C/1985 R1 (Hartley–Good)

For other comets discovered by Malcolm Hartley, see Comet Hartley.

Comet Hartley–Good, formally designated as C/1985 R1, is a non-periodic comet that was observed from September 1985 to March 1986.^[6] It is the sixth comet discovered overall by Malcolm Hartley and the only one for A. R. Good.^[1]

C/1985 R1 (Hartley–Good)

Discovery[1]
Discovered by	Malcolm Hartley A. R. Good
Discovery site	Siding Spring Observatory
Discovery date	11 September 1985
Designations
Alternative designations	1985 XVII, 1985l[2]
Orbital characteristics[3]
Epoch	2 November 1985 (JD 2446371.5)
Observation arc	187 days
Earliest precovery date	21 August 1985
Number of observations	165
Aphelion	~12,300 AU
Perihelion	0.695 AU
Semi-major axis	~6,160 AU
Eccentricity	0.99989
Orbital period	~480,000 years
Inclination	79.929°
Longitude of ascending node	358.39°
Argument of periapsis	87.033°
Mean anomaly	359.99°
Last perihelion	9 December 1985
TJupiter	0.182
Earth MOID	0.221 AU
Jupiter MOID	2.966 AU
Physical characteristics[4][5]
Mean radius	0.88±0.05 km
Mass	1.10×1012 kg
Mean density	490±70 kg/m3
Comet total magnitude (M1)	8.3
Apparent magnitude	6.3–6.6 (1985 apparition)[6]

Physical characteristics

Ground observations from the comet reveal the presence of organic molecules like CN, CH, C
₂ and C
₃ within its coma.^[7][8] In comparison to comets like 21P/Giacobini–Zinner, the dust-to-gas production ratio for Hartley–Good is relatively low, noting that its dust production is inversely proportional to its distance from the Sun.^[9]

Narrow-band photometry measurements reveal that the nucleus of Hartley–Good has an effective radius of roughly 1.7 km (1.1 mi),^[10] however this was later revised to 0.88±0.05 km.^[4][5] Recorded light-curve data from the comet suggests that water ice from its surface had started to sublimate at a distance of 2.8 AU (420 million km) from the Sun, while also remaining active throughout its most recent apparition.^[11]