Wet Mercury:

[Prospernia]

I was going to create a black and white map, with arcologies, of an early Mercurian-world, but I colorized it and it hence has no human-settlements on it:

I found an map of Mercury, two-colored it, then, I expanded it and then added water and colorized it: I wanted it to be like early-Earth, but I have to remake the equator if I want to match Earth's early rotation (days that were six-hours long).

If K-Type Star: 0.3 AUs
If G-Type Star: 0.75 AUs
Gravity: 0.5 gees.
Rotation: 32-hours.
Axial-Tilt: Zero-degrees.
Temperature: 100+ degrees Celsius.
Air-Pressure: twenty times that of Earth's; on the surface, every where you look, it looks like you're in a fish-bowl.
Water is still liquid, despite being beyond the boiling point: it's green because it's full of iron.
Atmosphere: 1% oxygen, thanks to solar-wind breaking down CO2.  Still not enough to breathe on your own.
Geology: Mostly volcanoes: the planet has no mantle; just a thin-crust of seven-miles at the most on top of a molten, metallic-core.  The world is mineral and metal-rich.
Life: primitive single-cell extremophiles, living in the ocean near volcanic-vents. Life is a combination of carbon/silicon-based with DNA in spherical-clusters, not strands.



The original-Map is huge! 
https://iili.io/JGh5TGI.gif

[Daryk]

I'm not sure a crust of only 7 miles is habitable over a molten core...

[Ajax_Wolf]

I'd like to know what is in the other 99% of the atmosphere?

And I probably botched the calc, but 1% of O2 at 20 atmos should be enough to keep you alive without burning you up.

[Prospernia]

I'd like to know what is in the other 99% of the atmosphere?

And I probably botched the calc, but 1% of O2 at 20 atmos should be enough to keep you alive without burning you up.

That seems like a ligit number. Might need to filter the O2 through a cooling-system though.

The other 99% is probably mostly C02 and Nitrogen, with sulfur and other volcanic gasses.

I'm not sure a crust of only 7 miles is habitable over a molten core...

I just realized that, with only seven-miles, either they world has active and I mean active plate-tectonics or massive volcanism to reduce the heat.

[rufusexc]

I didn't quite understand, is the planet like Mercury also in size? How does it have an atmospheric pressure 20 times that of the Earth? It should be bigger than Earth. In addition, a temperature of 100 degrees Celsius is too high for humans.

[Prospernia]

I didn't quite understand, is the planet like Mercury also in size? How does it have an atmospheric pressure 20 times that of the Earth? It should be bigger than Earth. In addition, a temperature of 100 degrees Celsius is too high for humans.

A small planet can have more air-pressure than Earth; take Venus for instant; it's a little smaller than Earth, yet has an atmosphere 90 times that of Earth's.

Early Earth, had an atmosphere 27-times present, and an average temperature of 230 °C.  At that time, Earth did have liquid-oceans of water. and perhaps, about 200MYA after formation. However, the oceans absorbed the CO2 over time.

[rufusexc]

But Venus' atmosphere is denser than Earth's, with carbon dioxide accounting for about 95-96% of the atmosphere.
Then consider that carbon dioxide is a heavier gas than air. It tends to accumulate in the lower layers of the atmosphere. This generates a higher atmospheric pressure.
Venus has a radius of 6,051.8 km and Earth has a radius of 6,371 km.
Mercury is much smaller than Earth (almost a third) and is also smaller than Mars.
Considering that Mars has a The atmospheric pressure at ground level ranges from about 7 to 11 millibars, while the average pressure at sea level on Earth is 1000 millibars.
A planet like Mercury can never have a pressure 20 times that of the Earth.

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[Prospernia]

. . .
A planet like Mercury can never have a pressure 20 times that of the Earth.

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Is that because Mercury does not possess the amount of carbon-dioxide to out-gas to create a thicker-atmosphere?

[AlphaMirage]

Is that because Mercury does not possess the amount of carbon-dioxide to out-gas to create a thicker-atmosphere?

It doesn't have the mass but it also gets it stripped away by solar radiation so it won't accumulate, it gets dissipates

[Prospernia]

It doesn't have the mass but it also gets it stripped away by solar radiation so it won't accumulate, it gets dissipates

Not if it as a strong magnetic-field like Mars did in the past.

[Daryk]

The lack of mass is way more important for that...

[Prospernia]

The lack of mass is way more important for that...

