one[3], but that's based on ions dissolved in water pulled by a relatively weak tidal force. What's a few orders of magnitude between friends? 1. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/planetary-magnetic-field https://www.sciencedirect.com/topics/earth-and-planetary-sci... 2. Venus has a small induced magnetosphere from solar wind hitting the ionosphere, but that's probably something that would lead to more loss, not less? 3. https://www.sciencealert.com/esa-swarm-satellite-map-ocean-tides-magnetic-field https://www.sciencealert.com/esa-swarm-satellite-map-ocean-t...
jjk166 3y ago
For Earth-sized planets solar winds don't have much affect. Geologic activity continuously pumps gas into the atmosphere and the planet has sufficient gravity to retain its atmosphere over long time periods. With a thick atmosphere, the losses from solar wind just don't make a dent, it's only for planets with an already thin atmosphere that it becomes a significant factor, and even then it's still not the main contributor. For example solar wind only accounts for about 5% of Mars' current atmospheric loss rate. The component of Mars' atmospheric loss due to the solar wind is about 100 grams per second, which over 10 billion years would remove less than 1% of Earth's atmosphere. Venus, despite having essentially no magnetic field and being even closer to the sun nevertheless has an incredibly thick atmosphere more than 90 times thicker than Earth's.
- XorNot 3y ago
  One of my bugbears about discussions of terraforming Mars really: any atmosphere we added to the planet to give it substantial surface pressure would take hundreds of thousands of years minimum to be lost in any quantity (i.e. by redirecting water ice comets to bombard it with Earth's ocean levels of new gases). Atmospheric loss just isn't a problem compared to the technical challenge of doing the comet redirect (which is actually the most plausible part of the enterprise, compared to the monster which would be developing an ecosystem on a barren planet that stabilizes at a human-habitable point of usefulness and isn't just "walls of sulfur algae" for a few thousand years.

by ak217 3y ago

hlava 3y ago

Well, Venus doesn't generate its magnetic field via geodynamo. Instead, it has some sort of weak magnetosphere induced by the interaction of the solar wind with the planet's ionosphere. Also even without this magnetic field, I guess the volatile processes on the surface are enough to keep the atmosphere going.

dakr 3y ago

I was also wondering about the stellar wind stripping away the atmosphere. Planets close enough to their stars to be tidally locked will experience more stellar wind than those farther away and dwarf stars have more flare events than stars like our sun does, exacerbating the problem (plus flares can release a lot of high energy photons, which can break apart structures like DNA).

sfink 3y ago

Yeah, that seems to be the elephant in the room. It's great that planets tidally locked to a red dwarf can block the heat with clouds, and mix the heat around with their atmosphere and ocean. But if being stuck up against a star means their atmosphere will be stripped off, then there will be neither clouds nor wind to do any good. Then again: Mercury has a dynamo-generated magnetic field, yet has the thinnest atmosphere of all of our planets[1]. Venus does not have a dynamo-generated magnetic field[2], yet has an extremely thick atmosphere. So it's not totally cut and dried. And there's of course the possibility of life in subsurface water. If the atmosphere were stripped, must the planet end up dry? Subsurface oceans can still mix the heat around. It could be underneath crust or ice (though the low atmospheric pressure would probably eliminate any ice near the top, so if it's ice it's probably underneath a crusty layer). Could tidal forces themselves drag enough magma around to generate a magnetic field good enough for shielding? The Earth's magnetic field from ocean tides is 20000 times weaker than the main one[3], but that's based on ions dissolved in water pulled by a relatively weak tidal force. What's a few orders of magnitude between friends? 1. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/planetary-magnetic-field https://www.sciencedirect.com/topics/earth-and-planetary-sci... 2. Venus has a small induced magnetosphere from solar wind hitting the ionosphere, but that's probably something that would lead to more loss, not less? 3. https://www.sciencealert.com/esa-swarm-satellite-map-ocean-tides-magnetic-field https://www.sciencealert.com/esa-swarm-satellite-map-ocean-t...

jjk166 3y ago

For Earth-sized planets solar winds don't have much affect. Geologic activity continuously pumps gas into the atmosphere and the planet has sufficient gravity to retain its atmosphere over long time periods. With a thick atmosphere, the losses from solar wind just don't make a dent, it's only for planets with an already thin atmosphere that it becomes a significant factor, and even then it's still not the main contributor. For example solar wind only accounts for about 5% of Mars' current atmospheric loss rate. The component of Mars' atmospheric loss due to the solar wind is about 100 grams per second, which over 10 billion years would remove less than 1% of Earth's atmosphere. Venus, despite having essentially no magnetic field and being even closer to the sun nevertheless has an incredibly thick atmosphere more than 90 times thicker than Earth's.

XorNot 3y ago
One of my bugbears about discussions of terraforming Mars really: any atmosphere we added to the planet to give it substantial surface pressure would take hundreds of thousands of years minimum to be lost in any quantity (i.e. by redirecting water ice comets to bombard it with Earth's ocean levels of new gases). Atmospheric loss just isn't a problem compared to the technical challenge of doing the comet redirect (which is actually the most plausible part of the enterprise, compared to the monster which would be developing an ecosystem on a barren planet that stabilizes at a human-habitable point of usefulness and isn't just "walls of sulfur algae" for a few thousand years.