View Full Version : Comet C/2007 N3 Lulin - A Twist In The Tail

2009-Feb-02, 01:30 AM
When Chi-Sheng Lin of Taiwan's Institute of Astronomy captured three images on July 11, 2007 with something strange in them, it was first believed he'd picked up just another asteroid. But, by July 17 astronomers in Table Mountain Observatory, California were noticing a coma 2-3" across, with a bright central core. That's not [...]

More... (http://www.universetoday.com/2009/02/01/comet-c2007-n3-lulin-a-twist-in-the-tail/)

2009-Feb-02, 02:30 PM
Mendis, D. A. & Rosenberg, M. suggested that instabilities in cometary tails may be formed due to:

The presence of charged dust in a plasma can both modify the behavior of usual plasma instabilities and lead to the appearance of new instabilities. Since dust grains are subject to non-electromagnetic forces such as gravity, friction, or radiation pressure, there can be new sources of free energy to drive instabilities, including relative drifts between the charged dust and the lighter plasma particles (electrons and ions) in cosmic dusty plasma environments (e.g. Tsytovich et al 1990). [..] The Kelvin-Helmholtz instability can occur in a plasma when there is a gradient in the fluid flow speed between adjacent fluid layers, as happens for example in the cometary environment -- Mendis, D. A. & Rosenberg, M., "Cosmic Dusty Plasmas", Annual Review of Astronomy and Astrophysics, Volume 32, 1994, pp. 419-463. Section 5.2 "Instabilities (http://articles.adsabs.harvard.edu//full/1994ARA%26A..32..419M/0000456.000.html)" (online in full)

The news article (http://www.universetoday.com/2009/02/01/comet-c2007-n3-lulin-a-twist-in-the-tail/) mentions that "Is it possible that the kink in the tail is an instability resulting from currents flowing along the tail axis", and Mendis also identifies a cometary current system including plasma tail streamers separated by a neutral current sheet, with a total current exceeding 108Amps. -- Mendis, D. A., "On the hydromagnetic model of comets (http://adsabs.harvard.edu/abs/1978M%26P....18..361M)" (1978) Moon and the Planets, vol. 18, May 1978, p. 361-369. (online in full)

The only other comet that I know of, that had an anti-tail, was Comet Arend-Roland, discovered in 1957. -- Opik, E. J., "Spike of Comet Arend-Roland 1956 (http://adsabs.harvard.edu/abs/1958IrAJ....5...37O), (1958) Irish Astronomical Journal, vol. 5(2/3), p. 37. (online in full)

However, the cometary anti-tail does not seem to be consistent with the idea that cometary tails are due just to the pressure of the Solar Wind, but due to other interactions of the cometary dust particles with the plasma in the solar wind, which I have summarised on the "Comets" page my own site (http://www.plasma-universe.com/index.php/Comet) from peer-reviewed sources.