<p>At the moment, the Solar System is inside the <a href="https://en.wikipedia.org/wiki/Local_Interstellar_Cloud" rel="nofollow noreferrer">Local Interstellar Cloud</a> (which is itself within the <a href="https://en.wikipedia.org/wiki/Local_Bubble" rel="nofollow noreferrer">Local Bubble</a>). The LIC has <a href="http://iopscience.iop.org/article/10.1088/1742-6596/767/1/012016/pdf" rel="nofollow noreferrer">a neutral hydrogen number density of $\sim0.1\text{ cm}^{-3}$</a>, which is a bit lower than the mean galactic neutral hydrogen number density. The Local Bubble itself is less dense than the LIC, <a href="http://www-ssg.sr.unh.edu/ism/LISM.html" rel="nofollow noreferrer">by about one or two orders of magnitude</a>. On the whole, this region of space is less dense than the ISM, on average.</p>

<p>So, if we take atomic hydrogen density to be a good benchmark, then the LIC and surrounding regions are in fact less dense than the Solar System on average.</p>

CC BY-SA 3.0
2017-10-27T19:27:19.257Z
2017-10-27T19:27:19.257Z
HDE 226868
<p>I once read that the solar wind is more or less blowing a "bubble" into the interstellar medium. However, the numbers I found while trying to verify this don't give me a clear picture yet:</p>

<ul>
<li>The <a href="https://en.wikipedia.org/wiki/Interplanetary_medium" rel="noreferrer">interplanetary medium</a> seems to have an average density of 5 particles per cm³ (at least near earth).</li>
<li>The <a href="https://en.wikipedia.org/wiki/Interstellar_medium" rel="noreferrer">interstellar medium</a> density varies widely, from 10⁻⁴ to 10⁶ particles per cm³.</li>
</ul>

<p>What I did not find was the density of the interstellar medium directly around the solar system. I know that the solar wind is interacting with the interstellar medium, which is responsible for the <a href="https://en.wikipedia.org/wiki/Heliosphere" rel="noreferrer">termination shock</a>, but I'm wondering if the density difference is large enough that one can say that the sun is actually blowing a "bubble" into the interstellar medium.</p>

<p>So, is the density inside the heliosphere much less than directly outside of it?</p>

<interstellar-medium><density><solar-wind>
Does the sun blow a bubble into the interstellar medium?
DarkDust
# Does the sun blow a bubble into the interstellar medium?

(Asked by: username_0 on 2017-10-27)

I once read that the solar wind is more or less blowing a "bubble" into the interstellar medium. However, the numbers I found while trying to verify this don't give me a clear picture yet:

* The [interplanetary medium](https://en.wikipedia.org/wiki/Interplanetary_medium) seems to have an average density of 5 particles per cm³ (at least near earth).
* The [interstellar medium](https://en.wikipedia.org/wiki/Interstellar_medium) density varies widely, from 10⁻⁴ to 10⁶ particles per cm³.

What I did not find was the density of the interstellar medium directly around the solar system. I know that the solar wind is interacting with the interstellar medium, which is responsible for the [termination shock](https://en.wikipedia.org/wiki/Heliosphere), but I'm wondering if the density difference is large enough that one can say that the sun is actually blowing a "bubble" into the interstellar medium.

So, is the density inside the heliosphere much less than directly outside of it?

**Tags:** interstellar-medium, density, solar-wind


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## 1 answers

### Answer by username_1 on 2017-10-27. Score: 4 | Accepted answer

At the moment, the Solar System is inside the [Local Interstellar Cloud](https://en.wikipedia.org/wiki/Local_Interstellar_Cloud) (which is itself within the [Local Bubble](https://en.wikipedia.org/wiki/Local_Bubble)). The LIC has [a neutral hydrogen number density of $\sim0.1\text{ cm}^{-3}$](http://iopscience.iop.org/article/10.1088/1742-6596/767/1/012016/pdf), which is a bit lower than the mean galactic neutral hydrogen number density. The Local Bubble itself is less dense than the LIC, [by about one or two orders of magnitude](http://www-ssg.sr.unh.edu/ism/LISM.html). On the whole, this region of space is less dense than the ISM, on average.

So, if we take atomic hydrogen density to be a good benchmark, then the LIC and surrounding regions are in fact less dense than the Solar System on average.


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