<p>I can't get an exact answer, but I think I can make a &quot;Fermi&quot; estimate.</p>
<p>First let's consider what would happen without the sun.  The water, at 20 degrees, will boil in a vacuum. Now boiling in microgravity is weird.  Since bubbles don't &quot;rise&quot;.  You can see some <a href="https://science.nasa.gov/science-news/science-at-nasa/2001/ast07sep_2" rel="nofollow noreferrer">experiments on microgravity boiling</a> and note that bubbles appear in the water, and join together by surface tension.  <sub></sub></p>
<p>So one thing to ask is &quot;is the water in free fall above the sun (and so in microgravity) or is it held in place (and so experiencing rather strong gravity).  It will make a big difference.</p>
<p>In space, without the sun, the boiling water will require energy, which will rather rapidly cool the water to its triple point, (very close to freezing point) and then it will be simultaneously freezing and boiling. Let us imagine that the water is created in a sphere that is sufficiently far from the sun to be in a vacuum and heated only by radiation, and is free-falling so is in microgravity.</p>
<p>Now close to the sun, the water will be absorbing a lot of energy and there will be a race between the heating from absorbed radiation, the efficiency with which this heat is used to evaporate, and the resulting cooling.  The water will be absorbing hundreds of kilowatts, so boiling will be explosive. If the water isn't contained the production of bubbles of steam will break up the ball of water, which will tend to increase surface area and increase evaportion (and so also increase the cooling effect).  The conversion of water into steam also has a big difference in the absorption of heat radiation.  As you see this is a highly dynamic situation, with the water not staying in a nice sphere, getting warmer and evaporating from the outer surface.</p>
<p>So a simple answer isn't possible, nevertheless, close to the surface of the sun, each square metre has 600000 kW passing through it (luminosity of sun/area of sun) So there would be hundreds of kJ of energy passing into the,  water every second and it takes some 2200 kJ to boil a litre of water. Therefore it is reasonable to say that the water will be evaporated in &quot;<strong>seconds</strong>&quot;.  This is at best a &quot;Fermi&quot; estimate, and should indicate that it will not take minutes, nor milliseconds to for the litre of water to boil.</p>

CC BY-SA 4.0
2022-12-23T10:55:45.110Z
Can anyone find the videos that were once linked to that NASA page?  It was a mpg called "bubble0g.mpg"
James K
CC BY-SA 4.0
2022-12-23T10:55:08.890Z
2022-12-23T10:55:08.890Z
James K
<p>Assume that 1 liter of water in room temperature (20 °C) would suddenly appear next to the Sun (or maybe 1 kilometer next to it). How long would it need to evaporate?</p>

CC BY-SA 4.0
2022-12-22T09:53:29.540Z
Welcome. Can you explain to us what steps you undertook to solve this problem yourself? Also: how do you want to define the "surface" of the sun? Please see https://astronomy.stackexchange.com/help/how-to-ask - I'm missing some elaboration on the "search and research" part and somewhat also on the "why is it relevant" (other than a homework).
planetmaker
CC BY-SA 4.0
2022-12-22T10:24:41.633Z
As stands this isn't usefully answerable.  What other magic is occurring here, for example, should we suppose that the water is (somehow) at atmospheric pressure. Is the  water in a container, if not is the water kept magically in some shape like a sphere. More significantly **what will you do with this information?** Very rough estimates suggest it's going to be absorbing some hundreds of kilojoules every second, and 2500kJ will boil water on Earth at standard pressure, so "seconds" seems about right.
James K
CC BY-SA 4.0
2022-12-22T11:05:28.393Z
Valid points. I understand that the question is weird and has a lot of assumptions. I also know that there is no surface, that's why I also added the 1 km next to it. I can also Google and see that the temperature there would be around 5500°C.

