Evidence for fresh frost layer on the bare nucleus of comet Hale--Bopp at 32 AU distance

Abstract

Here we report that the activity of comet Hale--Bopp ceased between late 2007 and March, 2009, at about 28 AU distance from the Sun. At that time the comet resided at a distance from the Sun that exceeded the freeze-out distance of regular comets by an order of magnitude. A Herschel Space Observatory PACS scan was taken in mid-2010, in the already inactive state of the nucleus. The albedo has been found to be surprisingly large (8.1$\pm$0.9%{}), which exceeds the value known for any other comets. With re-reduction of archive HST images from 1995 and 1996, we confirm that the pre-perihelion albedo resembled that of an ordinary comet, and was smaller by a factor of two than the post-activity albedo. Our further observations with the Very Large Telescope (VLT) also confirmed that the albedo increased significantly by the end of the activity. We explain these observations by proposing gravitational redeposition of icy grains towards the end of the activity. This is plausible for such a massive body in a cold environment, where gas velocity is lowered to the range of the escape velocity. These observations also show that giant comets are not just the upscaled versions of the comets we know but can be affected by processes that are yet to be fully identified.

arXiv comment7 pages, 6 figures, accepted for publication in ApJ

References in corpus (14)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• "TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations
• An Excess Due to Small Grains Around The Nearby K0V Star HD69830: Asteroid or Cometary Debris?
• FITSH -- a software package for image processing
• "TNOs are Cool": A Survey of the Transneptunian Region IV. Size/albedo characterization of 15 scattered disk and detached objects observed with Herschel Space Observatory-PACS
• Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in η Corvi at ~1 Gyr
• High Resolution HST-STIS Spectra of CI and CO in the Beta Pictoris Circumstellar Disk
• Thermal Properties of Centaurs Asbolus and Chiron
• Albedos of Main-Belt Comets 133P/Elst-Pizarro and 176P/LINEAR
• "TNOs are Cool": A survey of the trans-Neptunian region -- VII. Size and surface characteristics of (90377) Sedna and 2010 EK139
• Cometary activity at 25.7 AU: Hale--Bopp 11 years after perihelion
• Are He and N Abundances in Type I PNe as High as Empirically Derived?
• Frozen to death? -- Detection of comet Hale-Bopp at 30.7 AU

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