Main belt comets

[sol88]

What are peoples thoughts on why main belt comets go "active" while thier close compnions DO not?

My thinking is they pass thru an area of differnet space weather, so as they become active until such time as they leave that area.

In particular http://www.planetary.org/blog/article/00000551/

Eccentricity can not be the only factor.

[helal]

My thinking is they pass thru an area of differnet space weather, so as they become active until such time as they leave that area.

[mharratsc]

Perhaps eccentricity is the trigger for the cometary discharge, but I'm sure it's not the cause.

If I understand them correctly, they're somewhat larger asteroids with a slighty eccentric orbit. They tend to flare towards perihelion.

I would think that these bodies tend to charge and discharge a bit differently than planets, moons, and other 'traditional' comets. They have a negative charge with regards to the Sun. They may accumulate more of a negative charge due to interaction with each other, or the magnetotail of Mars, or possibly some interaction with Jupiter.

Once this negative charge built up ever so slightly, it's orbital eccentricity might cause it to equalize it's charge at closest approach to the Sun in a cometary fashion. I would think since these asteroids do not travel quite so far away from the Sun as do actual 'comets' that they would therefore have much more passive displays when they do equalize their charges, since they're never building up such a differential of charge in the first place. Thus, they will nudge a little closer to the Sun, flare a bit, then get pulled back away from the Sun to start developing a slighty more negative charge all over again, waiting for next perihelion.

You know- I just had a thought. I've never heard this mentioned before, but- if comets (of any type really) approach the Sun and start blowing off matter by plasma reduction... wouldn't they then on their return to the outer reaches of the solar environment also accrete more matter by plasma deposition??

Maybe that's why comets last so long? They shoot towards the Sun and lose a few meters of their surface material, and then head back out to the outer fringes to pick up a few meters- lather, rinse, and repeat!

Just a thought. Anyway, sorry to wander off like that. I'm not a scientist, but from what I've learned about the properties of charge equalization in space plasmas that is my best guess.

Mike H.

[solrey]

Here's a link to the abstract by Hsieh:
http://arxiv.org/abs/0907.5505

And the full paper in PDF:
http://arxiv.org/pdf/0907.5505v1

Nowhere do they mention a spectral analysis of any sort, so to say that these asteroids cometary outbursts are due to water ice sublimation, mentioned 11 times in the paper, is nothing more than circular reasoning around an erroneous theory on the nature of comets being dirty ice balls in the first place.

Too many other theories, such as the origin of water on Earth, rely on the dirty snowball theory, that mainstream science is not going to let go of their muddy icecubes any time soon, regardless of the continuous and mounting evidence that says asteroids and comets are essentially the same, the only significant difference being that comets are asteroids in a state of charge imbalance relative to the solar plasma stream, with the accompanying surface sputtering and coma/plasma DL.

Technically, comet should be a verb, not a noun.

[redeye]

Eccentricity can not be the only factor.

The composition of the comet may be a factor as well it's size and speed. The composition and size can affect the amount of "charge" the object has and it's speed and eccentricity could affect how quickly a charge imbalance builds up. I wonder if this may have any implications for the New Horizons probe?

Cheers!

[redeye]

If the ion tail loading is sufficient, then the magnetic field lines are squeezed together to the point where, at some distance along the ion tail, magnetic reconnection occurs. This leads to a "tail disconnection event".[20] This has been observed on a number of occasions, notable among which was on the 20th. April 2007 when the ion tail of comet Encke was completely severed as the comet passed through a coronal mass ejection. This event was observed by the STEREO spacecraft.[21]

From wiki

Magnetic reconnection...it can do anything!

Cheers!

[mharratsc]

ROFl!!


Mike H.

[Noli Me Tangere]

Perhaps eccentricity is the trigger for the cometary discharge, but I'm sure it's not the cause.

I have a hypothesis for the trigger of the beginning of the cometary discharge (the appearance of the coma). Firs I want to recap the modes of the flow of the currents in plasma, according to Don Scott http://www.electric-cosmos.org/electricplasma.htm:

1. Dark Current Mode - The strength of the electrical current (flow of charged particles) within the plasma is very low. The plasma does not glow. It is essentially invisible. We would not know a plasma was there at all unless we measured its electrical activity with sensitive instruments. The present day magnetospheres of the planets are examples of plasmas operating in the dark current mode.
2. Normal Glow Mode - The strength of the electrical current (flow of charged particles) is significant. The entire plasma glows. The brightness of the glow depends on the intensity of the current in the plasma. Examples: Any neon sign. Emission nebulae. The Sun's corona.
3. Arc Mode - The strength of the electrical current in the plasma is very high. The plasma radiates brilliantly over a wide spectrum. Current tends to form twisting filaments. Examples of this mode of operation are: An electric arc welding machine. Lightning. The Sun's photosphere.