Now, why do I need this? My son asked me how fast would it evaporate. So I first did a bit of Googling, then asked ChatGPT, and then asked here.
cherouvim
CC BY-SA 4.0
2022-12-22T12:34:45.843Z
Liquids aren't stable in a vacuum. On Earth, if you put room temperature water into a vacuum chamber it immediately begins to boil and freeze simultaneously, and the ice thus formed begins to sublimate (transform directly from solid to gas).
PM 2Ring
<the-sun><water>
How long would 1 liter of water need to evaporate next to the Sun?
cherouvim
# How long would 1 liter of water need to evaporate next to the Sun?

(Asked by: username_0 on 2022-12-22)

Assume that 1 liter of water in room temperature (20 °C) would suddenly appear next to the Sun (or maybe 1 kilometer next to it). How long would it need to evaporate?

**Tags:** the-sun, water
> **Comments:**
> **username_1**: Welcome. Can you explain to us what steps you undertook to solve this problem yourself? Also: how do you want to define the "surface" of the sun? Please see https://astronomy.stackexchange.com/help/how-to-ask - I'm missing some elaboration on the "search and research" part and somewhat also on the "why is it relevant" (other than a homework).  
> **username_2**: As stands this isn't usefully answerable.  What other magic is occurring here, for example, should we suppose that the water is (somehow) at atmospheric pressure. Is the  water in a container, if not is the water kept magically in some shape like a sphere. More significantly **what will you do with this information?** Very rough estimates suggest it's going to be absorbing some hundreds of kilojoules every second, and 2500kJ will boil water on Earth at standard pressure, so "seconds" seems about right.  
> **username_0**: Valid points. I understand that the question is weird and has a lot of assumptions. I also know that there is no surface, that's why I also added the 1 km next to it. I can also Google and see that the temperature there would be around 5500°C.  Now, why do I need this? My son asked me how fast would it evaporate. So I first did a bit of Googling, then asked ChatGPT, and then asked here.  
> **username_3**: Liquids aren't stable in a vacuum. On Earth, if you put room temperature water into a vacuum chamber it immediately begins to boil and freeze simultaneously, and the ice thus formed begins to sublimate (transform directly from solid to gas).  

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## 1 answers

### Answer by username_2 on 2022-12-23. Score: 3 | Accepted answer

I can't get an exact answer, but I think I can make a "Fermi" estimate.

First let's consider what would happen without the sun. The water, at 20 degrees, will boil in a vacuum. Now boiling in microgravity is weird. Since bubbles don't "rise". You can see some [experiments on microgravity boiling](https://science.nasa.gov/science-news/science-at-nasa/2001/ast07sep_2) and note that bubbles appear in the water, and join together by surface tension.

So one thing to ask is "is the water in free fall above the sun (and so in microgravity) or is it held in place (and so experiencing rather strong gravity). It will make a big difference.

In space, without the sun, the boiling water will require energy, which will rather rapidly cool the water to its triple point, (very close to freezing point) and then it will be simultaneously freezing and boiling. Let us imagine that the water is created in a sphere that is sufficiently far from the sun to be in a vacuum and heated only by radiation, and is free-falling so is in microgravity.

Now close to the sun, the water will be absorbing a lot of energy and there will be a race between the heating from absorbed radiation, the efficiency with which this heat is used to evaporate, and the resulting cooling. The water will be absorbing hundreds of kilowatts, so boiling will be explosive. If the water isn't contained the production of bubbles of steam will break up the ball of water, which will tend to increase surface area and increase evaportion (and so also increase the cooling effect). The conversion of water into steam also has a big difference in the absorption of heat radiation. As you see this is a highly dynamic situation, with the water not staying in a nice sphere, getting warmer and evaporating from the outer surface.

So a simple answer isn't possible, nevertheless, close to the surface of the sun, each square metre has 600000 kW passing through it (luminosity of sun/area of sun) So there would be hundreds of kJ of energy passing into the, water every second and it takes some 2200 kJ to boil a litre of water. Therefore it is reasonable to say that the water will be evaporated in "**seconds**". This is at best a "Fermi" estimate, and should indicate that it will not take minutes, nor milliseconds to for the litre of water to boil.

> **Comments:**
> **username_2**: Can anyone find the videos that were once linked to that NASA page?  It was a mpg called "bubble0g.mpg"  

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