Jump to content

Solution to the minmus paradox


Newgame space program
 Share

Recommended Posts

It's not about atmosphere. Given proximity to Kerbol, Minmus is too hot for ice. Even if it's cooled by sublimation of said ice, it'd disappear entirely too fast. And it cannot be replenished by external sources, as that would generate additional heat. In short, icy Minmus just isn't possible. But I do like glassy Minmus solution.

Link to comment
Share on other sites

Another thing to consider is that it doesn’t matter how much heat minmus receives from kerbol, as long as it can radiate enough of it to stay icy. With that much reflection a lot of the energy is already deflected similar to how our own ice cpas can stay solid in the summer by not absorbing too much energy, and as the planet rotates it can radiate excess heat on the night side. 

Link to comment
Share on other sites

ok but what if it wasnt water ice but something else ice. I know blending salt with ice melts it quicker but what if there was a sort of oposite material that makes ice have a higher melting point. and if there isnt just make one up just like kerbals arent made of an existing material. 

Link to comment
Share on other sites

8 hours ago, t_v said:

as long as it can radiate enough of it to stay icy.

That's a sensible explanation of KSP1's Minmus.

The equilibrium temperature of Minmus would be around −20°C, given that the Kerbal system is scaled so Minmus receives as much solar flux as does Earth.
(The simple computations of radiative equilibrium ignore the less-than-perfect emissivity  of planets, but in fact water-ice does in fact have over 90% emissivity for thermal infrared light.)

Daytime Minmus would get warmer, night-time colder, but Minmus rotates pretty quickly so maybe it will stay below freezing all day.

The trouble is, ice evaporates, faster as the ice is warmer, so it is hard to believe ice on Minmus could last very long. (Unlike comets, who spend most of their time far from the sun.)  Minmus's gravity can't hold the vapour leaving the ice every day, so in a couple thousand years you would think it would be dry rock.  

Imagining the formation of smooth fields of ice is also tricky, but fun.  Maybe another moon fell into young Kerbin and the heat very briefly melted Minmus's ice.

Edited by OHara
thousand years was a thousand times too generous
Link to comment
Share on other sites

34 minutes ago, jastrone said:

ok but what if it wasnt water ice but something else ice. I know blending salt with ice melts it quicker but what if there was a sort of oposite material that makes ice have a higher melting point. and if there isnt just make one up just like kerbals arent made of an existing material. 

Weell have you seen the video? They've tried every possible combination and couldn't keep the whatever ice in place. Not at this distance from the star.

In any case, we always have Vall, which is much more icy.

Link to comment
Share on other sites

Hold on a moment, I think I disagree with the assessment that water couldn’t remain frozen on minmus. (By the way, I have nothing against glass, I also think it’s cool.) on our own planet, the only reason we have liquid water in our surface at all is because the atmosphere keeps it warm by trapping heat. With our own moon, there are ice caps on the poles which don’t really melt even in summer, because they can reflect enough energy. Minmus, with such a high surface area to volume ratio, would be able to easily dissipate heat and stay frozen. Space is really really cold and even if you were in the sun, without insulation you would freeze. So minmus, which has no atmospheric insulation, would never get the chance to thaw out. 

Link to comment
Share on other sites

14 minutes ago, t_v said:

Minmus, with such a high surface area to volume ratio, would be able to easily dissipate heat and stay frozen.

True, but for the same reason the sun can also heat it up easily.  Solar radiation at Earth's (or Kerbin-Minumus's) orbit is about 1kW/m², which turns out to be enough to heat the surface of the Moon quite warm in the daytime.  In unprotected space, the side facing the sunshine gets rather hot.

(And, ice evaporates, slower in the cold, but it needs to be very cold to stay around for years.)

Link to comment
Share on other sites

2 hours ago, pandaman said:

Just a thought here, but glass melts.  Therefore solid glass is just 'frozen' molten glass. 

