by LaSuisse1 » Mon Feb 03, 2020 4:51 pm
JP Michael wrote: ↑Tue Jan 14, 2020 5:25 am
I have a question about electric comets and more generally planets/stars.
In a NASA image of Comet Holmes it shows several distinct layers and boundaries:
My question is whether these plasmapheric boundaries represent double layers of electrical potential drop?
A secondary question is the physics of the tail-side of the coma where the double layers seem to be breaking down. Would these be apt observations?
Answer to first question: No.
Answer to second question: No.
If you follow the extensive peer-reviewed literature from the Rosetta mission to 67P, as well as the older material from the various probes at Halley, in 1986, you'll find that no such double layers exist. And there is no 'potential drop'.
There are a number of interesting plasma boundaries at comets, and the aforementioned missions were the best equipped to study them. In '86 they were fly-by missions, albeit through a very extensive coma of a particularly active comet. The main boundary of interest, predicted to exist pre-mission, was the diamagnetic cavity boundary. This was duly encountered by Giotto, at ~ 4500 km from the nucleus. This is a boundary where the Interplanetary Magnetic Field (IMF), carried by the solar wind, piles up, and no longer reaches the cometary nucleus. The solar wind itself has long since been getting nowhere near the nucleus. From memory, it died away at ~ 10 000 km at Halley. In other words, it is slowed and deflected due to mass loading from cometary ions. Within the diamagnetic cavity are only neutrals (overwhelmingly) and ions of cometary origin, heading outwards. Mostly neutral water and water ions. The neutrals are not affected by the boundary on the way out, for obvious reasons, while the ions get involved in some interesting stuff. Plenty of literature on that, if you're interested.
Similar was seen at 67P, albeit this was a far less active comet. Therefore the boundaries were a lot closer to the nucleus. The diamagnetic cavity was very unstable but, at peak, was a few hundred km from the nucleus. As this was a much longer lasting mission than the Halley fly-bys, the behaviour of the solar wind could be monitored over a longer timespan. To all intents and purposes, the solar wind disappeared from the location of the spacecraft from ~ 4 months before and after perihelion. An excursion sunward to ~ 1500 km, in October 2015 (# 2 months post-perihelion), failed to detect it. On the way back, it was briefly detected, as the coma was hit by a CME, at 800 km.
Another boundary of interest in the bow shock, which was detected at Halley, but not 67P, although there are indications that it exists. It has also been encountered at other comets.
As for the tail, there was little in the literature before Rosetta, the only mission to directly fly through the tail being the ICE mission to Giacobini-Zinner, in 1985. Previous literature had proposed that double layers may be possible in the tail (but not on the sunward side), mostly by D. A. Mendis.
No such was seen at G-Z, or Halley, although Mendis thought there might have been some indication at the latter. He was probably wrong, and seemed to drop the idea thereafter. Rosetta did have a dedicated tail excursion, and no such indications were seen. There are a few papers in the literature detailing that excursion.
Regarding 'potential drops', I'm not overly sure what you are getting at. Rosetta was equipped with various instruments that would detect such things. It also had a magnetometer, as did Giotto. Inside the diamagnetic cavity at both comets, the magnetic field (as indicated by the name of the cavity!) is seen to drop to zero. The comet itself, of course, has no intrinsic magnetic field. This was also confirmed by the Philae lander at 67P.
Out of interest, the confirmation of the formation of the predicted diamagnetic cavity did not come at a real comet. It was observed during a set of artificial comet experiments performed in space, known as AMPTE, back in 1984-5. If you are interested in that, there is quite a bit in the literature, including;
Dynamics of the AMPTE artificial comet
G. Haerendel, et al.
https://www.researchgate.net/profile/Wo ... c807cf.pdf
Hopefully, that has answered your questions in reasonable detail. There is a lot of literature out there on cometary missions, some of it free access. Worth a read if that is your thing.
[quote="JP Michael" post_id=303 time=1578979514 user_id=30575]
I have a question about electric comets and more generally planets/stars.
