Stargazing Spotting Meteorites: Unveiling the Mystery of Annual Showers

[sophiecentaur]

There are probably none with the near circular orbit that the Earth or other planets have

This may be true (or nearly true) but there are a lot of objects with orbits that intersect Earth's orbit +/- little enough to worry us sometimes. (I'm still trying to tie in the trail of a comet with what happens to the resulting bits from a blown-up asteroid) The products of an exploded asteroid will have a range of orbits spread around the CM of the original asteroid. At some point in the future (next or tenth time round - depending) when the orbits of those bits of rock again rendezvous with the Earth, there is a greater chance of a collision with one of them, So they need to be broken up into relatively harmless sized bits, with a consequently greater chance of actually hitting us.
The alternative of guiding an asteroid out of harm's way is more attractive - but only if the rocket power exists. From what I understand of orbital mechanics, shifting an object into a significantly different orbit would involve more than just one impulse. So the rocket would need to sit on the asteroid and give it another nudge at a suitable time.

 

[DaveC426913]

From what I understand of orbital mechanics, shifting an object into a significantly different orbit would involve more than just one impulse.

Not necessarily. A single impulse would change the eccentricity of its orbit, though one of its *apses (either apsis or periapsis) will remain the same.

This surely reduces the overall collision risk by many orders of magnitude - which is probably sufficient.

Consider also that it may be effective to simply change the inclination of a menacing asteroid's orbit. Little energy required for maximum reduction in collision risk.

 

[davenn]

Wait. Earth - and the other planets - have their own co-orbiting objects, including - but not limited to -Trojans.

Those are NOT comet trails which is what is being spoken of ... ... dust trails left my comets and the resulting meteor showers

 

[davenn]

This may be true (or nearly true) but there are a lot of objects with orbits that intersect Earth's orbit +/- little enough to worry us sometimes.

Yes, there's lots of meteoroids and asteroids with orbits that cross Earths orbit, but as I just replied to DaveC ... you are asking about comet dust trails and their paths are all highly elliptical

 

[davenn]

The co-orbital asteroids are also good candidates, very low eccentricity in some of them like 2002 AA29 and 2003 YN107.

Again ... those are asteroids you speak of, not cometary dust trails that the thread is about

 

[davenn]

It's not the only one, there is another trojan (2020 XL5 - significantly more eccentric though) discovered recent and if you go to the JPL Small-Body Database Search Engine you can find (say searching for NEOs AND a = [ 0.98, : 1.02 ] (au) AND e < 0.2 ) a bunch of (non-trojan) asteroids in similar orbits to Earth like 469219 Kamo'oalewa.

You are naming asteroids not comets

 

[sophiecentaur]

you are asking about comet dust trails and their paths are all highly elliptical

I realize that I have shifted the thread a bit but, as OP, I feel I have some editorial rights and there are clear parallels between all objects which go near Earth at some stage. It must be a matter of the difference between extremes. The eccentricity of an orbit will affect details but which details are relevant?
I now understand about how particles ejected from a comet with equal speeds in all directions will be spread out along the path (at 1AU) much more than across it and that was useful for me. For an asteroid with a less elliptical orbit, this difference will be less so there will be much less of a 'trail' if it explodes and the result will be more of a 'cloud' than a trail. So that could imply that we would need to coincide in time as well as in position with asteroid pieces, whereas bits of the comet trail are always present when we get to that particular position in our orbit.
I think that has been a useful clearing up lesson - for me if for no one else. I like it when things tie together.

 

[DaveC426913]

Those are NOT comet trails which is what is being spoken of ... ... dust trails left my comets and the resulting meteor showers

Yes. But you/we keep expanding the scope of the thread.

I mean, I know we're touching on a number of related subjects, but I think the parameters of the original thesis may have gotten clouded.

 

[snorkack]

I realize that I have shifted the thread a bit but, as OP, I feel I have some editorial rights and there are clear parallels between all objects which go near Earth at some stage. It must be a matter of the difference between extremes. The eccentricity of an orbit will affect details but which details are relevant?
I now understand about how particles ejected from a comet with equal speeds in all directions will be spread out along the path (at 1AU) much more than across it and that was useful for me. For an asteroid with a less elliptical orbit, this difference will be less so there will be much less of a 'trail' if it explodes and the result will be more of a 'cloud' than a trail. So that could imply that we would need to coincide in time as well as in position with asteroid pieces, whereas bits of the comet trail are always present when we get to that particular position in our orbit.

