C/1991 Y1 (Zanotta–Brewington)

Lore & Background

Comet Zanotta–Brewington was discovered independently by Mauro V. Zanotta and Howard J. Brewington, and observed telescopically from December 1991 through May 1992. Photometric studies at La Silla Observatory measured a relatively high gas production rate of 110 × 10^21 molec s−1/cm−1 during perihelion, which decreased with cyanogen activity by March 1992. Its production rate ratio was compared to that of C/1991 X2 (Mueller) while both comets were around 0.64–0.72 AU from the Sun using CCD spectroscopy; their NH2/H2O ratios were identical, but Zanotta–Brewington's CN/H2O ratio was two times less than Mueller's.

In September 1993, Brian G. Marsden calculated an orbit spanning the comet's entire 130-day observation arc. He noted that the comet was weakly hyperbolic during its inbound trajectory, indicating it was a dynamically new comet originating from the Oort cloud. Gravitational perturbations by the giant planets reduced the comet's relative velocity enough to attain a highly eccentric orbit lasting roughly 27,000 years during its outbound trajectory.

Reader's Guide

C/1991 Y1 (Zanotta–Brewington) is significant as a dynamically new comet from the Oort cloud, confirmed by its weakly hyperbolic inbound orbit. Its high gas production rate at perihelion, measured at La Silla Observatory, provides insight into the volatile content of pristine cometary material. The comparison with C/1991 X2 (Mueller) using CCD spectroscopy revealed identical NH2/H2O ratios but a CN/H2O ratio half that of Mueller, suggesting compositional differences among Oort cloud comets. The orbital calculations by Brian G. Marsden, based on a 130-day observation arc, show that gravitational perturbations by giant planets transformed its trajectory into a highly eccentric orbit with an outbound period of roughly 27,000 years. This comet's legacy lies in its contribution to understanding the chemical diversity and dynamical evolution of comets from the Oort cloud.

Did You Know?

• Its gas production rate at perihelion was 110 × 10^21 molec s−1/cm−1, measured at La Silla Observatory.
• Its CN/H2O ratio was two times less than that of C/1991 X2 (Mueller).
• Brian G. Marsden calculated its orbit in September 1993, finding it weakly hyperbolic inbound.