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]
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.[2][11]
The comet passed within 0.151 AU (22.6 million km; 14.0 million mi) from Earth on August 12, 1976.[5] 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.[5] 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]
^ abA. Carusi; G. B. Valesecchi; L. Kresak; M. Kresakova (1991). "Observations of Periodic Comet d'Arrest in 1678 and implications for its evolutionary history". Astronomy & Astrophysics. 252 (1): 377–384. Bibcode:1991A&A...252..377C. ISSN0004-6361. S2CID118960268.
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