Comet C/Hale-Bopp

1. Comet C/Hale-Bopp Christina O. Lee Astro 249 Comet Hale-Bopp

2. Discovery of C/Hale-Bopp • Discovered in 1995 by Alan Hale (professional astronomer in New Mexico, left figure) and Thomas Bopp (amateur astronomer in Arizona) • Both were observing at their home locations on the evening of July 22nd-23rd, 1995 with their amateur telescopes • Hale-Bopp located at 7.15 AU, just outside the Jupiter orbit! Alan Hale Comet Hale-Bopp

3. “C” for Long Period • ~ 4200 yrs ago since last appearance…~2380 yrs for next appearance • Closest approach: • Earth: March 27, 1997 @ 1.315 AU • Sun: April 1, 1997 @ 0.914 AU Comet Hale-Bopp

4. Some Properties of the Nucleus • Known from measurements: • R  30 km (2nd largest comet!) • Spin Period  11.5 • Obliquity  86 degrees • Unknown, but guess: • Density  700 kg m-3 • Specific heat  1400 J kg-1 K-1 • Bond Albedo  0.04 • Emissivity  0.9 Top: Blue filter image. Bottom: false color version. Image credit: http://www2.jpl.nasa.gov/comet/ampo145.html Comet Hale-Bopp

5. Orbital Parameters Strong obliquity of spin axis produces pronounced seasonal effects on C/Hale-Bopp! Image credit: E. Kuhrt, 1999 Comet Hale-Bopp

6. Not two but three tails • Ion tail (H20+), dust tail, and atomic sodium tail • Na tail gets brighter with increasing distance from the nucleus whereas ion/dust tails decrease in brightness • Likely explanation: Extended Na sources operate down the dust tail Image credit: Wilson et al., 1998 Comet Hale-Bopp

7. Striae • System of narrow, nearly rectilinear bands that usually appear in comets < 1 AU from the sun, after perihelion • For Hale-Bopp it was observed BEFORE perihelion at distances > 1AU • Bands do not converge at nucleus and they usually converge at the comet-Sun line on the sunward side • Recurring particle outbursts w/ periodicity of 11h21m from one source of the hale-Bopp nucleus • Particle fragmentation models consider ejection time of parent particles, their acceleration by solar radiation pressure, and time of fragmentation to study the motion of the striae in the dust tail Comet Hale-Bopp

8. Noble gas detection! • A first-ever detection of noble gas found in a comet! • discovered during closest approach (03/27/97) using UV spectra by Stern et. al. (SwRI) • presence/absence of noble gas provides a way of measuring thermal history of comets since noble gases do not interact chemically w/ other elements & they are easily lost from icy bodies at very low temperatures through processes much like evaporation Comet Hale-Bopp

9. Implications from Ar detection • SwRI spectra showed that the Ar abundance was so high that it indicated the comet has always been quite cold and likely formed in the deep outer reaches of the solar system • results indicate that Hale-Bopp was likely formed in the Uranus-Neptune zone (a KBO?), not from the Jupiter zone • High Ar abundance may help explain the unexpected argon abundance found by Galileo Jupiter entry probe • Jupiter seeded with extra argon by the impact of many comets like Hale-Bopp (?) Comet Hale-Bopp

10. References Wealth of Hale-Bopp information and cool pictures at: http://www2.jpl.nasa.gov/comet/ http://encke.jpl.nasa.gov/hale_bopp_info.html E. Kuhrt, H20 Activity of Comet Hale-Bopp, Space Sci. Rev., 90, 75, 1999. Pittichova, J., Z. Sekanina, K. Birkle, H. Boehnhardt, D. Engels, P. Keller, An early investigation of the striated tail of comet Hale-Bopp, EP and S, 78, 329, 1997. Wilson, J. K., J. Baumgardner, and M. Mendillo, Three Tails of comet Hale-Bopp, GRL, 25, 225, 1998. Comet Hale-Bopp