6P/d'Arrest

6P/d'Arrest (also known as d'Arrest's Comet or Comet d'Arrest) is a periodic comet orbiting between Mars and Jupiter once every 6.54 years. It is the second of three comets discovered by German astronomer, Heinrich Ludwig d'Arrest.^[a]

6P/d'Arrest

Comet d'Arrest photographed by the Zwicky Transient Facility on 21 September 2021
Discovery
Discovered by	Heinrich Louis d'Arrest
Discovery site	Leipzig, Germany
Discovery date	June 28, 1851
Designations
MPC designation	C/1678 R1, P/1851 M1 P/1857 X1
Alternative designations	1910c, 1923b, 1950a 1963f, 1970d, 1976e 1982e, 1987k[1]
Orbital characteristics[2][3]
Epoch	25 February 2023 (JD 2460000.5)
Observation arc	344 years
Earliest precovery date	September 11, 1678[4]
Number of observations	3,732
Aphelion	5.639 AU
Perihelion	1.353 AU
Semi-major axis	3.497 AU
Eccentricity	0.61247
Orbital period	6.539 years
Inclination	19.511°
Longitude of ascending node	138.94°
Argument of periapsis	178.09°
Mean anomaly	79.175°
Last perihelion	September 17, 2021
Next perihelion	March 31, 2028[5][6]
TJupiter	2.709
Earth MOID	0.343 AU
Jupiter MOID	0.208 AU
Physical characteristics[2][7]
Mean diameter	3.2 km (2.0 mi)
Synodic rotation period	6.67±0.03 hours
Comet total magnitude (M1)	15.9

Observational history

It was first observed by Heinrich Ludwig d'Arrest, in Leipzig, Germany, between June 28–30, 1851.^[10] In 1991, a study conducted by Andrea Carusi and Giovanni B. Valsecchi (Istituto Astrofisica Spaziale, Rome), alongside Ľubor Kresák and Margita Kresáková (Slovak Astronomical Institute, Bratislava) independently suggested that this comet is the same as the comet previously observed by Philippe de La Hire in 1678.^[4][11]

The comet passed within 0.151 AU (22.6 million km; 14.0 million mi) from Earth on August 12, 1976.^[2] Its apparition in 2015 was unfavorable as it had a solar elongation of less than 30 degrees from October 2014 until May 2015.^[12] The most recent perihelion passage took place on September 17, 2021, when the comet had a solar elongation of 95 degrees at approximately apparent magnitude of 10.^[13]

Physical characteristics

Guring its 2008 apparition, infrared spectroscopy conducted at the Keck Observatory has detected emissions of H
₂O, CH
₃OH, C
₂H
₆, H
₂CO and NH
₃ from its coma, where the latter three gases were found to be relatively depleted compared to other comets.^[14]

The comet nucleus is estimated at 3.2 km (2.0 mi) in diameter.^[2] Photometric measurements in 1976 revealed a rotation period of around 5.17±0.01 hours,^[15] however this was revised after a periodogram analysis of its lightcurve in 2003 suggests that the comet has a longer rotation period, around 6.67±0.03 hours.^[7]

Exploration

Long-exposure image of Comet d'Arrest taken by Elizabeth Roemer on 7 May 1970

A study in 1966 proposed a Mariner-type mission to 6P/d'Arrest planned to be launched from an Atlas-Centaur by April 1976, arriving at the comet at a distance of 100,000 km (62,000 mi) about 115–145 days after launch, however this did not come to fruition.^[16][17]

6P/d was one of a trio of comets alongside 2P/Encke and 73P/Schwassmann–Wachmann targeted by the ill-fated CONTOUR mission,^[18] which was launched but lost contact soon after reaching orbit in 2002. Had it been functional, the planned date for CONTOUR's flyby of d'Arrest would have been 2008, after visiting two other comets.^[19]

Around 2007, 6P/d was one of nine comets examined for a preliminary comet sample return mission study.^[20] By the 2010s, three comet surface sample return missions (CONDOR, CORSAIR, and CAESAR) were selected as finalists for the New Frontiers Program, but the recently studied 67P/Churyumov–Gerasimenko and 88P/Howell were chosen as the selected targets. These proposals were ultimately not selected in favor of the Dragonfly mission to Titan.

See also

• List of missions to comets