Nothing beats digging out the ice compresses from the freezer coming home from the hot summer. While packing them around my neck, I thought of being an enormous Michelin Man in an ice cube suit, and, well, the rest is OP. Say I’m just there, as close as possible as the ice will protect me in a normal NASA space suit, and need to stay alive for one second.
I know about the Leidenfrost effect (water skitters on hot pan)… Does that make any sense whatsoever in this regime?
Will I/my planetary-size (?) ice-flow “sink?” What is the surface of a star, anyway?
3a) I don’t “sink” through my chair, the earth, etc., because of electromagnetic force force, right? Other atomic forces are practically infinitesimal here, but on a sun-like star, let alone neutron stars…?
To lower the necessary amount of ice, let’s assume I’m doing this at night.
I think structural stability is going to be a concern long before the heat issue. I don’t know that moon sized chunk of pure water ice is going to have all that much structural integrity period and who knows what the sun’s gravity will do to it as you approach.
One possible problem is that if you’re going to be that close to what is essentially highly radioactive plasma, thermal radiation is probably going to be the least of your worries. If you were close enough to anything resembling a solid surface, or even a gaseous one, you’d probably end up as irradiated as a Kwiki-Mart burrito.
I know water is used to damp nuclear reactions, but ice has a crystalline structure and might not be as effective at catching high energy particles.
Anyway, if you want some empirical data, for what it’s worth, Comet ISON in 2013passed approximately 724,000 miles above the sun’s surface and disintegrated. It was estimated to have been between .8 and 2 kilometers in diameter. So there are some practical difficulties in even getting close enough to the sun’s surface to attempt floating. But I’d start with 2.5 kilometers of ice and work up from there.
For an interesting take on this concept, see Theodore Thomas’ The Weather Man (included in the Arthur Clarke anthology, Time Probe). This story postulates control of Earth’s weather by manipulating reactions on the surface of the Sun. The solar boats are protected by vaporizing a thin layer of carbon instead of water ice. A classic of the field, uniting the political, scientific, and technical resources used to make it all happen.
For a really rough approximation, I envisioned a block of ice with a bottom surface area of 1 square meter, parked on the sun.
Surface of the sun is a blackbody at T=5000K, so at close range it’s directing 35.4 MW at the face of the ice block.
For simplicity, I assumed the ice/water absorbs all of this power, and needs to be sublimated. Heat of sublimation for water is 2.8x10[sup]6[/sup] J/kg, so this scenario would be sublimating 12.6 kg of ice per second. a slab of ice 1 meter square weighing that much is only 1.3 centimeters thick, a little over half an inch.
This scenario neglects the non-unity absorptivity of water/ice, but it also neglects conductive/convective heat transfer; I’m at a loss for how to estimate those for the stuff that is expelled from the sun. It also disregards any protection you’d need during the time it takes for you and your ice shield to travel to this location. You’d also need a much wider/longer slab, or one with tall sides, in order to completely shield you from a direct view of the rest of the surface of the sun.
According to Wikipedia, the density of sun-stuff is an average of 1.4 g/cm[sup]3[/sup]. It’s much higher than this at the sun’s center, which means it’s much lower than this at points far from the center. “Surface” is going to be impossible to pinpoint, but there’s surely some distance from the center at which your ice cocoon will achieve neutral buoyancy and cease its descent. You would need it to be completely sealed; an open-topped ice canoe will allow less dense solar matter to spill over the gunwales as you descend to the neutral-buoyancy depth.
Anyway, yeah, I’m going with a minimum of 1/2" of ice to survive for one second on the “surface” of the sun.
The problem with saying that the density of the Sun is 1.4 g/ml, and that therefore ice would float on the Sun, is that the Sun is under enormous pressure. The Sun is mostly made of hydrogen, to get hydrogen denser than water requires enormous pressure. So your ice shield isn’t going to float for long, since most of the mass of the ice is oxygen it’s going to be much denser than the hydrogen.
I suppose the Sun would have to boil the ice into plasma before it could compress the resulting mass to the average density of the Sun.
Interesting point. I don’t know what kind of pressure is required to get hydrogen up to that density, except to say it’s surely a lot. And I don’t know what happens to the density of ice under that kind of pressure, but even if it stays at constant density, it’s unlikely that you could design an ice-walled pressure vessel that would hold up. Ice will actually flow when the stress is high enough; I expect you’d have to have an insanely thick-walled ice vessel to prevent your interior life-chamber from slowly collapsing down to a tiny meat-filled pore.
For one second? The sun’s highest “surface” layers are hot, but they’re also very diffuse. It’s like putting your hand into an oven at 400 degrees. Because air has such a low density, your hand doesn’t get burned in one second… or even in many seconds. It takes minutes to accumulate real damage.
By the time you have something dense enough to “stand” on (more like float in, once you reach a matching density), you’ve already burned up. That’s more like touching the metal wall of the oven. At the same 400 degrees, one full second of contact puts you on your way to the burn ward.
Xema, I figured somebody would be quick to point out my source, and, as I just checked, my error: Ali G suggested you had a better chance of walking on the Sun in winter, when it definitely would be lots cooler, than at night.
Here’s another fun fact: The solar corona, which extends many times the radius of the photosphere, has a temperature of millions of degrees, a thousand or so times the temperature of the photosphere. And yet, if you were in a spacesuit in the corona, with a heat shield directly beneath you to shade you from the photosphere, you would freeze to death. The corona is so diffuse that you’d lose more heat radiatively to deep space than you would gain via conduction from the corona.
We think of solids and liquids as incompressible, and that’s true, at the sorts of temperatures and pressures we’re used to. But hydrogen nuclei in the Sun are so compressed that it supports nuclear fusion. That’s really compressed.
Even if the Sun was room temperature instead of thousands of degrees the pressure would be so great that normal solids like “ice” would be impossible.