Dave T said: the Electric model is not complete in its explanation of the distinction between comets and asteroids
David Talbott wrote:Nereid this is helpful info, though I keep wondering if there's a clear message in the data as a whole. I certainly believe Wal's inclusion of "forbidden lines" [OI] apparent in Austin's coma was a valuable pointer, but more a pointer to a line of investigation that has never been adequately carried out.
From the EU perspective, the good news is, I guess, that there's a lot of good, quantitative data already published in the literature, so once EU models have been developed sufficiently, they may be able to be tested quite quickly.
Lloyd wrote:* Is a large part of the EU explanation that asteroids are in electrical [charge] equilibrium with their environment, while comets are not, and the reason being usually that comets, being on elliptical orbits, encounter a changing charge environment, while asteroids on less eccentric orbits do not?
Except from the more extreme eccentric orbits by some comets, there exists both asteroids and comets of the same elliptical orbit, displaying different effects (tail vs no tail).
mharratsc, you're right, and I think I may have rushed my argument, and it was based on a list of refutations I read at the JREF a while back.
http://forums.randi.org/showpost.php?p= ... tcount=395
I realize it's a strawman: "because there are 6-7 mainbelt comets, they represent ALL comets, and therefore the hundreds of thousands asteroids with orbits of same/more eccentricity should also display cometary effects."
Now that is a blunt argument, because mainbelt comets are humbly thought by many astrophysicists to be "a little odd" in their behaviour, and the 6-7 mainbelt comets surely don't represent the thousands of reported comets, and trillions of estimated comets thought to exist within the solar system, of completelly different orbits.
So what might have happened to Comet Holmes? It is not a typical comet. The eccentricity of its orbit is minimal. It is always outside the orbit of Mars and inside the orbit of Jupiter. In fact, it is virtually as close to being an asteroid as it is to being a comet. And astronomers are slowly realizing that the distinctions between asteroids and comets are not as clear as they had once believed. Occasionally, asteroids sport cometary tails, like the asteroid Chiron, which was seen to develop a tail while orbiting between Saturn and Uranus around 1988 and 1989. It is now officially classified as both an asteroid and a comet. Since the electrical stresses on Holmes would be minimal, much like those on asteroids with modestly elliptical orbits, it is not unreasonable to assume that its plasma sheath remains largely undisturbed -- unless it penetrates into or is penetrated by another sheath with sufficient differential across its double layer to cause an explosive breakdown.
It's interesting to note that the diagram of Holmes' orbit shows that it crossed the ecliptic (the plane of the planets movement around the Sun) quite close to the time of its closest approach to Mars. So it is certainly conceivable that Mars' own plasma sheath, by penetrating that of Holmes, provoked the fateful breakdown. Though this would not qualify as a coherent hypothesis today, it is the kind of issue raised by the electric model that is systematically ignored by mainstream astronomers.
In a private email, Thornhill suggested that:
"Outbursts from comets at great distances from the Sun seem to be correlated with a sudden change in the solar 'wind' plasma environment due to a solar storm. The point about sudden comet outbursts is that we are dealing with a sudden, discontinuous process of plasma discharge - a switch from dark current mode to normal glow mode. It is a complex surface phenomenon that cannot be predicted. The best we can do is to say that the passage of a sudden change in the solar wind is the most likely time to see a flareup."
The sun had been electrically active in the days before the "explosion". Upon investigation of data from the ACE satellite, see this movie or this graph, Michael Mozina noticed that there was a large spike in the density of the solar wind on October 22 at 19:45, two days before the infamous flareup. This spike likely switched the comet into normal glow mode and allowed it to grow. Once in normal glow mode, the plasma coma does not require a sustained voltage to maintain that mode.
http://www.thunderbolts.info/thunderblo ... _swall.htm
Siggy_G wrote:The other part that needs clarification is the measured/calculated density of asteroids versus comets. Asteroids are heavier/denser based on orbital calculations (velocity). Whether (dis)charge mechanisms affect the oribital velocity, and how, needs elaboration. I wondered whether drag effect ("aerodynamics") from the interplanetary medium could give a counter acceleration, but while the effect surely is there, calculations showed it to be way too tiny to have any significant impact on a massive comet. (For solar sails and low density objects on the other hand...).
http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?p=323#p323Posted: Mon Nov 26, 2007 7:30 pm Post subject: non-gravitational forces/mainstream Reply with quote
non-gravitational forces : Forces that are not of gravitational origin which act on asteroids and comets and that can sometimes significantly alter their orbits. Examples include reaction forces due to outgassing of volatile materials and the Yarkovsky and Poynting–Robertson forces.
Poynting–Robertson effect: A deacceleration and spiraling inward of small dust particles orbiting the Sun due to their interaction with solar radiation.
Yarkovsky effect : Acceleration due to recoil force caused by the thermal reradiation from an irregular object. This can cause substantial changes to asteroidal orbits and also affect their rotational states.
nick c wrote:Comet Holmes 17P, which flared up in the late 1800's and then again in 2007, qualifies as one example of this type of object. It's orbit is entirely between the orbits of Jupiter and Mars, that is in the asteroid belt.
Close approaches to planets: During the 20th century, this comet made two close approaches to Jupiter. There are also two close approaches to Jupiter during the 21st century. (From the orbital work of Kazuo Kinoshita and G. W. Kronk)
0.54 AU from Jupiter on 1908 December 9
increased perihelion distance from 2.12 AU to 2.34 AU
increased orbital period from 6.86 to 7.33 years
1.03 AU from Jupiter during 1968 April
decreased perihelion distance from 2.35 AU to 2.16 AU
decreased orbital period from 7.35 to 7.05 years
1.50 AU from Jupiter during 2004 January
decreased perihelion distance from 2.17 AU to 2.05 AU
decreased orbital period from 7.07 to 6.88 years
0.85 AU from Jupiter on 2051 April 8
increased perihelion distance from 2.06 AU to 2.21 AU
increased orbital period from 6.89 to 7.21 years
The comet is Tempel 1, which NASA's Deep Impact probe visited in 2005. Now another NASA spacecraft, Stardust-NExT, is closing in for a second look on Valentine's Day, Feb. 14, 2011.
Stardust-NExT will reveal how the plateau has changed (Is it flowing?), helping the team determine its origin. Whatever their origin, the plateau and layering show that comets have a much more complicated geologic history than previously thought.
It's a history NASA has had a hand in. During its 2005 visit, Deep Impact dropped an 820-pound projectile into the comet's core. In a development that surprised mission scientists, the impact excavated so much material that the underlying crater was hidden from view. Deep Impact's cameras were unable to see through the enormous cloud of dust the impactor had stirred up. Stardust NExT could provide a long anticipated look at the impact site.
NASA's Stardust spacecraft returned new images of a comet showing a scar resulting from the 2005 Deep Impact mission. The images also showed the comet has a fragile and weak nucleus.
"We see a crater with a small mound in the center, and it appears that some of the ejecta went up and came right back down," said Pete Schultz of Brown University, Providence, R.I. "This tells us this cometary nucleus is fragile and weak based on how subdued the crater is we see today."
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