No.
It starts as a cloud - but quickly turns into trail along orbit.
Why?
Imagine that a number of particles are ejected from, for example, Earth, in all directions with equal speed.
Say that ejection happens when Earth is at perihelion, 147 million km from Sun, and a particle ejected backwards goes to an elliptical orbit for which 147 million km is aphelion, with perihelion at 142 million km.
In half a year, the Earth is at its aphelion at 152 million km, and the ejected particle is at its new perihelion at 142 million km... 10 million km from Earth orbit.
This is the furthest it ever gets from Earth orbit, and Earth´s meteor trail. For it follows its new closed orbit, and over the next half year returns to its original point of impact, as it always must.
It returns to its original point of impact... but does not need to fall back to Earth. Because while its new orbit intersects Earth orbit, it has a different (though close) period. With long half-axis of ellipse 5 million km shorter than Earth it has orbital period 18 days shorter. So it passes the exact point of collision on Earth orbit... but Earth is then not there, but 50 million km behind.
Over a number of orbital periods, the displacement along orbit accumulates freely. Displacement across orbit faces a returning force and is maximized in the first half orbital period.

 

[sophiecentaur]

It starts as a cloud - but quickly turns into trail along orbit.
Why?

I am not in favour of using the Earth as a model because any particles ejected from Earth will not have escape velocity. I would think the better to stick with the comet explanation in terms of a comet.
A comet trail won't start as a cloud. It will be formed over a long part of the comet's path as it approaches the Sun and bits boil off.
Then apply simple orbital mechanics (and ignore the attraction to the comet itself) the behaviour of an object in orbit (just one of the particles that are ejected by the comet as it heats up). A single impulse will cause its orbit to change but it will always revisit the point at which it was ejected. This will mean that the trail will be constrained to its original path (plus or minus a bit) and every bit will arrive back on the comet's orbit but at a different time. The speed of the comet is far greater than the speed of the ejecta and the escape velocity from such a lightweight as a comet can easily be exceeded by some of the ejecta so we need only be concerned with the orbits of the particles around the Sun.

 

[neilparker62]

@davenn looks for them in his mailbox.

So who's mail order was this ?

 

[Oldman too]

If you like https://earthobservatory.nasa.gov/images/149554/finding-meteorite-hotspots-in-antarctica

You will love https://www.science.org/doi/10.1126/sciadv.abj8138

 

[Keith_McClary]

A comet trail won't start as a cloud. It will be formed over a long part of the comet's path as it approaches the Sun and bits boil off.

 

[sophiecentaur]

I wonder about that video. I have always understood that the tail points away from the Sun all the way round. I expect an Artist may have intervened at some stage(?).

 

[DaveC426913]

I wonder about that video. I have always understood that the tail points away from the Sun all the way round. I expect an Artist may have intervened at some stage(?).

Many comets have two tails. Only one points away from Sun.

 

[Keith_McClary]

I wonder about that video. I have always understood that the tail points away from the Sun all the way round. I expect an Artist may have intervened at some stage(?).

These are the particles so large that they are more influenced by gravity than light.

Cometary dust trails are the collections of large (greater than 0.1 mm) particles that closely follow a comet's orbit, similar to how a contrail follows a jet. Dust trails are the youngest meteoroid streams, and when they intersect the orbit of a planet they can create meteor showers.

 

[sophiecentaur]

Many comets have two tails. Only one points away from Sun.
View attachment 298315

I know about dust trails but are they ever on the Sun-side of the orbit? What mechanism woul cause their trajectory to take the particles towards the Sun?
Particles that have not totally escaped the core will return and cross the main track eventually (at some time). Would that intersection take significant numbers back in enough numbers to be visible?

 

[sophiecentaur]

These are the particles so large that they are more influenced by gravity than light.

Dust trails: is there some orbital thing which causes the ejected particles to re-appear on the comet's orbital path only to one side. I already made the point that slow particles will hang around the comet's path but the form of the dust trail seems to suggest strongly that the Sun(?) is having an effect. Also, there is a distinction between the two tails where I would (naively?) have thought it would cause a widened single tail.
Edit; the distinction seems to be due to ionisation in one case and the solar wind in the other - both causes being of solar origin so you'd expect displacement away from the Suns general direction (modified by magnetic fields).

 

[davenn]

Many comets have two tails. Only one points away from Sun.

both those are pointing away from the sun

but there is one style that does point in the opposite direction tail
An anti-tail

Wiki
""Most comets do not develop sufficiently for an antitail to become visible, but notable comets that did display antitails include Comet Arend–Roland in 1957, Comet Hale–Bopp in 1997, and Comet PANSTARRS in 2013. The coma and tail at the main Comet article.""

Arend-Roland comet - C/1956 R1

 

[Keith_McClary]

re-appear on the comet's orbital path only to one side.

I think their motion is due to the ejection speed from the comet. Most of the ejection is from the hot (sunny) side.

 

[sophiecentaur]

I think their motion is due to the ejection speed from the comet. Most of the ejection is from the hot (sunny) side.

I was wondering about that and it does make sense, qualitatively. Orbital shape and period would affect the surface temperature due to exposure times to high solar radiation. The JWST, which always points one side at the Sun and on which the solar shield maintains more than 300K difference between near and far sides. That sort of difference could well account for local, selective boiling-off of some materials, depending on the exposure time and perigee. Perhaps short period comets would do this differently from longer period comets.

Nothing is ever simple in space!