<p>There are two primary dust populations near 1 <a href="https://en.wikipedia.org/wiki/Astronomical_unit" rel="noreferrer">AU</a>, <a href="https://en.wikipedia.org/wiki/Interplanetary_medium" rel="noreferrer">interplanetary</a> dust (IPD) and <a href="https://en.wikipedia.org/wiki/Interstellar_medium" rel="noreferrer">interstellar</a> dust (ISD) [<em>Mann</em>, 2010].  I also discussed dust observations in detail at <a href="https://physics.stackexchange.com/a/160627/59023">https://physics.stackexchange.com/a/160627/59023</a>.</p>

<h1><strong>Interplanetary Dust</strong></h1>

<p>IPD of ~1 $\mu$m size drift sunward due to <a href="https://en.wikipedia.org/wiki/Poynting%E2%80%93Robertson_effect" rel="noreferrer">Poynting-Robertson drag</a> while following roughly Keplerian orbits [e.g., <em>Malaspina et al.</em>, 2014].  Closer to the sun, these particles break up due to collisions, <a href="https://en.wikipedia.org/wiki/Sublimation_(phase_transition)" rel="noreferrer">sublimation</a>/<a href="https://en.wikipedia.org/wiki/Ablation" rel="noreferrer">ablation</a>, and/or <a href="https://en.wikipedia.org/wiki/Sputtering" rel="noreferrer">sputtering</a>.</p>

<p>Dust grains of ~0.1 $\mu$m size are the so-called "$\beta$ meteorites", which travel away from the sun due to the imbalance of radiation pressure over gravity [<em>Mann</em>, 2010].</p>

<p>The smallest dust grains with $\ll$ 0.1 $\mu$m size, the so-called <em>nanograins</em> or <em>nanodust</em>, act like large <a href="https://en.wikipedia.org/wiki/Pickup_Ion" rel="noreferrer">pickup ions</a>, which are carried anti-sunward by the frame-dependent convective electric field (i.e., just the Lorentz force) produced when the dust grain moves relative to the <a href="http://en.wikipedia.org/wiki/Solar_wind" rel="noreferrer">solar wind</a> flow (i.e., $\mathbf{E}_{conv} = - \mathbf{V}_{sw} \times \mathbf{B}_{sw}$, where the subscript $conv$($sw$) stands for convective(solar wind), and $\mathbf{V}$ and $\mathbf{B}$ are the bulk flow velocity and quasi-static magnetic field).  These particles can reach speeds in excess of 100 km/s relative to the sun [<em>Meyer-Vernet et al.</em>, 2009].</p>

<h1><strong>Interstellar Dust</strong></h1>

<p>ISD was first discovered by the <a href="https://en.wikipedia.org/wiki/Ulysses_(spacecraft)" rel="noreferrer"><em>Ulysses</em></a> spacecraft, which is ~1 $\mu$m size and moves at ~26 km/s relative to the solar system barycenter.  More recent work [<em>Malaspina et al.</em>, 2014] has found a relationship between dust impact count rates and ecliptic longitude.</p>

<p>The reason can be seen from the following.  The Earth's transverse speed about the sun is ~29 km/s.  Thus, when the Earth moves anti-parallel(parallel) to the ISD flow direction the relative dust-spacecraft speed is ~55(~3) km/s, which produced an enhanced(depressed) dust count rate.  This occurs because there is a threshold impact speed necessary to produce a large enough <a href="https://en.wikipedia.org/wiki/Plasma_(physics)" rel="noreferrer">plasma</a> cloud (i.e., $\gtrsim$5-10 km/s depending on dust size) [<em>Meyer-Vernet et al.</em>, 2009; 2014].</p>

<blockquote>
  <p>What is the origin of the dust near the sun?</p>
</blockquote>

<p>The primary sources of ~1 $\mu$m size near 1 AU are cometary debris trails, asteroids, planets, moons, and ISD [<em>Mann</em>, 2010; <em>Zaslavsky</em>, 2015].  </p>

