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TOPIC: Comet 17P/Holmes


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Comet 17P/Holmes
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Title: Why did Comet 17P/Holmes burst out?
Authors: W. J. Altenhoff, E. Kreysa, K. M. Menten, A. Sievers, C. Thum, A. Weiss

Based on millimetre-wavelength continuum observations we suggest that the recent 'spectacle' of comet 17P/Holmes can be explained by a thick, air-tight dust cover and the effects of H2O sublimation, which started when the comet arrived at the heliocentric distance <= 2.5 AU. The porous structure inside the nucleus provided enough surface for additional sublimation, which eventually led to the break up of the dust cover and to the observed outburst. The magnitude of the particle burst can be explained by the energy provided by insolation, stored in the dust cover and the nucleus within the months before the outburst: the subliming surface within the nucleus is more than one order of magnitude larger than the geometric surface of the nucleus -- possibly an indication of the latter's porous structure. Another surprise is that the abundance ratios of several molecular species with respect to H2O are variable. During this apparition, comet Holmes lost about 3% of its mass, corresponding to a 'dirty ice' layer of 20m.

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RE: Comet 17P/Holmes
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NASAs Spitzer Space Telescope has deeply observed comet Holmes to find out why it suddenly exploded in 2007.
Observations taken of the comet by Spitzer deepen the mystery, showing oddly behaving streamers in the shell of dust surrounding the nucleus of the comet.
The data also offer a rare look at the material liberated from within comet Holmes nucleus, and confirm previous findings from NASAs Stardust and Deep Impact missions.

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Anatomy of a Busted CometIn an attempt to understand these odd occurrences, astronomers pointed NASA's Spitzer Space Telescope at the comet in November 2007 and March 2008. By using Spitzer's infrared spectrograph instrument, Reach was able to gain valuable insights into the composition of Holmes' solid interior. Like a prism spreading visible-light into a rainbow, the spectrograph breaks up infrared light from the comet into its component parts, revealing the fingerprints of various chemicals.

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When comet Holmes unexpectedly erupted in 2007, professional and amateur astronomers around the world turned their telescopes toward the spectacular event. Their quest was to find out why the comet had suddenly exploded.
Observations taken of the comet after the explosion by NASA's Spitzer Space Telescope deepen the mystery, showing oddly behaving streamers in the shell of dust surrounding the nucleus of the comet. The data also offer a rare look at the material liberated from within the nucleus, and confirm previous findings from NASA's Stardust and Deep Impact missions.

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In October, fix your stares on the sky to watch the sporadic comet '17P/HOLMES'. Throughout October and November, it will be visible in the Northern Hemisphere. The comet is visible in India and is rightly regarded as 'morning comet'. The comet could be seen in Mysore at about 1:00 am to 4:50 am.

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Ephemeris

Date TT R. A. (2000) Decl. Delta r Elong. Phase mag mag
2008 10 11 09 03.22 +26 28.6 4.149 3.882 67.7 13.8 20.8
2008 10 16 09 06.77 +26 15.1 4.096 3.900 71.7 14.0 20.8
2008 10 21 09 09.99 +26 03.0 4.040 3.917 75.9 14.3 20.8
2008 10 26 09 12.87 +25 52.3 3.982 3.935 80.1 14.4 20.8
2008 10 31 09 15.38 +25 43.2 3.923 3.953 84.5 14.5 20.8
2008 11 05 09 17.50 +25 35.8 3.863 3.970 88.9 14.5 20.7
2008 11 10 09 19.21 +25 30.1 3.803 3.987 93.5 14.4 20.7
2008 11 15 09 20.49 +25 26.2 3.743 4.005 98.1 14.2 20.7
2008 11 20 09 21.34 +25 24.0 3.684 4.022 102.9 13.9 20.6
2008 11 25 09 21.72 +25 23.8 3.626 4.039 107.8 13.5 20.6
2008 11 30 09 21.62 +25 25.2 3.570 4.056 112.8 13.0 20.6



