# A probe floating in Sun's surface

Is it possible to construct a probe that would float in the Sun's surface?

The temperature of Sun is 5,800 K and I heared there are alloys that can remain solid at 4500 K.

I wonder if it is possible to develop a better material or use an internal cooling system to keep the shell below the melting point. And have the internal volume filled with light material or vacuum so that it would float.

• First, there's no surface. Second, it isn't possible with today's technology. Oct 12 '15 at 5:01
• I'm voting to close this question as off-topic. It requires some basic physics to be learned first, to understand why the question does not make sense. Oct 12 '15 at 8:05
• It is about Space exploration. If we keep being pedentic, half the questions here should go on physics, or astronomy sites. Oct 12 '15 at 14:14

Thermodynamics says there's no such thing as a completely internal cooling system. The best you can do is pump heat to a cooler location. That's very difficult to come by in the photosphere. Besides trying to keep cool enough for some alloy to remain solid, keeping electronics or a power source cool enough to function would be significantly more difficult.

Also, the photosphere is quite rarefied. It has a density similar to the earth's atmosphere at an altitude of about 60km. That's above the level where even high-altitude balloons travel. So even if the cooling problems weren't there, "floating" at that level with equipment isn't possible.

• Note: the current world record for unmanned balloons is 53.0km, set in 2002. That would indeed be quite challenging to surpass by 5-10km with the additional weight of high-temperature materials. Oct 12 '15 at 22:18
• Would the Sun heat a probe built out of dark matter, or is "cold" in CDM just an analogue concept to the temperature of baryonic matter? Oct 13 '15 at 3:56
• @LocalFluff Dark matter does not absorb or emit light or interact kinetically with normal matter, so the Sun would not heat it. We don't know enough about dark matter to construct a probe from it though. Oct 13 '15 at 16:43
• @LocalFluff Also, since it does not absorb or emit light, you couldn't really use standard communications for interacting with such a probe. Oct 13 '15 at 16:44
• @jwenting There is very good evidence to account for the existence of something that we call "dark matter". What exactly that phenomenon is is still in question, but there are alternative theories, as you allude to. None of them have yet managed to explain all the evidence. Jul 19 '19 at 13:10

There's an alloy that will just barely be solid even at the temperature at the sun's surface. If you could make a sufficiently low density foam out of it you might be able to construct something that would float. Given how close to it's melting point it would be I would be very surprised if it would remain a foam, though.

Since you have only one element to work with it would be a pretty useless probe, though.

Firstly, as the comments said, there is no solid surface on the sun. It's a big ball of plasma which undergoes fusion (process of atoms combining and releasing energy). Secondly, an object can't "float" on the sun. A possible but very unlikely theory would be to have a probe that floats because of convection. Constant heat acting on the bottom of it and colder areas coming down (similar to how birds use warm air to rise), however it needs to overcome the Sun's gravity and convection only occurs in the convection zone which makes it impossible. Another possibility is to create a probe that continuously fires its thrusters to stay afloat. But this is useless and uses a lot of fuel. Your best bet would be to make a probe that orbits the Sun, however that is also very hard to do for many reasons. First, you need to get to the Sun. Most probes go into the outer solar system (such as Jupiter) to use a gravity assist to slow down and orbit close to the sun, similar to the Ulysses spacecraft. This is the trajectory of the Ulysses Spacecraft (note how it uses Jupiter to slow down). Also, in order to orbit that close to the sun, you need tremendous orbital velocity. You can calculate how much orbital velocity is needed with the Vis-Viva equation.

These are just ways to get close to the Sun, another big problem is to use a material that can survive the intense heat, and electromagnetic radiation. However there is an advantage, heat is not the same as temperature. Heat is the amount of energy transferred while temperature measures how much the particles move. Here's an example, a cup of boiling water and a tub of boiling water are both 100 degrees Celsius, however the tub has more heat energy because it has more mass (molecules) even though they're both the same temperature. Same applies to space. Space is virtually a vacuum so there are very few particles thus your spacecraft can survive. This is how the Parker Solar Probe survives the heat of the Sun. As for thermal radiation, it's a method of heat transfer that doesn't require a medium and travels through waves in a straight line. A workaround through that is to have a reflective shield that reflects the radiation and prevents it from travelling to the other side of the shield similar to the previously mentioned Parker Solar Probe.

• you forget one thing here: it's not just heat transfer from impacting particles that increase the energy levels (and thus temperature) of your spacecraft, it's radiation as well. Away from the sun your probe can cool itself using radiator fins, the probe OP wants that sits inside the sun's atmosphere at all times doesn't have that luxury as the fins could never cool it to below the ambient temperature of its environment. Jul 19 '19 at 8:35
• @jwenting Yes, thank you. Radiation is how heat is transferred to Earth, planets, or anywhere far from the Sun's atmosphere (corona). But radiation is the least efficient method of heat transfer (similar to how putting your hand on a stove hurts more than putting your hand above it).It can be solved by putting a reflective shield meaning heat radiation would not transfer to the other side of the shield as radiation goes in a straight line. Similar to the Parker Solar Probe I mentioned. However your comment reminds me of something else I forgot. Ionizing radiation such as solar flares and etc. Jul 19 '19 at 14:42

Is it possible to construct a probe that would float in the Sun's surface?

The surface of the Sun is well defined, and can be found somewhere within the Sun's photosphere at the point where the optical depth reaches about 2/3.

According to sources in the as-yet unanswered question What is the density profile within the Sun's photosphere? Which one of these is wrong? the density at this point is either 1E-06 g/cm^3 which is a thousand times lower density than air or aerogel, or a thousand times lower than that!

I'll update this as soon as that question is answered.

From this answer here is a plot of the Sun's density versus depth.

and from the raw data cited in that answer we can see that even if we look for the density of air, were half way to the center of the Sun at a temperature of 3 million Kelvin.

You can't make a balloon or evacuated chamber, because the pressures anywhere near where there is high enough density to support an extremely low density floating craft is way too high.

This just won't work.