Earth, Moon, and Planets

, Volume 77, Issue 3, pp 155–163 | Cite as

Detection of a Satellite Orbiting The Nucleus of Comet Hale–Bopp (C/1995 O1)

  • Z. Sekanina


This paper reports on the detection of a satellite around the principal nucleus of comet Hale-Bopp. As shown elsewhere, a successful morphological model for the comet's dust coma necessitates the postulation of overlapping jet activity from a comet pair. The satellite has been detected digitally on images taken with the Hubble Space Telescope's Wide Field Planetary Camera 2 in the planetary mode on five days in May–October 1996. An average satellite-to-primary signal ratio is 0.21 ± 0.03, which implies that the satellite is ∼30 km in diameter, assuming the main nucleus is ∼70 km across. To avoid collision, the separation distance must exceed 50–60 km at all times. The satellite's projected distances on the images vary from 160 to 210 km, or 0.06 to 0.10 arcsec. The satellite was not detected in October 1995, presumably because of its subpixel separation from the primary. The radius of the gravitational sphere of action of the principal nucleus 70 km in diameter is 370–540 km at perihelion, increasing linearly with the Sun's distance: the satellite appears to be in a fairly stable orbit. Its orbital period at ∼180 km is expected to be ∼2–3 days, much shorter than the intervals between the HST observations. If the main nucleus should be no more than 42 km across, Weaver et al.'s upper limit, the satellite's orbit could become unstable, with the object drifting away from the main nucleus after perihelion. Potentially relevant ground-based detections of close companions are reported. Efforts to determine the satellite's orbit and the total mass of the system will get under way in the near future.

Comet Hale-Bopp  orbiting satellite  nuclear size  sphere of action 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Boehnhardt, H., Birkle, K., Colas, F., Fiedler, A., Jorda, L., Peschke, S., Rauer, H., Schulz, R., Schwehm, G., Thomas, N., Tozzi, G., and West, R. M.: 1997–1999, Earth, Moon, and Planets 78, in press.Google Scholar
  2. Marchis, F., Boehnhardt, H., Hainaut, O., and Le Mignant, D.: 1999, Astron. Astrophys., in press.Google Scholar
  3. Rigaut, F. and Beuzit, J.-L.: 1997, Electronic report updated on March 11, 1997 (URL Scholar
  4. Sekanina, Z.: 1995, Astron. Astrophys. 304, 296–316.ADSGoogle Scholar
  5. Sekanina, Z.: 1997–1999, this issue.Google Scholar
  6. Sekanina, Z.: 1998, Astrophys. J. 509, L133–L136.CrossRefADSGoogle Scholar
  7. Vasundhara, R. and Chakraborty, P.: 1999, Icarus, in press.Google Scholar
  8. Weaver, H. A., Feldman, P. D., A'Hearn, M. F., Arpigny, C., Brandt, J. C., Festou, M. C., Haken, M., McPhate, J. B., Stern, S. A., and Tozzi, G. P.: 1997, Science 275, 1900–1904.CrossRefADSGoogle Scholar
  9. Weaver, H. A. and Lamy, P. L.: 1997–1999, Earth, Moon, and Planets 79, in press.Google Scholar

Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • Z. Sekanina
    • 1
  1. 1.Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaUSA

Personalised recommendations