Size of Holmes's Coma (APOD 17 Nov 2007)

[Chris Peterson]

Reports about the comet tend to run a little late, but today's APOD is substantially off in its estimate of coma size. As of November 17, the dust coma is 2.5 million kilometers in diameter, not 1.4 million. That makes it 80% larger than the Sun. I've been measuring the growth since the first day of the outburst. The coma will exceed twice the size of the Sun on November 20.

[kovil]

Is the 'dust' of Holmes' coma 'finely divided' dust?

Has there been any determination of the constituents in terms of elements in Holmes' coma dust?

Would its occulting or eclipsing of star Mirafak (sp) on Monday lend any help in determination by starlight absorption lines etc.?

"I say Holmes, what a mystery we've got here, eh what?"
"Just what the doctor ordered, so to speak Watson."

[craterchains]

Thank you Chris,
Now this is the kind of data that is very much appreciated. What is your estimate of central core size? ahhh yes, 3.4k,

[kovil]

Chris,

When you say << "That outer coma is mostly gas rather than dust. The growth rate of the coma initially appeared linear, but now seems to be showing a very slight increase with time. The initial dust ejection velocity was about 500 meters per second from the nucleus (similar to what was measured for comets Hyakutake and Hale-Bopp at their most active), but the outer zone of the coma is now increasing in radius at over 700 m/s. This is difficult to explain, but may be related to increased dispersion caused by the solar wind." >>

Could your word 'gas' also be a euphemism for 'plasma'. If Holmes is outgassing plasma, the Sun's electric field in the solar system, which accelerates the solar wind, would also be accelerating Holmes' outgassed plasma. This would easily explain why the coma is increasing its size at an increasing rate. The plasma is being accelerated by the electric field.

I am looking forward to see if Holmes will be making any electrical plasma displays as it nears the Sun. Will it have a braided tail?

If Holmes is 3.4 km diameter, what kind of total electrical capacitance could that volume of material contain? Would it largely depend on what that material is? Do different materials have differing electrical capacitance storage properties?

On second thought the coma would be being accelerated away from the Sun, not tangentially, as it is being measured to do in its 700 m/s, as you say. Could the material in the coma be electrically repelling itself as it 'charges up' in the solar e-field?

Questions from 4am here in the Nevada high desert. The skies are clear, but the unaided eye doesn't really see Holmes. Auriga, Cassiopeia and the Pleiades are easily spotted, but Perseus is a new one to me.

Are they any estimates on how far away Holmes is from the Sun? Is it closer than Saturn's orbit? Or is it nearer to Mars orbital distance from the Sun?

[BMAONE23]

Holmes orbits between Mars and Jupiter and is slightly inclined to the eclliptic. It is currently just past its closest approach to the sun and is slowly getting farther away.

[Chris Peterson]

Could your word 'gas' also be a euphemism for 'plasma'. If Holmes is outgassing plasma, the Sun's electric field in the solar system, which accelerates the solar wind, would also be accelerating Holmes' outgassed plasma. This would easily explain why the coma is increasing its size at an increasing rate. The plasma is being accelerated by the electric field.

Certainly, the gas is partly ionized by its interaction with the charged particles of the solar wind, meaning it can be considered a plasma. However, the Sun has no substantial electric field- at least, not one with significant influence across a large distance. The ionized gas around the comet is affected by the Sun's magnetic field, however. I don't think the increased rate of dust expansion is caused by anything more than diffusion. Energy from the Sun, both in the form of EM and charged particles, increases the kinetic energy of dust particles.

I am looking forward to see if Holmes will be making any electrical plasma displays as it nears the Sun.

It doesn't get much nearer the Sun that it is right now.

On second thought the coma would be being accelerated away from the Sun, not tangentially, as it is being measured to do in its 700 m/s, as you say. Could the material in the coma be electrically repelling itself as it 'charges up' in the solar e-field?

Again, there is essentially no solar e-field. The highly isotropic nature of the expansion (apparently, since we see things from only one viewpoint) argues for a diffusive process that isn't strongly affected by the solar wind or solar magnetic field. With most active comets, these things shred the coma into a long tail. That apparently isn't happening with 17P.

Are they any estimates on how far away Holmes is from the Sun? Is it closer than Saturn's orbit? Or is it nearer to Mars orbital distance from the Sun?

17P is in a moderately inclined orbit between Mars and Jupiter. It is currently 2.4 AU from the Sun.

[Chris Peterson]

Is the 'dust' of Holmes' coma 'finely divided' dust?

I'm not sure what you mean by that, but the dust is certainly very fine. I'm planning on trying to estimate the size of the dust using the basic equations defining comet dust ejection velocities, but haven't had time yet for this.

Has there been any determination of the constituents in terms of elements in Holmes' coma dust?

Not that I've heard, although there probably isn't any reason to expect anything unusual. The comet has been examined spectroscopically, which has provided information about the gaseous components. The dust has basically just shown the spectrum of the reflected sunlight.

Would its occulting or eclipsing of star Mirafak (sp) on Monday lend any help in determination by starlight absorption lines etc.?