Solved. :D

You could say the same about (sorry) hydrogen. Solid, in other words metallic is "just" frozen liquid hydrogen. Totally omitting other requirements on purpose :)

It's all about temperature you want to keep something at, eh?

I know, jokes

Link to comment
Share on other sites

20 hours ago, t_v said:

on our own planet, the only reason we have liquid water in our surface at all is because the atmosphere keeps it warm by trapping heat.

That's also very true, and interesting to think about.

The equilibrium temperature of a bare Earth would be 255K = −18°C.   (If Earth was covered in snow and ice, it would reflect more of the mostly-visible light from the sun, but snow is not so white thermal infrared, so it would emit infrared reasonably well and make the equilibrium temperature even colder.)

Some ice would evaporate into water molecules with thermal velocities averaging 540 m/s, which is well below Earth's escape velocity (as well as Kerbin's, but enough to escape Minmus).

The evaporation would build up an atmosphere of water vapour, until the rate of re-condensing matches the evaporation rate, which happens the vapour pressure at the surface is about 100 Pa = 1 millibar.

Water vapour is itself a greenhouse gas, because the H-O-H bending vibrations absorb thermal infrared light (the same reason that snow emits significantly for radiative cooling).  So you might think that the atmosphere would become opaque to outgoing thermal radiation.  Then the planet would come to equilibrium where the upper atmosphere, at the average level visible from space in the thermal infrared, is at 255K.  The surface could be warmer, because the vapour is warmed by gravitational compression whenever convection moves it to lower altitudes.

But the small amount of water vapour in equilibrium over an icy earth isn't enough to make the atmosphere opaque, so the equilibrium surface temperature would remain around 255 K.  The prehistorical possibility of a snowball Earth (far, far prehistorical) seems plausible, and would seem difficult for Earth to have escaped. 

So assuming Kerbin-Minmus is imagined to receive the same solar flux as Earth (and I think that is the intention) Minmus would be cold enough for ice, but with insufficient gravity to hold on to what evaporates away.

Link to comment
Share on other sites

18 hours ago, The Aziz said:

You could say the same about (sorry) hydrogen. Solid, in other words metallic is "just" frozen liquid hydrogen. Totally omitting other requirements on purpose :)

It's all about temperature you want to keep something at, eh?

I know, jokes

Sorry but that's not quite right. Solid hydrogen is just hydrogen ice, which is just a matter of keeping the hydrogen at a low enough temperature. Metallic hydrogen is like diamonds, in that you need both the required temperature AND ALSO very very very high pressure. And of course, according to our best knowledge on metallic hydrogen, as soon as you release that pressure the hydrogen will return to it's normal "solid" state, instead of staying metallic (that part where metallic hydrogen isn't stable at lower pressures is the whole reason why several people on the forums have very vocal opinions against rocket engines using metallic hydrogen). Anyways, enough about metallic hydrogen, let's get back on topic of making Minmus be a ball of mostly ice, right where it is in its orbit (both around Kerbin and around Kerbol).

I have a different idea that would make it easy to have Minmus be icy year-round no matter what. But it's not about changing anything about Minmus.
The whole Kerbal star system is scaled down roughly 10x from the IRL Earth's solar system, right? What if it's ACTUALLY that small, and not just "small for gameplay reasons"?
That would mean that the STAR that Kerbin's around would have to be smaller, right? Smaller stars that are in their main phase of life (where they're fusing Hydrogen to Helium) are much smaller (EDIT: Cooler), so that would mean that Kerbol is actually a smaller (EDIT: again, I meant cooler) star than earth's Sun.
That would by default make Kerbol not a G-class star (which is what Earth's Sun is).
So, if Kerbol's a smaller star, it would be cooler. Not sure where it would land exactly, but it would probably end up as either an M-type star, or even a brown dwarf, either of which are barely sustaining a fusion reaction and therefore are the longest-lived but also COOLEST stars (temperature-wise and output power wise).
Put Kerbin (and therefore Minmus) around a Type-M or Brown Dwarf star, at it's current orbital altitude, and I'm pretty sure that Minmus being made of ice would have no problem staying icy whatsoever.

