MagnaCool--Habitable Exoplanet!

[Geronimo]

Originally posted by Berzerker


We also have evidence of a bombardment around or shortly after 4 bya, so "usual" would mean planets that haven't been plastered by asteroids a 1/2 billion years after they formed. And you asked for old news



See

I think you're completely misunderstanding my question and/or I'm misunderstanding your reply.

I'm wondering how we guess what in our solar system is atypical with respect to the general population of stellar systems.

For instance yes, there was heavy bombardment in our system. Don't our models predict such bombardments? Do we have no models that predict a venus or a uranus? Do we guess that our models are accurate and our system has more oddballs than usual or do we guess that the models are fundamentally lacking and we wouldn't know a planetary oddball if it bit us in the arse?

[Berzerker]

For instance yes, there was heavy bombardment in our system. Don't our models predict such bombardments?

Models are based on the heavy bombardment being fact, we know it happened so theories of planetary formation are influenced by that knowledge. The Oort Cloud is a theory based on the existence of comets. But this really doesn't tell us how planets form. Maybe they form thru accretion and the bombardment occurs everywhere until smaller stuff is swept up by the planets. But we got an asteroid belt too, so debris hasn't been swept up even after nearly 5 billion years. If something happened to create all that debris after the planets had formed then we're off on the models wrt timing if not more.

Do we have no models that predict a venus or a uranus?

Sure, massive collisions. But do we define that as "usual"?

Do we guess that our models are accurate and our system has more oddballs than usual or do we guess that the models are fundamentally lacking and we wouldn't know a planetary oddball if it bit us in the arse?

I dont think we can use our system as "usual", there was a collision that sent debris flying around ~ 4 bya. After 4 1/2 billion years I'd expect a stable solar system with planets all spinning in the same direction and in similar fashion. Chaos was introduced into our system after the planets followed the "usual" processes.

[Impaler[WrG]]

Don't models show huge amounts of atmosphere being blasted off of planets so close to their primary early in the stellar evolution unless the planet is substantially larger than this one?

Stars are usually dimmer in their early days and gradually heat up as they age. I'm not sure of this stars age but its likly older then earth as these stars can burn for several times greater then the current age of the universe. The planetary accretion models I've heard of involve the planets being mostly formed before the stars fusion really ignites and the light pressure then blows away (or paradoxically sucks in) the remaining dust and gas.

Large planetary bodies can lose gases from their upper atmospheres over time but this will depend on a balancing of surface gravity and starlight intensity. The effect is like a membrane only gases below a particular molecular weight will escape in significant quantity. The Earth will lose Hydrogen and Helium gas in this way but all Hydrogen is locked in water which is too heavy to escape, Water can be broken down by UV light but the Ozone layer protects it.

Venus probably lacked an Ozone layer (free Oxygen is required for an Ozone layer and life is believed to be required for free Oxygen to be present as no natural process creates it) and saw all of its water broken down and they Hydrogen stripped from the planet. The remaining Oxygen combined with Carbon and oxidized the crust to create the Hellish atmosphere we now see.

Though the atmosphere is 100 times denser then Earths the two planets probably started off with nearly identical compositions and complements of gases. If all the Carbon dissolved in the earths Ocean and locked in geologic deposits (fossil fuels) were liberated and combined with all the Oxygen in the Ocean it would almost perfectly match the conditions on Venus, in fact this will probably happen several billion years in the future as the sun heats up and boils away the oceans, then the hydrogen and vulcanism / erosion exposes the previously trapped carbon in the crust.

So taking all that into account we can see that the planets fate will depend greatly on its composition. If its Icy and thus less dense the surface gravity would drop perhaps preventing a too thick mantle of gases accreting and a Titan like Tundra might result. If the composition is Earth like then it seems likely that the atmosphere will be thicker probably containing Helium but not Hydrogen. A thick atmosphere distributes heat very effectively on a tidily locked planet (Venus is almost locked with the equivalent of an 88 day Day yet the night day temperature are virtually identical) so its unlikely to be the half baked / frozen scenario typical in the Sci-Fi treatment of RedDwarf bound planets. I think the thick atmospheres green-house effect would boil its oceans but unlike Venus the Hydrogen might not strip off because Red Dwarf stars produce very little UV radiation so it might be left with a Supper muggy atmosphere containing Oceans worth of water and plenty of CO2 as well. The Surface would be Venus hot if not more so, theoretically floating organisms might live in the cloud levels as has been imagined in the atmosphere of Jupiter.

[Dauphin]

Originally posted by Berzerker
I think he's talking about a ship moving toward or away from the galactic center

Me too. Though the effect of a 20ly movment is negligible.

A far more important consideration is being able to plot a correct course, Pioneer has already shown odd behaviour and the rotation speeds of stars around the galactic centre are notoriously funky.

[Berzerker]

Venus probably lacked an Ozone layer (free Oxygen is required for an Ozone layer and life is believed to be required for free Oxygen to be present as no natural process creates it

I thought lightning produces ozone, there is a rather unique odor when lightning is really active.

