C/1999 H1 (Lee)

Lore & Background

Comet Lee was discovered visually by Australian amateur astronomer Steven Lee on 16 April 1999 during a star party near Mudgee, New South Wales. He estimated its apparent magnitude at 9. The comet was observed from April 1999 to January 2000. In February 1999, it became the first moderately active comet studied by the Hubble Space Telescope in ultraviolet light using the STIS instrument, which detected S₂ in its coma—only the third comet known to have this compound, after C/1983 H1 (IRAS–Araki–Alcock) and C/1996 B2 (Hyakutake). Observations from the La Palma Observatory in June 1999 showed the comet was dust-poor, with a relatively high gas-to-dust mass ratio of about 6.5–11.7 and a dust production rate of Afρ = 500 cm. Spectrophotometric observations at the European Southern Observatory between May and October 1999 detected OH, CH₃OH, HCN, H₂CO, and CS in its coma. The Submillimeter Wave Astronomy Satellite (SWAS) estimated a water production rate of about 3.2×10²⁸ sec⁻¹ when the comet was 1.3–1.7 AU from the Sun during its outbound trajectory from September to December 1999. Data from the Keck Observatory in August 1999 revealed that Comet Lee is strongly depleted in carbon monoxide gas compared to comets like C/1995 O1 (Hale–Bopp) and C/1996 B2 (Hyakutake), suggesting chemical diversity during the formation of the outer Solar System. The nucleus is estimated to be roughly 12.58 km in diameter.

Reader's Guide

C/1999 H1 (Lee) holds significance as a non-periodic comet that provided early ultraviolet observations of a moderately active comet by the Hubble Space Telescope, marking a milestone in cometary science. Its detection of S₂ made it only the third comet known to contain this compound, highlighting the chemical variety among comets. The comet's dust-poor nature and high gas-to-dust ratio, measured at La Palma Observatory, contrast with many other comets, while its strong depletion in carbon monoxide, observed at Keck Observatory, underscores the chemical diversity that existed during the formation of the outer Solar System. The water production rate estimated by SWAS and the detection of multiple molecules (OH, CH₃OH, HCN, H₂CO, CS) by the European Southern Observatory further characterize its composition. Discovered by a single amateur astronomer, Steven Lee, during a star party, the comet exemplifies the contributions of visual observers to cometary discovery. Its legacy lies in the data it provided on cometary chemistry and physical properties, contributing to the understanding of Solar System formation.

Did You Know?

• C/1999 H1 (Lee) is the only comet discovered by Australian astronomer Steven Lee.
• It was the first moderately active comet observed by the Hubble Space Telescope in ultraviolet light.
• Its nucleus is estimated to be about 12.58 km in diameter.