The only problem is that the spectrum of the star isn't redder than our star, at least according to the eyes and cameras of the Kerbals.
I have an explanation for that too. The eyes of the Kerbals are adapted to the output spectrum of the cooler star, so what they think is "white" light, and what they think is the "visible spectrum" of light, might not be the same as what we've defined to be the "visible spectrum" of light, since that's based on OUR HUMAN EYES and not Their "Kerbal" eyes.
Because of the cooler emission spectrum of the smaller star, Kerbals would probably be able to see significantly into the Infrared wavelengths, along with the plants also having photosynthetic cell mechanisms that operate on longer-wavelength photons than the reds and yellows and greens (not so much blues) of Earth plants. They might not even have a cone cell type that's sensitive to what we perceive as "blue" light (or whatever they use for photo-receptors, who knows, Kerbals have literally nothing biologically in common with Humans).
Basically the issue becomes that image data they generate for their own use would be tailored to the colors of light that their eyes are sensitive to, which thanks to evolution would most likely be the light wavelengths that make their way thru Kerbin's atmosphere the easiest. And if Kerbol isn't a G-type star, then the range of wavelengths that Kerbal eyes are sensitive to would NOT be the same as the range of wavelengths the Human eye is sensitive to.
As for why Kerbin has liquid oceans and Minmus isn't a melting iceball, well Kerbin might have an atmosphere with a lot more greenhouse gases in it than Earth's atmosphere, therefore artificially raising the surface temperature to something similar to Earth's surface temperature.

So, to sum it up, Minmus might be made of ice if Kerbol is in fact a smaller star and the Kerbal eyes are adapted to that spectrum instead of our Sun's spectrum so Humans and Kerbals don't agree on what color is what, which is why everything looks fine to us playing KSP.

Edited by SciMan
Link to comment
Share on other sites

My headcanon was that it was salt, hence the terrible taste. Glass would not be delicious, but it would probably be a more neutral taste (John Young reported that Moon dust didn't taste half bad)

Salt might also be able to explain how the flats formed - perhaps if Minmus was a fragment of an early icy planet, and there were some layers of ice or water underneath that vaporized as Minmus approached the Sun, and now there is almost entirely only salt left.

Edited by cubinator
Link to comment
Share on other sites

15 minutes ago, AtomicTech said:

@Minmus Taster, you're going to have to pay a visit to the name change thread to become Vall Taster.

  Reveal hidden contents

Please don't make the mistake of naming yourself to "Val Taster".

 

No no, the name still stands, even better then before actually, I like eating glass :)

 

Link to comment
Share on other sites

On 10/31/2021 at 8:59 AM, t_v said:

Minmus, with such a high surface area to volume ratio, would be able to easily dissipate heat and stay frozen.

That's not how it works. At relevant time scales, more than a few meters of rock might as well be perfect insulation, so the surface can be considered as a infinite flat plane in equilibrium with stellar flux and background of the cosmos for purposes of thermal analysis. While the average surface temperature without greenhouse gasses and with high albedo can be bellow freezing, without atmosphere you also have very high fluctuations between day and night, and day high is going to be about 70% above average equilibrium, which is way, way beyond the freezing temperatures.

Yes, near poles, situation is different. Stellar flux incidence angle is very low and it's possible to have regions of near permanent shade. But Minmus has "ice" lakes in equatorial regions. That's flat out impossible by a margin that's not even close.

Link to comment
Share on other sites

It's a heat sink below the ice.

It sucks out the solar heat and keeps the surface frozen.

The heat either warms something with extremely high heat capacity or gets teleported to another body (say, into Jool).

Maybe there was a local wormhole into the Jool atmosphere, it attracted the water molecules and the snowflakes, so the Minmus is a snowball obstructing the wormhole to Jool.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...