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RE: Periodic Comets
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Title: Secular Light Curve of 2P/Encke: A Comet Active At Aphelion
Authors: Ignacio Ferrin

We present the secular light curve of comet 2P/Encke in two phase spaces, the log plot, and the time plot. The main conclusions of this work are: a) The comet shows activity at perihelion and aphelion, caused by two different active areas: Source 1, close to the South pole, active at perihelion, and Source 2, at the North pole, centred at aphelion. b) More than 18 physical parameters are measured from the secular light curves, many of them new, and are listed in the individual plots of the comet. Specifically we find for Source 1 the location of the turn on and turn off points of activity, RON= -1.630.03 AU, ROFF= +1.490.20 AU, TON= -875 d, TOFF= +9415 d, the time lag, LAG(q)= 6+-1 d, the total active time, TACTIVITY= 18116 d, and the amplitude of the secular light curve, ASEC(1,1) = 4.80.1 mag. c) From this information the photometric age and the time-age defined in Ferrin (Icarus 178, 493-516, 2005a, and Icarus, 185, 523-543, 2006), can be calculated, and we find P-AGE=978 comet years and T-AGE= 1039 comet years (cy). Thus comet 2P/Encke is an old comet entering the methuselah stage (100 cy < age). d) The activity at aphelion (Source 2), extends for TACTIVITY = 81530 d and the amplitude of the secular light curve is ASEC (1,Q) = 3.00.2 mag. e) From a new phase diagram an absolute magnitude and phase coefficient for the nucleus are determined, and we find RNUC(1,1,0)= 15.050.14, and betha= 0.0660.003. From this data we find a nucleus effective diameter DEFFE = 5.12(+2.5;-1.7) km. These values are not much different from previous determinations but exhibit smaller errors. Additional results appear in the full abstract.

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Still image from a visualization of Comet Encke.



NASA's STEREO satellite captured the first images ever of a collision between a solar "hurricane", called a coronal mass ejection (CME), and a comet. The collision caused the complete detachment of the comet's plasma tail.

Series of four still images taken from an animation showing Comet Encke flying through a solar storm as observed by the STEREO satellite.

This series of four still images were taken from a visualization of Comet Encke flying through the solar storm as witnessed by the STEREO satellite. Note Encke's tail being torn off by the coronal mass ejection in the third still above.
Credit: NASA


+ View larger image
+ View close-up visualization (6Mb .avi)
+ View full visualization (7Mb .mpg)


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Chandra Comet Survey
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Title: Spectral Analysis of the Chandra Comet Survey
Authors: D. Bodewits, D.J. Christian, M. Torney, M. Dryer, C.M. Lisse, K. Dennerl, T.H. Zurbuchen, S.J. Wolk, A.G.G.M. Tielens, R. Hoekstra

We present results of the analysis of cometary X-ray spectra with an extended version of our charge exchange emission model (Bodewits et al. 2006). We have applied this model to the sample of 8 comets thus far observed with the Chandra X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1 (LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005 (Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include a broad variety of comets, solar wind environments and observational conditions. The interaction model is based on state selective, velocity dependent charge exchange cross sections and is used to explore how cometary X-ray emission depend on cometary, observational and solar wind characteristics. It is further demonstrated that cometary X-ray spectra mainly reflect the state of the local solar wind. The current sample of Chandra observations was fit using the constrains of the charge exchange model, and relative solar wind abundances were derived from the X-ray spectra. Our analysis showed that spectral differences can be ascribed to different solar wind states, as such identifying comets interacting with (I) fast, cold wind, (II), slow, warm wind and (III) disturbed, fast, hot winds associated with interplanetary coronal mass ejections. We furthermore predict the existence of a fourth spectral class, associated with the cool, fast high latitude wind.

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Periodic Comets
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Researchers have found that comets show a periodic change in brightness linked with the rotation of the sun.
Using 600 observations of brightness outbursts of comets between 1927-2004, a mean period of brightness outburst activity of comets was determined.
The value of this period is T = 6.8d (+/-) 0.6d. Since 4T = 27d

The Rotation period of the Sun at the equator is about 25.3800 days, the Polar Regions rotate once in about 35 days.
Carrington Rotations (the sunspot `zone`) rotate every 27.28 days...

So it seems the comets brightness are linked (obviously) to the sunspots and solar outbursts...


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