In principle it could. In practice, probably not. And only for gas, not dust. Since dust is opaque, it needs to be examined in reflected light, not transmitted.

[iamlucky13]

In principle it could. In practice, probably not. And only for gas, not dust. Since dust is opaque, it needs to be examined in reflected light, not transmitted.

What about by diffraction? It seems to me that measurements of particle size in Saturn's rings was made by occultation, but perhaps I'm confused and it was just spatial density.

[kovil]

Thanks Chris for all the info and your work to gather it.

I didn't realize Holmes, (and I appreciate your calling it Holmes and not Comet Holmes) only orbited the Sun between the orbits of Jupiter and Mars, so it therefore does not qualify to be called a Comet, like all the media is calling it. (more misleading disinformation by the standard theorists trying to keep the general public from knowing or thinking in Truth)

The question of the moment is, Where is Holmes in its orbit in respect to out of plane with the planets? Is Holmes near the northern most apex of its tilted orbit with respect to the general orbital plane of the planets? If so this may be why Holmes is putting on a display, as it wanders around in the reasonably same neighborhood the rest of the time and doesn't exhibit behaviour like this normally. If it lives its life between Mars and Jupiter, why is it effusing like this now? There is a reason, and our mission if we decide to take it, is to discover that or those reasons.



Hi Harry, check you APOD PM's. Good to be back, and to see you are here too! I'm becoming like you in that there are too many things tugging for my attention these days. Cheers!

[Chris Peterson]

I didn't realize Holmes, (and I appreciate your calling it Holmes and not Comet Holmes) only orbited the Sun between the orbits of Jupiter and Mars, so it therefore does not qualify to be called a Comet, like all the media is calling it.

It is a comet by any accepted definition. Comets are just small bodies that contain volatiles that can evaporate off. When evaporation is occurring, we say the comet is active; when the comet is far from the Sun and there is little or no evaporation, it is inactive. Eventually, a comet evaporates away all its volatiles, and it is either called a dead comet or an asteroid. There are billions of comets in the Oort cloud that never come into the inner Solar System at all. They're still considered comets.

The question of the moment is, Where is Holmes in its orbit in respect to out of plane with the planets? Is Holmes near the northern most apex of its tilted orbit with respect to the general orbital plane of the planets?

It is near its northernmost out-of-plane position.

If so this may be why Holmes is putting on a display, as it wanders around in the reasonably same neighborhood the rest of the time and doesn't exhibit behaviour like this normally.

That shouldn't have anything to do with it. The comet doesn't "wander around"; it is in a short period orbit and if follows the same path every 7 years. In terms of position, nothing is different now than it has been many times in the past.

If it lives its life between Mars and Jupiter, why is it effusing like this now?

That's uncertain. There are several plausible reasons, however. A minor collision with co-orbital material could have exposed fresh surface. Heat absorbed during it last perihelion, a few months ago, may have reached a volatile pocket, which expanded and caused a surface shift. Gravitational effects from the planets (mainly Jupiter) may have caused a surface shift or disruption. It is likely that at least some comets are little more than loosely clumped collections of dust, gravel, and ice.

[kovil]

Many thanks Chris,

In terms of Electric Theory, they would hypothesize that Holmes, in its northernmost venturing in its orbit, would possibly be encountering a different area of the solar e-field, and that is the reason Holmes became active.

I understand that you, and most of us, have the standard solar and cometary model as our point of view and reference when we make our interpretation of observed events. I have no problem with anyones right to choice of views. I on the other hand have a new viewpoint, Electric Theory, and that interprets the data differently.

It will be interesting to watch Holmes and as its orbit takes it southward, after Holmes descends 5 degrees (as a guess), will its effervescent behaviour diminish and disappear? (as it would have left that area of the solar e-field that caused its effusive behaviour in the first place!)

Holmes is certainly a very interesting object to observe, and quite a number of explanations have been put forth to account for its activity!

Onward to the discovery of the Truth!

One project which I am championing is a polar orbital probe of the Sun, at the radius of Venus or so. A long term project yes, but it would possibly answer some questions about what is happening in the inter-solar-system medium which is far-tangent to the planetary orbital plane. (Now if I could just learn the gentle art of writing govt. grants !)

[Pete]

Hi kovil & everyone,
A project similar to the one you propose has actually been in polar orbit around the Sun since 1990: Ulysses (wiki article), by NASA/ESA. My search results have turned up observations of the Sun's magnetic rather than electric field by Ulysses, probably because, as Chris mentioned, the Sun's electric field is negligible.

[Chris Peterson]

In terms of Electric Theory, they would hypothesize that Holmes, in its northernmost venturing in its orbit, would possibly be encountering a different area of the solar e-field, and that is the reason Holmes became active.

The idea that the Sun's weak electric field has any significant influence outside its own atmosphere runs contrary to observation.

That said, the trick to understanding the behavior of 17P lies not just in explaining why it produced an outburst this year and 115 years ago, but why it didn't in the sixteen other times between that it came around. Its orbit hasn't changed; it's passed through the same parts of the Solar System, and the same distance out of the ecliptic. The cause of the outburst is more complex than just where the comet orbits.