Conditions necessary for small, semi-molten planet

[Apollo7]

I am designing a new system about a G4 V type sun, and I would like one, tidally locked terrestrial-type world to be at a distance where:

A) one side faces the parent star at all times
B) the surface is semi-molten

The latter (B) reffers to a condition at which some of the planets surface would be reduced to liquid slag, and others would remain as solids. I know on the Surface of Venus that it is hot enough to melt lead or tin, but its obvious from Magellan imagery that the surface is not flowing per lava. In my case I'd like a planet that could involve both molten (flowing), semi-molten, and solid surface features.

As usual, this is a young system, I am placing it at about 1.24 billion years of age. Is such a planet even possible, I'm wondering if the nightside would remain forozen solid, or would the shifting and movement of the partially liquified sun-lit side cause friction and vulcanism on the night-side?

Any input?

[marc]

How about using the parameters for Jupiter/Io and scaling them up to suit your star?

[Apollo7]

I did consider Io as a model, the current parameters of the planet in question are as follows:

Name: 2324-B
SemiMajorAxis 0.093729 AU or 14,024,352 Km (roughly)
Mass 2.419*10^23 Kg, about 4% that of earth.
Radius 2192.12 Km, about 34% that of earth.
Accel due to Gravity: 3.36 m/s
EscapeVel: 3.8 Km/s
Period 10.33 Days
Rotation: 247.33 Hours
Albedo 0.09
Temp: Day side - 536.2 C, 821 K
Atmosphere: Trace

Star Data - Name: RB872324
Type: G4 V
Surace Temp: 5740 K
Radius 574142 Km

So those are the particulars, as they are now. I am preasently considering altering the orbital parameters, but I am not sure as to what degree I might do so. I did a quick math-exercise on scaling for the Jupiter-Io system and translating it to my star. The data shows I would need to have a planetary distance that is 8 times farther from the star as Io is from Jupiter: meaning - 8 * 442000 = 3389021 or about 0.022654 AU, I will give this a shot though 3 million miles is awfully close to a G type star.

Cheers.

[Apollo7]

Incidentally, at the small distance required by your suggestion the ambient temperature is 1670 K, which is over 1300 C, the planet is tide locked but wouldn't such an inferno make the small world essentially a ball of lava?

[Cormoran]

Umm, Just an observation, but I though Io was way it was due to tidal stresses from Jupiter AND the other galilean moons.

I look forward to being corrected, as Apollo7's world sounds like a wild and wacky (not to mention visually interesting) place.

Cormoran

[Apollo7]

You are quite right Cormoran, Io is kept molten due to tidal forces. However I do not believe that in order for a planet to be "Io-like" that it must necessarilly have vulcanism driven by massive tides. The gist was simply that the planet be turning itself inside out on a regular basis.

Now if you consider that this world, would have a day-side temp of 1670 K and a night side temp of 90 K, you can imagine the interesting situations this might create. If I recall convection plays a big part in circulation of hot magma in the Earths mantle, I can only wonder how convection would impact a sea of lava. obviously your not going to have one side of the planet totally molten and one side totally solid, but there might be a situation analagous to calving of iceburgs, only it would involve large pieces of stone floating into the magma-sea. Of course this is wild speculation, but interesting none the less.

Any further ideas?

[Cormoran]

This is weird. All I can see is this solid crust extending out from the cold pole, gradually thinning and softening in the direction of the hot-pole, until under the continual burning eye of the sun (Sauron, anyone?) the crust is little more than calving blocks of pumice floating on a thick molten slurry. I would assume that this world has no atmosphere to speak of given its proximity to its primary, but I can imagine planting a base on the cold pole, and running cables sunward to exploit the temperature differential for power generation.

The weird bit was the fact that it all made me think in terms of a partially-baked spongecake Not wishing to ruin the previous image, of course.

Thats gonna be a weird looking map, but I'm really looking forward to seeing it

Cheers,

Cormoran

[Apollo7]

Well the planet has a trace atmosphere from outgassing, but little more than that, it gets replenished through the vulcanism and so is rarely totally devoid of an atmosphere, although like with mercury, I would imagine on the whole particle colissions in the tenuous atmosphere would occur more often with the surface than with neighboring particles.

well I could invision an ice encrusted night-side with little to no solid surface on the daylit-side but, there is some question as to the stability of such a surface. I would think that there would be alot of crustal shifting, although over time the dark-side crust could become very thick and strong, the crust facing the star would be very viscus and thin.

If anyone has seen the movie Star Trek III one might remember the case of the Genesis Planet and its inevitable destruction. I can imagine one side being Genesis Post-instability type with massive calderas and lava flowes and the other being more like Mars with ice below the surface and above, probably brought in by comet impacts and the like. Perhaps the crust gets progressively thinner towards the subsolar point, and eventually is reduced to a lake of molten slag, measuring a hundred miles in diameter or some such, like a giant red eye. That would be interesting.

[Evil Dr Ganymede]

You are quite right Cormoran, Io is kept molten due to tidal forces. However I do not believe that in order for a planet to be "Io-like" that it must necessarilly have vulcanism driven by massive tides. The gist was simply that the planet be turning itself inside out on a regular basis.

Now if you consider that this world, would have a day-side temp of 1670 K and a night side temp of 90 K, you can imagine the interesting situations this might create. If I recall convection plays a big part in circulation of hot magma in the Earths mantle, I can only wonder how convection would impact a sea of lava. obviously your not going to have one side of the planet totally molten and one side totally solid, but there might be a situation analagous to calving of iceburgs, only it would involve large pieces of stone floating into the magma-sea. Of course this is wild speculation, but interesting none the less.

Any further ideas?

1670K is hot enough to melt pretty much any silicate rock. And blocks of silicate rock would sink in its own melt - it's only water ice that floats in its molten form. And also, the dayside temperature won't be uniformly 1670K will it?

Anyway... A G4 V star could be young, if it's about 0.95 solar masses (stars change spectral type as they get older). It should have a luminosity of around 0.85-0.90 Sols. Problem is I don't know what the albedo of a molten planet ought to be. If I assume it's 0.5, then your planet at about 0.09 AU only has a blackbody surface temperature of about 750K. If it's at 0.02 AU then its temperature goes up to 1890K. But at the latter temperatures, the minimum molecular weight that the planet can hold onto is about 320, which means that some of the lighter rock forming minerals (eg quartz) evaporate and are lost into space!

[Apollo7]

I realize that only ice floats in water, however when I realized what I had said I was too lazy to come back and correct myself. On the other hand lead will float in Mercury, so there are always other possibilities. Anyway, I shifted the planet out to .04 AU, where the temperature is more or less 1000K, .02 felt way too close for me.

uniform temperature is unlikely in any event of course. Albedo for a molten surface is something I had not thought about, but that is an interesting question, like the albedo of the Earth when it was a molten rock sailing through space. Perhaps it would be in the .4 to .6 range. In any case I've wondered if the planet would endure both a solid and molten side, or would there be forces at work that would prevent such a situation from occuring.

So now I have a temperature range of 900-1100K, planet is tidally locked, period of a few days, trace atmosphere, although where pockets of outgassing occurs the pressure would be much higher, but still highly localized.

I can imagine a planet with a frozen dark-side and molten light-side would be incredibly unstable, but I wouldn't know how exactly that would effect the evolution of that world.