<p>A "space knife" is a non-starter: You can't cut a plasma with a knife because it behaves like a gas, not like a solid. You can't put anything into the sun or go anywhere near it because it is hot enough to vaporise <em>anything</em>. Any concept that involves "flying over the surface and scooping up hydrogen" is not going to work. </p>

<p>Getting close to the sun is hard. You are orbiting the sun at 30km/s If you want to get close to the sun, you will need to slow down a lot that requires a lot of fuel. Then to get away from the sun you will need to speed up again. This takes a lot more fuel, far more than you could hope to gather from the sun.</p>

<p>It is possible to collect some hydrogen without going anywhere near the sun.
You can collect hydrogen and helium from the solar wind. The sun blows plasma off its surface and this could be collected using magnetic fields.  This "wind" is not very dense: about 3-6 atoms per cm³. So you need to scoop a very large region for a long time to get a reasonable amount of gas. This gas is hot (36000 degrees) charged (its a plasma) and diffuse.</p>

CC BY-SA 3.0
2018-02-28T12:12:25.120Z
Your orbital mechanics are off -- a parabolic or hyperbolic flyby, with the "slingshot" effect to gain speed, will let you get nice and close.
Carl Witthoft
CC BY-SA 3.0
2018-02-28T18:20:40.893Z
The delta v to to from a circular orbit to parabolic one are substantial.
James K
CC BY-SA 3.0
2018-02-28T20:22:44.063Z
OK, -- I wasn't requiring that we start out from Earth.
Carl Witthoft
CC BY-SA 3.0
2018-02-27T15:52:59.153Z
2018-02-27T15:52:59.153Z
James K
<p>We do not have, so far, have the technology to gather the Suns resources, besides Solar Panels here on Earth. A Dyson's Sphere is a theorized technology that could be able to harness the Suns energy. I am sure NASA is working on a solution, but at 5600 Deg. Celsius / 10,000 Fahrenheit, not even titanium can withstand a Close Encounter with our closest star, much less grabbing a piece of it. The <a href="https://www.nasa.gov/content/goddard/parker-solar-probe" rel="nofollow noreferrer">Parker Solar Probe</a> is a planned mission to the Sun, in the Summer of 2018. The probe is supposed to approach the Sun and orbit 3.67 million miles from the surface. We will have to see if it lasts very long. We will have to see!</p>

CC BY-SA 3.0
2018-02-27T12:41:01.523Z
Really has little to do with the question asked.
ProfRob
CC BY-SA 3.0
2018-02-26T18:04:38.490Z
2018-02-27T08:28:38.777Z
2018-02-27T08:28:38.777Z
user21598
<p>The idea of removing material from the sun for either fuel or to lengthen its lifespan is called "<a href="https://en.wikipedia.org/wiki/Star_lifting" rel="noreferrer">star lifting</a>". Various hypothetical methods have been suggested, including heating parts of the atmosphere or squeezing it using magnetic fields. My own tentative suggestion is to combine these with chaos control to manipulate turbulence into making coronal mass ejections in desired directions. </p>

<p>The problem is not just that the sun is hot (5777 K at the surface), but that the stuff that is easy to scoop up with a huge magnetic field is a fairly sparse plasma - you don't get that much material despite the vast scales. Of course, you may want to compress the plasma into a smaller and more convenient ball, but now the ideal gas law tells you that it will heat up proportionally - to get a cool hydrogen ball you will need to bleed off all that heat slowly. </p>

<p>Which is why I think Dyson spheres are probably the easiest way to start. </p>

CC BY-SA 3.0
2018-02-26T21:41:51.527Z
I'm going to wait until tomorrow but this is a not unreasonable answer on the practicalities while ignoring the fantastical aspect of my question. Good stuff.
Kevin Teljeur
CC BY-SA 3.0
2018-02-27T09:42:48.280Z
I'm going to accept this as the most reasonable answer that I can work with. Thanks - now to try and format this for my daughter! This isn't exactly the Stack site which is most amenable to humour, is it?
Kevin Teljeur
CC BY-SA 3.0
2018-02-27T15:44:59.270Z
@KevinTeljeur - Thanks. Reformulating physics for kids is a fascinating topic on its own. That is where you actually get to see if you have understood it yourself. Good luck!
Anders Sandberg
CC BY-SA 3.0
2018-02-26T19:50:30.010Z
2018-02-26T19:50:30.010Z
Anders Sandberg
<p>Bear with me. I want to explain this to my 6 and half year old.</p>

<p>If, all things being equal, we could reach out to the Sun with a suitable implement, a gigantic space knife, could we cut a piece off the Sun? Take a slice from it? Do we end up with a body of Hydrogen and Helium, or is it impossible to extract anything from it?</p>

<p>I know that the Sun is a massive ball of plasma, the sheer mass compressing the gas through gravity until fusion is achieved. What I have been asked is, effectively, what happens if you try to take a piece of that plasma? Of our sun? </p>

CC BY-SA 3.0
2018-02-26T19:17:41.867Z
I'm voting to close this question as off-topic because this is not really astronomy but a rather odd "what if" question.
StephenG - Help Ukraine
CC BY-SA 3.0
2018-02-26T19:19:22.140Z
Fair enough. I was hoping for an actual, genuine answer - there isn't any other group of experts on this topic!
Kevin Teljeur
CC BY-SA 3.0
2018-02-27T15:45:49.087Z
It is a physics question, but the physics of stars is pretty much ignored by all but the astronomy and astrophysics communities, so I'd like to keep it open here.
Carl Witthoft
<the-sun><space><hydrogen><helium>
Can I slice off a piece of the Sun?
Kevin Teljeur
# Can I slice off a piece of the Sun?

