C/1999 H1 (Lee)

C/1999 H1 (Lee) is a non-periodic comet observed between April 1999 and January 2000. It is the only comet discovered by Australian astronomer, Steven Lee. Lee found the comet visually during a star party near Mudgee, New South Wales on 16 April 1999.^[4] He estimated the comet had an apparent magnitude of 9.^[1]

C/1999 H1 (Lee)

A mosaic of C/1999 H1 (Lee) taken on 9 December 1999
Discovery[1]
Discovered by	Steven Lee
Discovery site	Mudgee, Australia
Discovery date	16 April 1999
Orbital characteristics[2]
Epoch	17 August 1999 (JD 2451407.5)
Observation arc	267 days
Number of observations	1,019
Aphelion	~5,500 AU
Perihelion	0.708 AU
Semi-major axis	~2,800 AU
Eccentricity	0.99974
Orbital period	~146,000 years
Inclination	149.25°
Longitude of ascending node	162.65°
Argument of periapsis	40.702°
Mean anomaly	0.0002°
Last perihelion	11 July 1999
TJupiter	–0.896
Earth MOID	0.151 AU
Jupiter MOID	0.257 AU
Physical characteristics[2]
Comet total magnitude (M1)	9.4
Comet nuclear magnitude (M2)	13.1
Apparent magnitude	6.0 (1999 apparition)[3]

Physical characteristics

In February 1999, Comet Lee became the first moderately active comet where its properties were observed and measured by the Hubble Space Telescope in ultraviolet light.^[5] Data obtained through the Telescope's STIS revealed the presence of S₂ within its coma, making it the third comet known where such chemical compound was detected after C/1983 H1 (IRAS–Araki–Alcock) and C/1996 B2 (Hyakutake).^[5] Observations of the coma from the La Palma Observatory in June 1999 indicated that the comet was dust-poor, with a relatively high gas-to-dust mass ratio of around 6.5–11.7 and a dust production rate of around Afρ = 500 cm.^[6]

Spectrophotometric observations conducted at the European Southern Observatory between May and October 1999 detected the presence of OH, CH₃OH, HCN, H₂CO, and CS within its coma.^[7] Water production rate while it was at least 1.3–1.7 AU (190–250 million km) from the Sun was estimated to be about 3.2×10²⁸ sec⁻¹ based on observations conducted by the Submillimeter Wave Astronomy Satellite (SWAS) during its outbound trajectory between September and December 1999.^[8]

Additional data obtained from the Keck Observatory in August 1999 revealed that the comet is strongly depleted in carbon monoxide gas compared to other comets like C/1995 O1 (Hale–Bopp) and C/1996 B2 (Hyakutake), which may demonstrate the chemical diversity that occurred during the formation of the outer Solar System.^[9]