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C/1985 R1 (Hartley–Good)

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For other comets discovered by Malcolm Hartley, see Comet Hartley.
C/1985 R1 (Hartley–Good)
Discovery[1]
Discovered byMalcolm Hartley
A. R. Good
Discovery siteSiding Spring Observatory
Discovery date11 September 1985
Designations
1985 XVII, 1985l[2]
Orbital characteristics[3]
Epoch2 November 1985 (JD 2446371.5)
Observation arc187 days
Earliest precovery date21 August 1985
Number of
observations		165
Aphelion~12,300 AU
Perihelion0.695 AU
Semi-major axis~6,160 AU
Eccentricity0.99989
Orbital period~480,000 years
Inclination79.929°
358.39°
Argument of
periapsis		87.033°
Mean anomaly359.99°
Last perihelion9 December 1985
TJupiter0.182
Earth MOID0.221 AU
Jupiter MOID2.966 AU
Physical characteristics[5][6]
Mean radius
0.88±0.05 km
Mass1.10×1012 kg
Mean density
490±70 kg/m3
Comet total
magnitude (M1)		8.3
6.3–6.6
(1985 apparition)[4]

Comet Hartley–Good, formally designated as C/1985 R1, is a non-periodic comet that was observed from September 1985 to March 1986.[4] It is the sixth comet discovered overall by Malcolm Hartley and the only one for A. R. Good.[1]

Physical characteristics

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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.[5][6] 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]

References

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  1. ^ a b M. Hartley; A. R. Good (13 September 1985). B. G. Marsden (ed.). "Comet Hartley–Good (1985l)". IAU Circular. 4107 (1).
  2. ^ "Comet Names and Designations". International Comet Quarterly. Retrieved 26 June 2025.
  3. ^ "C/1985 R1 (Hartley–Good) – JPL Small-Body Database Lookup". ssd.jpl.nasa.gov. Jet Propulsion Laboratory. Retrieved 26 June 2025.
  4. ^ a b G. W. Kronk; M. Meyer; D. A. J. Seargent (2017). Cometography: A Catalog of Comets. Vol. 6: 1983–1993. Cambridge University Press. pp. 160–165. ISBN 978-0-521-87216-4.
  5. ^ a b M. L. Paradowski (2022). "A New Indirect Method of Determining Density of Cometary Nuclei" (PDF). Acta Astronomica. 72 (2): 141–159. Bibcode:2022AcA....72..141P. doi:10.32023/0001-5237/72.2.4. ISSN 0001-5237.
  6. ^ a b A. Sosa; J. A. Fernández (2011). "Masses of long-period comets derived from non-gravitational effects". Monthly Notices of the Royal Astronomical Society. 416 (1): 767–782. Bibcode:2011MNRAS.416..767S. doi:10.1111/j.1365-2966.2011.19111.x.
  7. ^ B. S. Rautela; P. S. Goraya; B. B. Sanwal; S. K. Gupta (1989). "Spectrophotometry of comet Hartley–Good (1985l)" (PDF). Earth, Moon, and Planets. 44 (3): 233–242. Bibcode:1989EM&P...44..233R. doi:10.1007/BF00054239.
  8. ^ P. D. Singh; W. F. Huebner; R. D. D. Costa; S. J. C. Landaberry; J. A. de Freitas Pacheco (1997). "Gas and dust release rates and color of dust in comets P/Halley (1986 III), P/Giacobini–Zinner (1985 XIII), and P/Hartley–Good (1985 XVII)". Planetary and Space Science. 45 (4): 455–467. Bibcode:1997P&SS...45..455S. doi:10.1016/S0032-0633(96)00123-7.
  9. ^ S. J. C. Landaberry; P. D. Singh; J. A. de Freitas Pacheco (1991). "Ground-based observations of Comets Giacobini–Zinner (1984e) and Hartley–Good (1985l)". Astronomy & Astrophysics. 246 (2): 597–602. Bibcode:1991A&A...246..597L. ISSN 0004-6361.
  10. ^ K. I. Churyumov; V. K. Rosenbush (1991). "Peculiarities of gas and dust production rates in comets P/Halley (1986 III), P/Giacobini–Zinner (1985 XIII), P/Hartley–Good (1985 XVII) and P/Thiele (1985 XIX)". Astronomische Nachrichten. 312 (6): 385–391. Bibcode:1991AN....312..385C. doi:10.1002/asna.2113120610. ISSN 0004-6337.
  11. ^ P. S. Goraya (1988). "Update on Comet Hartley–Good's light curve" (PDF). Earth, Moon, and Planets. 41 (3): 253–255. Bibcode:1988EM&P...41..253G. doi:10.1007/BF00113987.
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