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Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   m1 
2008 05 04 05 29.00 +35 43.9 3.939 3.251 41.4 11.8 20.7
2008 05 09 05 37.16 +35 33.2 4.004 3.272 38.3 11.0 20.7
2008 05 14 05 45.31 +35 22.0 4.066 3.293 35.3 10.2 20.8
2008 05 19 05 53.45 +35 10.3 4.125 3.314 32.3 9.4 20.9
2008 05 24 06 01.56 +34 57.8 4.180 3.335 29.4 8.6 21.0
2008 05 29 06 09.63 +34 44.7 4.232 3.356 26.5 7.7 21.0


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Date TT R. A. (2000) Decl. Delta r Elong. Phase m1 
2008 03 05 03 55.92 +37 48.1 2.992 2.993 80.6 19.1 19.5
2008 03 10 04 02.97 +37 34.6 3.078 3.015 77.1 18.7 19.6
2008 03 15 04 10.21 +37 22.4 3.164 3.037 73.6 18.3 19.7
2008 03 20 04 17.63 +37 11.1 3.248 3.058 70.2 17.8 19.8
2008 03 25 04 25.19 +37 00.6 3.332 3.080 66.9 17.3 19.9
2008 03 30 04 32.89 +36 50.7 3.415 3.101 63.5 16.8 20.0


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Date TT R. A. (2000) Decl. Delta r Elong. Phase m1 
2008 02 04 03 19.47 +39 48.4 2.480 2.863 102.7 19.6 18.8
2008 02 09 03 24.68 +39 22.4 2.563 2.885 98.9 19.7 18.9
2008 02 14 03 30.29 +38 59.1 2.648 2.907 95.1 19.8 19.1
2008 02 19 03 36.26 +38 38.3 2.733 2.928 91.4 19.7 19.2
2008 02 24 03 42.54 +38 19.7 2.819 2.950 87.7 19.6 19.3
2008 02 29 03 49.11 +38 03.0 2.905 2.972 84.1 19.4 19.4


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Title: The comet 17P/Holmes 2007 outburst: the early motion of the outburst material
Authors: M. Montalto (1), A. Riffeser (2), U. Hopp (1 and 2), S. Wilke (2), G. Carraro (3) ((1) MPE, Munchen, Germany, (2) Universitats-Sternwarte Munchen, Germany, (3) ESO Santiago)

Context. On October 24, 2007 the periodic comet 17P/Holmes underwent an astonishing outburst that increased its apparent total brightness from magnitude V ~17 up to V ~2.5 in roughly two days. We report on Wendelstein 0.8 m telescope (WST) photometric observations of the early evolution stages of the outburst.
Aims. We studied the evolution of the structure morphology, its kinematic, and estimated the ejected dust mass.
Methods. We analysed 126 images in the BVRI photometric bands spread between 26/10/2007 and 20/11/2007. The bright comet core appeared well separated from that one of a quickly expanding dust cloud in all the data, and the bulk of the latter was contained in the field of view of our instrument. The ejected dust mass was derived on the base of differential photometry on background stars occulted by the moving cloud.
Results. The two cores were moving apart from each other at a relative projected constant velocity of (9.87 0.07) arcsec/day (0.135 0.001 km/sec). In the inner regions of the dust cloud we observed a linear increase in size at a mean constant velocity of (14.60.3) arcsec/day (0.2000.004 km/sec). Evidence of a radial velocity gradient in the expanding cloud was also found. Our estimate for the expanding coma's mass was of the order of 10^{-2}-1 comet's mass implying a significant disintegration event.
Conclusions. We interpreted our observations in the context of an explosive scenario which was more probably originated by some internal instability processes, rather than an impact with an asteroidal body. Due to the peculiar characteristics of this event, further observations and investigations are necessary in order to enlight the nature of the physical processes that determined it.

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