In a NASA image of Comet Holmes it shows several distinct layers and boundaries:
[Img]https://apod.nasa.gov/apod/image/0711/Holmes-CFHT_Cuillandre800.jpg[/img]
My question is whether these plasmapheric boundaries represent double layers of electrical potential drop?
A secondary question is the physics of the tail-side of the coma where the double layers seem to be breaking down. Would these be apt observations?
[/quote]
Answer to first question: No.
Answer to second question: No.
If you follow the extensive peer-reviewed literature from the Rosetta mission to 67P, as well as the older material from the various probes at Halley, in 1986, you'll find that no such double layers exist. And there is no 'potential drop'.
There are a number of interesting plasma boundaries at comets, and the aforementioned missions were the best equipped to study them. In '86 they were fly-by missions, albeit through a very extensive coma of a particularly active comet. The main boundary of interest, predicted to exist pre-mission, was the diamagnetic cavity boundary. This was duly encountered by Giotto, at ~ 4500 km from the nucleus. This is a boundary where the Interplanetary Magnetic Field (IMF), carried by the solar wind, piles up, and no longer reaches the cometary nucleus. The solar wind itself has long since been getting nowhere near the nucleus. From memory, it died away at ~ 10 000 km at Halley. In other words, it is slowed and deflected due to mass loading from cometary ions. Within the diamagnetic cavity are only neutrals (overwhelmingly) and ions of cometary origin, heading outwards. Mostly neutral water and water ions. The neutrals are not affected by the boundary on the way out, for obvious reasons, while the ions get involved in some interesting stuff. Plenty of literature on that, if you're interested.
Similar was seen at 67P, albeit this was a far less active comet. Therefore the boundaries were a lot closer to the nucleus. The diamagnetic cavity was very unstable but, at peak, was a few hundred km from the nucleus. As this was a much longer lasting mission than the Halley fly-bys, the behaviour of the solar wind could be monitored over a longer timespan. To all intents and purposes, the solar wind disappeared from the location of the spacecraft from ~ 4 months before and after perihelion. An excursion sunward to ~ 1500 km, in October 2015 (# 2 months post-perihelion), failed to detect it. On the way back, it was briefly detected, as the coma was hit by a CME, at 800 km.
Another boundary of interest in the bow shock, which was detected at Halley, but not 67P, although there are indications that it exists. It has also been encountered at other comets.
As for the tail, there was little in the literature before Rosetta, the only mission to directly fly through the tail being the ICE mission to Giacobini-Zinner, in 1985. Previous literature had proposed that double layers may be possible in the tail (but not on the sunward side), mostly by D. A. Mendis.
No such was seen at G-Z, or Halley, although Mendis thought there might have been some indication at the latter. He was probably wrong, and seemed to drop the idea thereafter. Rosetta did have a dedicated tail excursion, and no such indications were seen. There are a few papers in the literature detailing that excursion.
Regarding 'potential drops', I'm not overly sure what you are getting at. Rosetta was equipped with various instruments that would detect such things. It also had a magnetometer, as did Giotto. Inside the diamagnetic cavity at both comets, the magnetic field (as indicated by the name of the cavity!) is seen to drop to zero. The comet itself, of course, has no intrinsic magnetic field. This was also confirmed by the Philae lander at 67P.
Out of interest, the confirmation of the formation of the predicted diamagnetic cavity did not come at a real comet. It was observed during a set of artificial comet experiments performed in space, known as AMPTE, back in 1984-5. If you are interested in that, there is quite a bit in the literature, including;
Dynamics of the AMPTE artificial comet
G. Haerendel, et al.
https://www.researchgate.net/profile/Wolfgang_Baumjohann/publication/230562439_Dynamics_of_the_AMPTE_artificial_comet/links/53da42980cf2631430c807cf.pdf
Hopefully, that has answered your questions in reasonable detail. There is a lot of literature out there on cometary missions, some of it free access. Worth a read if that is your thing.