Now, the beginning of the cometary discharge seems to me like the transition between the dark current mode and the normal glow mode. Remember, a neon sign is a plasma in normal glow mode. What is needed for a neon sign to start glowing? Exactly, a [url2=http://en.wikipedia.org/wiki/Fluorescent_lamp]glow starter[/url2].
In space it could happen like this:
The comet enters the solar system; it begins to accumulate charge. Its double layer is still in the dark current mode. Suddenly, the comet enters a region with a greater current density (maybe one of the branches of the Birkeland currents that permeate the solar system). This acts like a glow starter.
Once the comet lits, the current density can decrease (e.g. the comet exists the above mentioned branch of the Birkeland currents) and the comet continues to glow, similar to the neon sign.
Of course, in average, the current density increases as the comet aproaches the sun; that's why the coma increases.
The comet exits the glow mode when the current density decreases under the threshold needed for sustaining the glow mode (as it exits the solar system).

I'll be glad to hear your thoughts on it.

[sol88]

Sounds reasonable to me, would explain MBC's unexpected flares. They pass through a Birkeland current. They can turn "on" and "off".

[solrey]

I believe the asteroid with the most eccentricity is also the only one that comets with regularity, which happens during perihelion. Go figger.

Considering what might cause a few low eccentricity asteroids to comet at random, while nearby asteroids do not, the off-gassing of an inner planet being carried along with the solar plasma stream came to mind. I think there is a possibility of a narrow stream of inner planet off-gassing to initiate an electro-chemical reaction, being the trigger of a cometary glow discharge by providing free particles that cascade into an "electron storm", without requiring an increase in electro-static, or voltage, potential.
I wonder what the positions of the inner planets were in relation to the MBC's during their comet phase.

Of course, interacting with a more energetic plasma filament/Birkeland current would do the trick too.

My thoughts are that both EDM and electro-chemical reactions occur on comets in a positive feedback mechanism.

[Noli Me Tangere]

Sounds reasonable to me, would explain MBC's unexpected flares. They pass through a Birkeland current. They can turn "on" and "off".

To my knowledge, once the discharge is activated the current must weaken under a certain value for the discharge to cease. That would explain why the comet, once lit, remains lit and only turns off when departing.

[solrey]

Little tidbits of corroborating evidence are sometimes found in the oddest of places.

The following was in a paper linked in this article about a spaceprobe thruster, the EMdrive. That came from this forum post. h/t to earls.

Professor Yang Juan stops just short of explicitly recommending plasma attacks for China, yet her
enthusiasm for demonstrating the feasibility of this approach seems obvious.
“This paper studies the effectiveness of using plasma to interrupt low-orbit reconnaissance satellite
operations and proposes a scheme for using plasma against satellites. Analysis of satellite charging and
discharging effects and mechanisms in a plasma environment indicates that plasma damages low-orbit
satellites by causing arc-discharging potential differences to form on the surface of a satellite and that
produces strong arc currents and electromagnetic pulses that damage solar cells, surface temperature
control materials, microwave and electronic instruments on a satellite, and disrupts normal antenna
operations. This study divided a satellite surface into 14 different equivalent parts, and using equivalent
charging modes, calculated the charging processes of high-density low-energy and medium-energy
plasmas on the satellite surfaces, analyzed the effects of electron temperature and density, the initial
potential of satellite surfaces, and solar cell array potential on the final equilibrium potential reached on
the satellite surfaces.
A concept of using plasmas against low-orbit satellites has recently been proposed based on the
interference and damage effects they have on satellites (Refs. 1, 2). The basic idea is to release a cloud of
high-density plasma in front of a satellite, and when the satellite passes through it, the charged particles in
the plasma will cause the charges carried on the surface of the satellite to form certain potential
differences which will produce surface arc discharges that will disrupt the normal operating state of the
satellite. The plasma will also create reactive power loss in the solar cells, which will debilitate the
electronic equipment on the satellite. This paper will proceed from the aspect of the discharges on a
satellite surface caused by plasma, and through computation analysis will study the feasibility of this idea.

So if that were to happen to a semi-conductor floating in space, like say a rock with crystaline structure of silicates, other minerals and some metals thrown in for good measure, I would expect more of a non-luminous or glow discharge, with the accompanying cathode corona, rather than arcing that happens on a better conductor like a satellite.
Main Belt Comet, passing through a "cloud or filament of plasma" of higher electrostatic potential?
Long and Short period comets would also have a cellular boundary DL, the coma, mitigating the voltage potential between the semiconducting body V- and the surrounding solar plasma stream V+.

Or something like that.