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The Breakup of C/1999 S4 (LINEAR): Days 0-10

The Breakup of C/1999 S4 (LINEAR): Days 0-10. Mark Kidger Instituto de Astrofísica de Canarias. Was C/1999 S4 a normal comet?. It was dynamically new, but: had depleted low-temperature volatiles 3rd power brightening with r unusually large non-gravitational parameters

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The Breakup of C/1999 S4 (LINEAR): Days 0-10

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  1. The Breakup of C/1999 S4 (LINEAR): Days 0-10 Mark Kidger Instituto de Astrofísica de Canarias

  2. Was C/1999 S4 a normal comet? • It was dynamically new, but: • had depleted low-temperature volatiles • 3rd power brightening with r • unusually large non-gravitational parameters • C/1999 S4: A1=9.26, A2=-1.7054, m 8.0 log r • C/1996 B2: A1=2.56, A2= 0.0485, m 8.7 log r • C/2001 A2: A1=0.47, A2=-0.3558, m 7.5 log r • C/1995 O1: A1=1.25, A2= 0.1283, m 10.0 log r • A dynamically new comet usually has m 13-18 log r at large r.

  3. Fragmentation history? • Weaver et al. reported a factor of 7 variation in flux in 2.2 days in a 0.15” aperture with HST. • Broad band CCD photo-metry (10” aperture) shows two possible events consistent with fragmentations. • Probably the comet was fragmenting constantly from discovery.

  4. July 23rd - 26th: outburst to bust Anticlockwise from the left: July 23.9, July 24.9, July 25.9, and July 26.9. 11 arcmin

  5. Contour maps from July 24-27th • There was a spectacular drop in surface brightness. • The centre of light drifted rapidly in the anti-sun direction. 40 arcsec

  6. A deep image with the 2.5-m Isaac Newton Telescope on August 1.9 shows no discrete nuclei down to B=22.5 This implies that any surviving nuclei had HV>25.0 at this time. This implies a limiting size of a few metres for actively subliming icy nuclei 80-m for silicate nuclei of albedo 5%. The brightest nuclei reported by Weaver et al. had HV27.

  7. The same image shows a distinctive “lance point” shape very clearly. This is seen in all the images from July 26th. It is at the nominal position of the comet and indicates the presence of a surviving dust-emitting source.

  8. Conclusions (I) • C/1999 S4 looks more like an icy asteroid than a rocky comet • Isotope ratios suggest formation in the trans-Saturnian region • How was it expelled into a near parabolic orbit (1/a (original)=0.000040)? • But, the disintegration suggests that the nucleus was an extremely loosely bound conglomerate (a “polverón”).

  9. Recent fragmentation of 51P • Two fragments of similar apparent brightness • Tendency for “d” to brighten slightly compared to “a” • Fragmentation in July? (Sekanina estimated early Sept.)

  10. Conclusions II • Experience suggests that comet nuclei are of a wide range of types (consolidated rubble piles, fragile rubble piles, through to “dust balls”). • The solidity is presumably due to the circumstances of formation. • SL9, C/1999 S4, C/2001 A2, etc. suggest that there is a continuous range in properties from rocky asteroids to icy comets.

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