[Geronimo]

Originally posted by Impaler[WrG]


Stars are usually dimmer in their early days and gradually heat up as they age. I'm not sure of this stars age but its likly older then earth as these stars can burn for several times greater then the current age of the universe. The planetary accretion models I've heard of involve the planets being mostly formed before the stars fusion really ignites and the light pressure then blows away (or paradoxically sucks in) the remaining dust and gas.

Large planetary bodies can lose gases from their upper atmospheres over time but this will depend on a balancing of surface gravity and starlight intensity. The effect is like a membrane only gases below a particular molecular weight will escape in significant quantity. The Earth will lose Hydrogen and Helium gas in this way but all Hydrogen is locked in water which is too heavy to escape, Water can be broken down by UV light but the Ozone layer protects it.

Venus probably lacked an Ozone layer (free Oxygen is required for an Ozone layer and life is believed to be required for free Oxygen to be present as no natural process creates it) and saw all of its water broken down and they Hydrogen stripped from the planet. The remaining Oxygen combined with Carbon and oxidized the crust to create the Hellish atmosphere we now see.

Though the atmosphere is 100 times denser then Earths the two planets probably started off with nearly identical compositions and complements of gases. If all the Carbon dissolved in the earths Ocean and locked in geologic deposits (fossil fuels) were liberated and combined with all the Oxygen in the Ocean it would almost perfectly match the conditions on Venus, in fact this will probably happen several billion years in the future as the sun heats up and boils away the oceans, then the hydrogen and vulcanism / erosion exposes the previously trapped carbon in the crust.

So taking all that into account we can see that the planets fate will depend greatly on its composition. If its Icy and thus less dense the surface gravity would drop perhaps preventing a too thick mantle of gases accreting and a Titan like Tundra might result. If the composition is Earth like then it seems likely that the atmosphere will be thicker probably containing Helium but not Hydrogen. A thick atmosphere distributes heat very effectively on a tidily locked planet (Venus is almost locked with the equivalent of an 88 day Day yet the night day temperature are virtually identical) so its unlikely to be the half baked / frozen scenario typical in the Sci-Fi treatment of RedDwarf bound planets. I think the thick atmospheres green-house effect would boil its oceans but unlike Venus the Hydrogen might not strip off because Red Dwarf stars produce very little UV radiation so it might be left with a Supper muggy atmosphere containing Oceans worth of water and plenty of CO2 as well. The Surface would be Venus hot if not more so, theoretically floating organisms might live in the cloud levels as has been imagined in the atmosphere of Jupiter.

agreed. I don't see how venus-like conditions would be considered an unexpected result.

[Ned]

Originally posted by Dauphin


Me too. Though the effect of a 20ly movment is negligible.

A far more important consideration is being able to plot a correct course, Pioneer has already shown odd behaviour and the rotation speeds of stars around the galactic centre are notoriously funky.

So your saying we would not have to track a spiral course, but could go almost straight towards the objective almost ignoring our relative rotational velocities?

You also suggest that essentially the same energy is required regardless of direction we take, towards or away from the galactic center.

IIRC, it takes US 250 million years to orbit the galaxy. I assume we can reach the other planet in a small fraction of this time, which does suggest that we can go almost straight there from here.

But seriously, how long would it take going 100k miles per hour?

[Ned]

I just did a rough calcultion of my own and came up with approximate 6,666 years to go one light year at that speed. That means it would take around 140k years to reach the new planet.

About right?

[Ned]

If these figures are even remotely correct, we are going to have to invent something that can go dormant for a very long time and still work satisfactorily upon arrival more than 100,000 years from now.

Impossible is what I am thinking.

[Odin]

Originally posted by Berzerker
A small nebula collapses and barely has enough material for a small star to ignite?

Actually, most stars (including the Sun, most likely) start out in star clusters derived from one huge nebula (like the Great Nebula in Orion), and that cluster has starts of a variety of masses, the stars of higher mass being far more rare then stars of lower mass, 80% of all "main sequence" (hydrogen-fusing) stars are red dwarfs. over a few hundred million years the cluster disperses and the stars go their separate ways.

[Odin]

Originally posted by Berzerker


I thought lightning produces ozone, there is a rather unique odor when lightning is really active.

Stratospheric ozone is produced by the interaction with atmospheric oxygen and UV light. can't have ozone unless you have the oxygen to make it from.

[Krill]

wrong...

[Odin]

Originally posted by Krill
wrong...

[KrazyHorse]

Originally posted by Ned
But seriously, how long would it take going 100k miles per hour?

3*10^8 m/s * 3600 s/hr ~ 10^12 m/hr

100000 mi/hr * 1600 m/mi = 1.6*10^8 m/hr = 1.6*10^-4 c

20/1.6*10^-4 = 120000 yr

[Geronimo]

Originally posted by KrazyHorse


3*10^8 m/s * 3600 s/hr ~ 10^12 m/hr

100000 mi/hr * 1600 m/mi = 1.6*10^8 m/hr = 1.6*10^-4 c

20/1.6*10^-4 = 120000 yr

What would be the best way to estimate the fastest speed that could be obtained in which the mass of shielding against impacts using currently available materials would be less than say a quarter of the vehicle mass?

I'm wondering what the upper speed limit is without resorting to speculative exotic shielding strategies.