<blockquote>
  <p>Simply put - wouldn't the gravity pull it in or the solar wind blow it away?</p>
</blockquote>

<p>Some are attracted by a combination of gravity and Poynting-Robertson drag while the smaller grains are either "pushed" out by radiation pressure (i.e., $\beta$ meteorites) or "picked-up" by the solar wind Lorentz force (i.e., nanodust).</p>

<h1><strong>References</strong></h1>

<ul>
<li>D.M. Malaspina et al., "Interplanetary and interstellar dust observed by the Wind/WAVES electric field instrument," <em>Geophys. Res. Lett.</em> <strong>41</strong>, pp. 266-272, doi:10.1002/2013GL058786, 2014.</li>
<li>Mann, I. "Interstellar Dust in the Solar System," <em>Annual Review of Astronomy and Astrophysics</em> <strong>48</strong>, pp. 173-203, doi:10.1146/annurev-astro-081309-130846, 2010.</li>
<li>Meyer-Vernet, N., et al. "Dust detection by the Wave instrument on STEREO: Nanoparticles picked up by the solar wind?," <em>Sol. Phys.</em> <strong>256</strong>, pp. 463-474, doi:10.1007/s11207-009-9349-2, 2009.</li>
<li>Meyer-Vernet, N., et al. "The importance of monopole antennas for dust observations: Why Wind/WAVES does not detect nanodust," <em>Geophys. Res. Lett.</em> <strong>41</strong>, pp. 2716-2720, doi:10.1002/2014GL059988, 2014.</li>
<li>Zaslavsky, A. "Floating potential perturbations due to micrometeoroid impacts: Theory and application to S/WAVES data," <em>J. Geophys. Res.</em> <strong>120</strong>, pp. 855-867, doi:10.1002/2014JA020635, 2015.</li>
</ul>

