<p>Comets have three tails:</p>
<ul>
<li>A dust tail, that comprises very small neutral particles of dust. The dust tail is carried away from the comet by solar radiation pressure.</li>
<li>An ion tail, that comprises very small ionized particles. These are affected by the solar wind as well as radiation pressure.</li>
<li>An anti-tail, that comprises not so small particles ejected from the comet, too large for radiation pressure to play a significant role (which means tens of micrometers in diameter, or more). The anti-tail can be very hard to see, and some comets don't have them.</li>
</ul>
<p>It is the anti-tail that provides the materials for those periodic meteor showers. The very small particles in the dust tail and ion tail are swept away from the solar system by radiation pressure and the solar wind in rather short order. The particles in the anti-tail remain close to the comet's orbital path, but spread out along the orbit, for multiple orbits.</p>

CC BY-SA 4.0
2024-10-31T11:12:56.143Z
2024-10-31T11:12:56.143Z
David Hammen
<p>It's orbital mechanics. If a comet ejects a rock with a very small velocity, the rock winds up in an orbit very similar to the comet. However, that orbit may have a <em>slightly</em> different period. So, over many orbits, the rock drifts along the orbit with little sideways displacement. Changes in the other orbital elements don't cause a displacement that accumulates with time like the displacement caused by a change in orbital period.</p>

<p>Oddly, if the comet ejects the rock forward, the rock's orbital period increases, so it soon falls behind the comet, and continues to do so on the average as time goes on.</p>

CC BY-SA 4.0
2020-04-24T23:46:30.103Z
yep yep, concise and nice. Thanks!
uhoh
CC BY-SA 4.0
2020-04-24T21:13:40.540Z
2020-04-24T21:13:40.540Z
John Doty
<p>The cometary particles need not retain the exact same orbit as the comet in order to stay close together near perihelion, thus where their orbit passes Earth's orbit.</p>

<p>Slight changes in the orbital parameters of the released dust particles can include slighly higher or lower aphelion, and thus change the revolution time and the time of perihelion (Earth) passage enough to spread out the particles. Over many revolutions it will eventually spread out over the whole orbit.</p>

<p>Additionally the orbits by the dust particles are subject to changes due to interaction with the solar wind and solar radiation which will over time change their orbits (yorp effect, Yarkovsky effect, radiation pressure etc).</p>

<p>This behaviour also explains that the meteor showers will be stronger in some years when Earth passes through a part where particles have not yet had time to more equally disperse.</p>

<p>Addendum: The other question on tails <a href="https://astronomy.stackexchange.com/questions/35914/how-can-comets-have-tails-if-theres-no-air-resistance-in-space">How can comets have tails if there&#39;s no air resistance in space?</a> is related. Yet the (visible) tails are caused by either (ionized) gas or (small) dust particles (nm ... µm) which scatter the light. While these dust particles certainly also can make meteors, the larger the particles are, the less efficiently radiation pressure works on them, so their orbital evolution is much slower. And comets do release also a lot of bigger particles from µm up to cm (excact size distriubtion subject to disussion and analysis especially as follow-up to Rosetta mission, also depending on comet size and age) which are not easily visible in the visible light when observing it from Earth.</p>

CC BY-SA 4.0
2020-04-24T20:01:32.413Z
I think we screwed up way back then by calling them "tails", since they don't necessarily lag *behind* the comet in its orbit, but are pulled away from it by gravitational forces.
Darrel Hoffman
CC BY-SA 4.0
2020-04-24T20:51:44.460Z
Gravity has nothing to do with the tails; see the linked other thread in my answer
planetmaker
CC BY-SA 4.0
2020-04-24T21:16:46.090Z
Oops, sorry, not gravity, magnetic field.  Anyhow, the direction of the tail definitely does not indicate the direction of movement.
Darrel Hoffman
CC BY-SA 4.0
2020-04-24T07:43:01.410Z
2020-04-24T11:38:50.823Z
2020-04-24T11:38:50.823Z
planetmaker
<p>My understanding of the meteor showers that repeat yearly is that the Earth passes through the orbit of a comet that is nowhere near us, and might not even exist anymore, yet it's orbit is filled with a stream of dust in the same heliocentric orbit by <em>way ahead of</em> or behind their cometary source by tens of millions of kilometers or more.</p>

<p>How do these particles spread out along the comet's orbit so far and yet remain tightly correlated transverse to the orbit? Some meteor showers like the "Unicorn shower" linked below can be quite short, lasting only a fraction of a day!</p>

<ul>
<li><a href="https://astronomy.stackexchange.com/q/34018/7982">What makes some meteor showers continue for days, while the &quot;Unicorn shower&quot; can be shorter than one hour?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/23555/7982">Meteor shower predicted to be best viewed BEFORE midnight (for reasons other than the moon)?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/20597/7982">Why are these objects moving at Vastly Different Speeds along the same orbit?</a></li>
</ul>

<p><strong>Left:</strong> From <a href="https://astronomy.stackexchange.com/q/17853/7982">What (actually) is Jupiter doing to this year&#39;s Perseids meteor shower?</a> <strong>Right:</strong> From <a href="https://astronomy.stackexchange.com/q/27301/7982">Why would the Perseids meteor rate fall off after maximum faster than the increase before maximum?</a> - click each for full size</p>

<p><a href="https://i.sstatic.net/PevJe.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/PevJem.jpg" alt="enter image description here"></a> <a href="https://i.sstatic.net/15EvV.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/15EvVm.jpg" alt="enter image description here"></a></p>

<solar-system><orbital-mechanics><comets><meteor-shower>
Why do particles from a comet that result in meteor showers spread out mostly along the comet's orbit?
uhoh
# Why do particles from a comet that result in meteor showers spread out mostly along the comet's orbit?