Not sure what you mean: Mercury has a magnetic-field still, abet, weak. 

[Daryk]

For holding on to an atmosphere...

[rufusexc]

If there is an atmosphere on Mercury you could measure it in millimeters, maximum in centimeters in height, not like those of Venus and Earth...

[Prospernia]

For holding on to an atmosphere...

Earth, Mars, Mercury and Venus probably all started out with a thick-atmosphere, then lost or increased it over time; Mars retained it's thick-atmosphere up to 3.8BYA and we're not sure about Mercury, but, it has a much larger-core than Mars and may have held it longer. It's slow-rotation may have turned it's magnetic-field off.

[rufusexc]

Actually, from the information so far, Mars has cores with a radius between 1500 and 2100 km.
What makes the geomagnetic field stronger or weaker is the presence of a rotating liquid ferromagnetic core.
Mercury's crust is also small because of the proximity of the Sun, the extreme temperatures the planet is subjected to, with the possibility that part of the crust has even evaporated.

[Daryk]

I don't know that Mercury ever had a thick atmosphere.

[Prospernia]

I don't know that Mercury ever had a thick atmosphere.

It has frozen water in a few craters at its poles; like the Moon, at one point, it had water.

[Daryk]

Well, like the moon, that doesn't necessarily mean it had a thick atmosphere...

[worktroll]

The polar ice is probably collected from comet impacts. The comets vaporise, the gas spreads, some gets into the polar craters and freezes, and remains shadowed. Neither the Moon nor Mercury would have had oceans like primitive Earth had, and lost, and got replenished by more comet impacts.

(I have a piece of the Jack Hills Gneiss - a Hadean age rock showing zircon crystals that form only in the presence of water. Which was most unexpected at the time.)

[Daryk]

That's very cool Worktroll! :)

[rufusexc]

Mercury behaves with the Sun like the Moon with the Earth, that is, it always shows the same side. In the case of Mercury it implies, even in the absence of a real atmosphere, which could disperse heat, that in the part exposed to the Sun temperatures of 400° C and more are reached.
On the opposite side, on the other hand, temperatures inside some craters can reach as low as -200° C, and it is precisely in these craters that ice should be present, not at the poles.

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[Daryk]

The technical term is "tidally locked". :)

[ThePW]

The polar ice is probably collected from comet impacts. The comets vaporise, the gas spreads, some gets into the polar craters and freezes, and remains shadowed. Neither the Moon nor Mercury would have had oceans like primitive Earth had, and lost, and got replenished by more comet impacts.

(I have a piece of the Jack Hills Gneiss - a Hadean age rock showing zircon crystals that form only in the presence of water. Which was most unexpected at the time.)

Given the size of Mercury, has anyone speculated that Mercury either was prevented to gain more mass due to proximity to SOL or was Mercury the modern result of Thea (because its so small, could it be the remains of the collision, maybe even the solid core of some other world in the past?)

[worktroll]

Yes. Its been speculated that Mercury was originally larger, but suffered a major collision, stripping off a lot of the crust and leaving a thinly covered leftover large core. The proximity to the sun probably stopped the debris from condensing into a moon or moons.

Probably well before rhe late bombardment, and possibly around the time Jupiter was doing its crazy fandango thing.

[Prospernia]

It's been theorized that Mercury formed in the location Earth is, but was pushed to it's close orbit to the Sun.

[worktroll]

Okay, I'm old, and the whole "shuffling planets" things spins my brain, but there's too much evidence that something did re-order the planets significantly.  The main problems being the "ice giants", which couldn't have formed in their current positions.

[Daryk]

Planets playing bumper cars shouldn't be too surprising... ;D

[worktroll]

Given the stability of the current system, it is actually quite surprising. They have to make assumptions like "a third ice giant got ejected violently from the system" to provide any mechanism for removing the excess angular momentum.

[Prospernia]

Okay, I'm old, and the whole "shuffling planets" things spins my brain, but there's too much evidence that something did re-order the planets significantly.  The main problems being the "ice giants", which couldn't have formed in their current positions.

Everything was going good in the accretion-disk, until the, "Clumps", got to the size of planetismals, and then, everything went crazy; Jupiter, fell in and robbed Mars of some it's material, only to be stopped by Saturn.  Venus got hit and knocked upside-down; Earth got hit by Thea, and Mercury, almost got sent into the Sun.