CC BY-SA 3.0
2016-08-03T23:31:55.257Z
OK, this is extremely helpful - thanks for taking the time to put together a complete explanation with plenty of references. I'm really surprised how much is going on physically and also how much work has been dine!
uhoh
CC BY-SA 4.0
2022-05-06T21:00:14.933Z
So does the Poynting Robertson drag cause dust particles to fall into the sun?  Because your comment 'Closer to the sun, these particles break up due to collisions, sublimation/ablation, and/or sputtering'  makes it sound like they are broken down and carried away by the Solar wind/radiation.
Brooks Nelson
CC BY-SA 4.0
2022-05-06T21:40:11.057Z
@BrooksNelson - It depends on the size and density of the particles.  Some don't care and some do care a lot.  I don't recall off hand the nuances as I haven't dug into this in a while but I seem to recall ~1-10 micron-sized dust are affected by PR drag, ~0.1-1.0 micron are pushed out by radiation pressure, and those below are dominated by Lorentz force effects.  Inside of ~0.1 AU the ablation/sputtering effects start to matter (amount this matters depends on size of dust grain).
honeste_vivere
CC BY-SA 3.0
2016-08-03T19:33:15.867Z
2016-08-04T00:55:37.637Z
2017-04-13T12:40:15.377Z
honeste_vivere
<p><strong>note:</strong> Solar Probe+ is now officially <a href="https://en.wikipedia.org/wiki/Parker_Solar_Probe" rel="nofollow noreferrer">Parker Solar Probe</a></p>
<hr />
<p>In <a href="https://space.stackexchange.com/q/17498/12102">How can the Parker Solar Probe survive passing within 4 million miles of the sun's surface?</a> I asked about the <a href="http://solarprobe.jhuapl.edu/common/content/SolarProbePlusFactSheet.pdf" rel="nofollow noreferrer">Solar Probe Plus</a> mission. Reading a <a href="http://solarprobe.jhuapl.edu/mission/docs/SolarProbePlus2008.pdf" rel="nofollow noreferrer">2008 report</a> I saw that there is an elevated exposure to high velocity dust near the sun. I understand the high velocity, anything in orbit that close will be moving fast, but I don't understand why there is dust there.</p>
<p>Simply put - wouldn't the gravity pull it in or the solar wind blow it away?</p>
<p>What is the origin of the refractory carbon and silicates? Is this orbiting leftover material from the formation of the solar system, or is it falling in from farther out, or is it left-over carbon and silicon that fell into the early forming sun and is now being blown back out?</p>
<blockquote>
<p>4.3.5 Micrometeoroid and Dust. Solar Probe+ will encounter dust particles ranging in diameter from submicron up to several hundred microns and consisting of highly refractory carbon and silicate species with a typical bulk density of ~2.5 g/cm2. The particles will be traveling at relative speeds as high as 350 km/s. To define the shielding requirements for Solar Probe+, a dust model was developed based primarily on the work of Mann et al. (2004). The model employs the following assumptions...</p>
</blockquote>
<p><a href="https://i.sstatic.net/BtQ13.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/BtQ13.png" alt="Figure 4-6. Predicted dust environment at 0.1 AU (20 Rs) (from Mann et al. 2004 and Ishimoto, 2000)" /></a></p>
<p><strong>above:</strong> screen shot from <a href="http://solarprobe.jhuapl.edu/mission/docs/SolarProbePlus2008.pdf" rel="nofollow noreferrer">SolarProbePlus2008</a></p>
<p><a href="https://i.sstatic.net/ymUaM.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ymUaM.png" alt="Screen shot from NASA's Solar Probe Plus Fact Sheet" /></a></p>
<p><strong>above:</strong> screen shot from NASA's <a href="http://solarprobe.jhuapl.edu/common/content/SolarProbePlusFactSheet.pdf" rel="nofollow noreferrer">Solar Probe Plus Fact Sheet</a></p>
<p><a href="https://i.sstatic.net/aBM7A.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/aBM7A.jpg" alt="illustration of NASA's Solar Probe Plus from http://solarprobe.jhuapl.edu/spacecraft/" /></a></p>
<p><strong>above:</strong> illustration of NASA's Solar Probe Plus from <a href="http://solarprobe.jhuapl.edu/spacecraft/" rel="nofollow noreferrer">http://solarprobe.jhuapl.edu/spacecraft/</a> Sun is up - to state the obvious!</p>

CC BY-SA 3.0
2016-07-26T14:18:06.817Z
It's not light reading, but have you seen [this](http://adsabs.harvard.edu/full/1997A%26A...326..263K)?
called2voyage
CC BY-SA 3.0
2016-07-26T14:46:55.220Z
@called2voyage If you hit "print this article" you get a pdf. I searched for "source" and "origin" and didn't find those words. It definitely is an interesting discussion of the observations - during eclipses - as well as dust brought back to earth, but I don't see a "And the origin is...." definitive proclamation. But it's a good starting point for more reading - thanks!
uhoh
CC BY-SA 3.0
2016-07-26T15:18:41.663Z
One of the effects is probably [this...](https://en.wikipedia.org/wiki/Poynting%E2%80%93Robertson_effect) (kind of opposite of the yarkovsky effect. :)  )
Andy
CC BY-SA 3.0
2016-07-26T15:24:40.663Z
@Andy wow! Never heard of it, but it makes perfect sense - sort of a "dust magnet" and circularizer. So if this were basically what is happening, would the origin be part of the material that formed the solar system, raining down on the sun now because of the P-R effect? Sounds like an answer!
uhoh
CC BY-SA 3.0
2016-07-26T15:42:04.867Z
Well the P-R effect is one possible cause for an inspiral, but I guess comet activity and other things contribute a lot too. So I thought I'd leave it as a comment in case someone wants to check it out and maybe write it up. (I also tried to read [Mann's earlier paper](http://solarprobe.gsfc.nasa.gov/dust.pdf) but can't download it right now for some reason.)
Andy
CC BY-SA 3.0
2016-07-26T15:45:11.013Z
https://en.wikipedia.org/wiki/Interplanetary_dust_cloud They are not an equilibrium population, they must be continually produced.
ProfRob
CC BY-SA 3.0
2016-07-26T15:50:51.037Z
@RobJeffries I see, so there isn't really general agreement yet, but there are multiple possible sources and it sounds like it may turn out to be a mix?
uhoh
CC BY-SA 3.0
2016-07-29T09:02:21.843Z
I've asked a [related question here](http://space.stackexchange.com/q/17562/12102).
uhoh
CC BY-SA 3.0
2016-08-03T12:55:37.540Z
The P-R effect only works on dust grains in a certain mass/size range.  The smaller dust grains, called $\beta$ meteoroids (~0.1 $\mu$m in size), are actually "blown out" of the solar system by radiation pressure.  Most interplanetary dust of ~1 $\mu$m in size are remnants of cometary debris tails.  If the dust is small enough (i.e., sub nanometer sized) then they act like really heavy pickup ions and are accelerated by the solar wind's magnetic field.
honeste_vivere
CC BY-SA 3.0
2016-08-03T16:15:49.113Z
@honeste_vivere great - can you turn that into an answer? This turned out to be far more interesting than I expected!
uhoh
<the-sun><star-formation><planetary-formation><dust>
What is the origin of the dust near the sun?
uhoh
# What is the origin of the dust near the sun?