(Asked by: username_0 on 2020-04-24)

My understanding of the meteor showers that repeat yearly is that the Earth passes through the orbit of a comet that is nowhere near us, and might not even exist anymore, yet it's orbit is filled with a stream of dust in the same heliocentric orbit by *way ahead of* or behind their cometary source by tens of millions of kilometers or more.

How do these particles spread out along the comet's orbit so far and yet remain tightly correlated transverse to the orbit? Some meteor showers like the "Unicorn shower" linked below can be quite short, lasting only a fraction of a day!

* [What makes some meteor showers continue for days, while the "Unicorn shower" can be shorter than one hour?](https://astronomy.stackexchange.com/q/34018/7982)
* [Meteor shower predicted to be best viewed BEFORE midnight (for reasons other than the moon)?](https://astronomy.stackexchange.com/q/23555/7982)
* [Why are these objects moving at Vastly Different Speeds along the same orbit?](https://astronomy.stackexchange.com/q/20597/7982)

**Left:** From [What (actually) is Jupiter doing to this year's Perseids meteor shower?](https://astronomy.stackexchange.com/q/17853/7982) **Right:** From [Why would the Perseids meteor rate fall off after maximum faster than the increase before maximum?](https://astronomy.stackexchange.com/q/27301/7982) - click each for full size

[![enter image description here](https://i.sstatic.net/PevJem.jpg)](https://i.sstatic.net/PevJe.jpg) [![enter image description here](https://i.sstatic.net/15EvVm.jpg)](https://i.sstatic.net/15EvV.jpg)

**Tags:** solar-system, orbital-mechanics, comets, meteor-shower

---

## 3 answers

### Answer by username_3 on 2020-04-24. Score: 7 | Accepted answer

The cometary particles need not retain the exact same orbit as the comet in order to stay close together near perihelion, thus where their orbit passes Earth's orbit.

Slight changes in the orbital parameters of the released dust particles can include slighly higher or lower aphelion, and thus change the revolution time and the time of perihelion (Earth) passage enough to spread out the particles. Over many revolutions it will eventually spread out over the whole orbit.

Additionally the orbits by the dust particles are subject to changes due to interaction with the solar wind and solar radiation which will over time change their orbits (yorp effect, Yarkovsky effect, radiation pressure etc).

This behaviour also explains that the meteor showers will be stronger in some years when Earth passes through a part where particles have not yet had time to more equally disperse.

Addendum: The other question on tails [How can comets have tails if there's no air resistance in space?](https://astronomy.stackexchange.com/questions/35914/how-can-comets-have-tails-if-theres-no-air-resistance-in-space) is related. Yet the (visible) tails are caused by either (ionized) gas or (small) dust particles (nm ... µm) which scatter the light. While these dust particles certainly also can make meteors, the larger the particles are, the less efficiently radiation pressure works on them, so their orbital evolution is much slower. And comets do release also a lot of bigger particles from µm up to cm (excact size distriubtion subject to disussion and analysis especially as follow-up to Rosetta mission, also depending on comet size and age) which are not easily visible in the visible light when observing it from Earth.

> **Comments:**
> **username_4**: I think we screwed up way back then by calling them "tails", since they don't necessarily lag *behind* the comet in its orbit, but are pulled away from it by gravitational forces.  
> **username_3**: Gravity has nothing to do with the tails; see the linked other thread in my answer  
> **username_4**: Oops, sorry, not gravity, magnetic field.  Anyhow, the direction of the tail definitely does not indicate the direction of movement.  

---

### Answer by username_1 on 2024-10-31. Score: 4

Comets have three tails:

* A dust tail, that comprises very small neutral particles of dust. The dust tail is carried away from the comet by solar radiation pressure.
* An ion tail, that comprises very small ionized particles. These are affected by the solar wind as well as radiation pressure.
* An anti-tail, that comprises not so small particles ejected from the comet, too large for radiation pressure to play a significant role (which means tens of micrometers in diameter, or more). The anti-tail can be very hard to see, and some comets don't have them.

It is the anti-tail that provides the materials for those periodic meteor showers. The very small particles in the dust tail and ion tail are swept away from the solar system by radiation pressure and the solar wind in rather short order. The particles in the anti-tail remain close to the comet's orbital path, but spread out along the orbit, for multiple orbits.


---

### Answer by username_2 on 2020-04-24. Score: 2

It's orbital mechanics. If a comet ejects a rock with a very small velocity, the rock winds up in an orbit very similar to the comet. However, that orbit may have a *slightly* different period. So, over many orbits, the rock drifts along the orbit with little sideways displacement. Changes in the other orbital elements don't cause a displacement that accumulates with time like the displacement caused by a change in orbital period.

Oddly, if the comet ejects the rock forward, the rock's orbital period increases, so it soon falls behind the comet, and continues to do so on the average as time goes on.

> **Comments:**
> **username_0**: yep yep, concise and nice. Thanks!  

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