(Asked by: username_0 on 2018-02-26)

Bear with me. I want to explain this to my 6 and half year old.

If, all things being equal, we could reach out to the Sun with a suitable implement, a gigantic space knife, could we cut a piece off the Sun? Take a slice from it? Do we end up with a body of Hydrogen and Helium, or is it impossible to extract anything from it?

I know that the Sun is a massive ball of plasma, the sheer mass compressing the gas through gravity until fusion is achieved. What I have been asked is, effectively, what happens if you try to take a piece of that plasma? Of our sun?

**Tags:** the-sun, space, hydrogen, helium
> **Comments:**
> **username_1**: I'm voting to close this question as off-topic because this is not really astronomy but a rather odd "what if" question.  
> **username_0**: Fair enough. I was hoping for an actual, genuine answer - there isn't any other group of experts on this topic!  
> **username_2**: It is a physics question, but the physics of stars is pretty much ignored by all but the astronomy and astrophysics communities, so I'd like to keep it open here.  

---

## 3 answers

### Answer by username_6 on 2018-02-26. Score: 7 | Accepted answer

The idea of removing material from the sun for either fuel or to lengthen its lifespan is called "[star lifting](https://en.wikipedia.org/wiki/Star_lifting)". Various hypothetical methods have been suggested, including heating parts of the atmosphere or squeezing it using magnetic fields. My own tentative suggestion is to combine these with chaos control to manipulate turbulence into making coronal mass ejections in desired directions.

The problem is not just that the sun is hot (5777 K at the surface), but that the stuff that is easy to scoop up with a huge magnetic field is a fairly sparse plasma - you don't get that much material despite the vast scales. Of course, you may want to compress the plasma into a smaller and more convenient ball, but now the ideal gas law tells you that it will heat up proportionally - to get a cool hydrogen ball you will need to bleed off all that heat slowly.

Which is why I think Dyson spheres are probably the easiest way to start.

> **Comments:**
> **username_0**: I'm going to wait until tomorrow but this is a not unreasonable answer on the practicalities while ignoring the fantastical aspect of my question. Good stuff.  
> **username_0**: I'm going to accept this as the most reasonable answer that I can work with. Thanks - now to try and format this for my daughter! This isn't exactly the Stack site which is most amenable to humour, is it?  
> **username_6**: @KevinTeljeur - Thanks. Reformulating physics for kids is a fascinating topic on its own. That is where you actually get to see if you have understood it yourself. Good luck!  

---

### Answer by username_3 on 2018-02-27. Score: 1

A "space knife" is a non-starter: You can't cut a plasma with a knife because it behaves like a gas, not like a solid. You can't put anything into the sun or go anywhere near it because it is hot enough to vaporise *anything*. Any concept that involves "flying over the surface and scooping up hydrogen" is not going to work.

Getting close to the sun is hard. You are orbiting the sun at 30km/s If you want to get close to the sun, you will need to slow down a lot that requires a lot of fuel. Then to get away from the sun you will need to speed up again. This takes a lot more fuel, far more than you could hope to gather from the sun.

It is possible to collect some hydrogen without going anywhere near the sun.
You can collect hydrogen and helium from the solar wind. The sun blows plasma off its surface and this could be collected using magnetic fields. This "wind" is not very dense: about 3-6 atoms per cm³. So you need to scoop a very large region for a long time to get a reasonable amount of gas. This gas is hot (36000 degrees) charged (its a plasma) and diffuse.

> **Comments:**
> **username_2**: Your orbital mechanics are off -- a parabolic or hyperbolic flyby, with the "slingshot" effect to gain speed, will let you get nice and close.  
> **username_3**: The delta v to to from a circular orbit to parabolic one are substantial.  
> **username_2**: OK, -- I wasn't requiring that we start out from Earth.  

---

### Answer by username_4 on 2018-02-26. Score: 1

We do not have, so far, have the technology to gather the Suns resources, besides Solar Panels here on Earth. A Dyson's Sphere is a theorized technology that could be able to harness the Suns energy. I am sure NASA is working on a solution, but at 5600 Deg. Celsius / 10,000 Fahrenheit, not even titanium can withstand a Close Encounter with our closest star, much less grabbing a piece of it. The [Parker Solar Probe](https://www.nasa.gov/content/goddard/parker-solar-probe) is a planned mission to the Sun, in the Summer of 2018. The probe is supposed to approach the Sun and orbit 3.67 million miles from the surface. We will have to see if it lasts very long. We will have to see!

> **Comments:**
> **username_5**: Really has little to do with the question asked.  

---