(Asked by: username_0 on 2016-07-26)

**note:** Solar Probe+ is now officially [Parker Solar Probe](https://en.wikipedia.org/wiki/Parker_Solar_Probe)

---

In [How can the Parker Solar Probe survive passing within 4 million miles of the sun's surface?](https://space.stackexchange.com/q/17498/12102) I asked about the [Solar Probe Plus](http://solarprobe.jhuapl.edu/common/content/SolarProbePlusFactSheet.pdf) mission. Reading a [2008 report](http://solarprobe.jhuapl.edu/mission/docs/SolarProbePlus2008.pdf) I saw that there is an elevated exposure to high velocity dust near the sun. I understand the high velocity, anything in orbit that close will be moving fast, but I don't understand why there is dust there.

Simply put - wouldn't the gravity pull it in or the solar wind blow it away?

What is the origin of the refractory carbon and silicates? Is this orbiting leftover material from the formation of the solar system, or is it falling in from farther out, or is it left-over carbon and silicon that fell into the early forming sun and is now being blown back out?

> 4.3.5 Micrometeoroid and Dust. Solar Probe+ will encounter dust particles ranging in diameter from submicron up to several hundred microns and consisting of highly refractory carbon and silicate species with a typical bulk density of ~2.5 g/cm2. The particles will be traveling at relative speeds as high as 350 km/s. To define the shielding requirements for Solar Probe+, a dust model was developed based primarily on the work of Mann et al. (2004). The model employs the following assumptions...

[![Figure 4-6. Predicted dust environment at 0.1 AU (20 Rs) (from Mann et al. 2004 and Ishimoto, 2000)](https://i.sstatic.net/BtQ13.png)](https://i.sstatic.net/BtQ13.png)

**above:** screen shot from [SolarProbePlus2008](http://solarprobe.jhuapl.edu/mission/docs/SolarProbePlus2008.pdf)

[![Screen shot from NASA's Solar Probe Plus Fact Sheet](https://i.sstatic.net/ymUaM.png)](https://i.sstatic.net/ymUaM.png)

**above:** screen shot from NASA's [Solar Probe Plus Fact Sheet](http://solarprobe.jhuapl.edu/common/content/SolarProbePlusFactSheet.pdf)

[![illustration of NASA's Solar Probe Plus from http://solarprobe.jhuapl.edu/spacecraft/](https://i.sstatic.net/aBM7A.jpg)](https://i.sstatic.net/aBM7A.jpg)

**above:** illustration of NASA's Solar Probe Plus from <http://solarprobe.jhuapl.edu/spacecraft/> Sun is up - to state the obvious!

**Tags:** the-sun, star-formation, planetary-formation, dust
> **Comments:**
> **username_1**: It's not light reading, but have you seen [this](http://adsabs.harvard.edu/full/1997A%26A...326..263K)?  
> **username_0**: @called2voyage If you hit "print this article" you get a pdf. I searched for "source" and "origin" and didn't find those words. It definitely is an interesting discussion of the observations - during eclipses - as well as dust brought back to earth, but I don't see a "And the origin is...." definitive proclamation. But it's a good starting point for more reading - thanks!  
> **username_2**: One of the effects is probably [this...](https://en.wikipedia.org/wiki/Poynting%E2%80%93Robertson_effect) (kind of opposite of the yarkovsky effect. :)  )  
> **username_0**: @Andy wow! Never heard of it, but it makes perfect sense - sort of a "dust magnet" and circularizer. So if this were basically what is happening, would the origin be part of the material that formed the solar system, raining down on the sun now because of the P-R effect? Sounds like an answer!  
> **username_2**: Well the P-R effect is one possible cause for an inspiral, but I guess comet activity and other things contribute a lot too. So I thought I'd leave it as a comment in case someone wants to check it out and maybe write it up. (I also tried to read [Mann's earlier paper](http://solarprobe.gsfc.nasa.gov/dust.pdf) but can't download it right now for some reason.)  
> **username_3**: https://en.wikipedia.org/wiki/Interplanetary_dust_cloud They are not an equilibrium population, they must be continually produced.  
> **username_0**: @RobJeffries I see, so there isn't really general agreement yet, but there are multiple possible sources and it sounds like it may turn out to be a mix?  
> **username_0**: I've asked a [related question here](http://space.stackexchange.com/q/17562/12102).  
> **username_4**: The P-R effect only works on dust grains in a certain mass/size range.  The smaller dust grains, called $\beta$ meteoroids (~0.1 $\mu$m in size), are actually "blown out" of the solar system by radiation pressure.  Most interplanetary dust of ~1 $\mu$m in size are remnants of cometary debris tails.  If the dust is small enough (i.e., sub nanometer sized) then they act like really heavy pickup ions and are accelerated by the solar wind's magnetic field.  
> **username_0**: @honeste_vivere great - can you turn that into an answer? This turned out to be far more interesting than I expected!  

---

## 1 answers

### Answer by username_4 on 2016-08-03. Score: 8 | Accepted answer

There are two primary dust populations near 1 [AU](https://en.wikipedia.org/wiki/Astronomical_unit), [interplanetary](https://en.wikipedia.org/wiki/Interplanetary_medium) dust (IPD) and [interstellar](https://en.wikipedia.org/wiki/Interstellar_medium) dust (ISD) [*Mann*, 2010]. I also discussed dust observations in detail at <https://physics.stackexchange.com/a/160627/59023>.

# **Interplanetary Dust**

IPD of ~1 $\mu$m size drift sunward due to [Poynting-Robertson drag](https://en.wikipedia.org/wiki/Poynting%E2%80%93Robertson_effect) while following roughly Keplerian orbits [e.g., *Malaspina et al.*, 2014]. Closer to the sun, these particles break up due to collisions, [sublimation](https://en.wikipedia.org/wiki/Sublimation_(phase_transition))/[ablation](https://en.wikipedia.org/wiki/Ablation), and/or [sputtering](https://en.wikipedia.org/wiki/Sputtering).

Dust grains of ~0.1 $\mu$m size are the so-called "$\beta$ meteorites", which travel away from the sun due to the imbalance of radiation pressure over gravity [*Mann*, 2010].

The smallest dust grains with $\ll$ 0.1 $\mu$m size, the so-called *nanograins* or *nanodust*, act like large [pickup ions](https://en.wikipedia.org/wiki/Pickup_Ion), which are carried anti-sunward by the frame-dependent convective electric field (i.e., just the Lorentz force) produced when the dust grain moves relative to the [solar wind](http://en.wikipedia.org/wiki/Solar_wind) flow (i.e., $\mathbf{E}\_{conv} = - \mathbf{V}\_{sw} \times \mathbf{B}\_{sw}$, where the subscript $conv$($sw$) stands for convective(solar wind), and $\mathbf{V}$ and $\mathbf{B}$ are the bulk flow velocity and quasi-static magnetic field). These particles can reach speeds in excess of 100 km/s relative to the sun [*Meyer-Vernet et al.*, 2009].

# **Interstellar Dust**

ISD was first discovered by the [*Ulysses*](https://en.wikipedia.org/wiki/Ulysses_(spacecraft)) spacecraft, which is ~1 $\mu$m size and moves at ~26 km/s relative to the solar system barycenter. More recent work [*Malaspina et al.*, 2014] has found a relationship between dust impact count rates and ecliptic longitude.

The reason can be seen from the following. The Earth's transverse speed about the sun is ~29 km/s. Thus, when the Earth moves anti-parallel(parallel) to the ISD flow direction the relative dust-spacecraft speed is ~55(~3) km/s, which produced an enhanced(depressed) dust count rate. This occurs because there is a threshold impact speed necessary to produce a large enough [plasma](https://en.wikipedia.org/wiki/Plasma_(physics)) cloud (i.e., $\gtrsim$5-10 km/s depending on dust size) [*Meyer-Vernet et al.*, 2009; 2014].

> What is the origin of the dust near the sun?

The primary sources of ~1 $\mu$m size near 1 AU are cometary debris trails, asteroids, planets, moons, and ISD [*Mann*, 2010; *Zaslavsky*, 2015].

> Simply put - wouldn't the gravity pull it in or the solar wind blow it away?

Some are attracted by a combination of gravity and Poynting-Robertson drag while the smaller grains are either "pushed" out by radiation pressure (i.e., $\beta$ meteorites) or "picked-up" by the solar wind Lorentz force (i.e., nanodust).

# **References**

* D.M. Malaspina et al., "Interplanetary and interstellar dust observed by the Wind/WAVES electric field instrument," *Geophys. Res. Lett.* **41**, pp. 266-272, doi:10.1002/2013GL058786, 2014.
* Mann, I. "Interstellar Dust in the Solar System," *Annual Review of Astronomy and Astrophysics* **48**, pp. 173-203, doi:10.1146/annurev-astro-081309-130846, 2010.
* Meyer-Vernet, N., et al. "Dust detection by the Wave instrument on STEREO: Nanoparticles picked up by the solar wind?," *Sol. Phys.* **256**, pp. 463-474, doi:10.1007/s11207-009-9349-2, 2009.
* Meyer-Vernet, N., et al. "The importance of monopole antennas for dust observations: Why Wind/WAVES does not detect nanodust," *Geophys. Res. Lett.* **41**, pp. 2716-2720, doi:10.1002/2014GL059988, 2014.
* Zaslavsky, A. "Floating potential perturbations due to micrometeoroid impacts: Theory and application to S/WAVES data," *J. Geophys. Res.* **120**, pp. 855-867, doi:10.1002/2014JA020635, 2015.

> **Comments:**
> **username_0**: OK, this is extremely helpful - thanks for taking the time to put together a complete explanation with plenty of references. I'm really surprised how much is going on physically and also how much work has been dine!  
> **username_5**: So does the Poynting Robertson drag cause dust particles to fall into the sun?  Because your comment 'Closer to the sun, these particles break up due to collisions, sublimation/ablation, and/or sputtering'  makes it sound like they are broken down and carried away by the Solar wind/radiation.  
> **username_4**: @BrooksNelson - It depends on the size and density of the particles.  Some don't care and some do care a lot.  I don't recall off hand the nuances as I haven't dug into this in a while but I seem to recall ~1-10 micron-sized dust are affected by PR drag, ~0.1-1.0 micron are pushed out by radiation pressure, and those below are dominated by Lorentz force effects.  Inside of ~0.1 AU the ablation/sputtering effects start to matter (amount this matters depends on size of dust grain).  

---

