6P/d'Arrest
Periodic comet discovered by Heinrich Ludwig d'Arrest in 1851.
6P/d'Arrest, also called d'Arrest's Comet or Comet d'Arrest, is a periodic comet that orbits the Sun between Mars and Jupiter every 6.54 years. Heinrich Ludwig d'Arrest, a German astronomer, discovered it as the second of three comets he found. Its next perihelion—the closest point to the Sun—occurs on March 31, 2028, at a distance of 1.35 AU, when it should reach an apparent magnitude of about 11.
The comet was first spotted by d'Arrest in Leipzig, Germany, from June 28 to 30, 1851. In 1991, two independent research teams—Andrea Carusi and Giovanni B. Valsecchi in Rome, along with Ľubor Kresák and Margita Kresáková in Bratislava—proposed that this comet is the same one observed earlier by Philippe de La Hire in 1678. On August 12, 1976, it passed within 0.151 AU (22.6 million km) of Earth. Its 2015 appearance was poor because its solar elongation stayed below 30 degrees from October 2014 through May 2015. The most recent perihelion was on September 17, 2021, when the comet had a solar elongation of 95 degrees and shone at roughly magnitude 10.
During its 2008 return, infrared spectroscopy at the Keck Observatory detected water (H₂O), methanol (CH₃OH), ethane (C₂H₆), formaldehyde (H₂CO), and ammonia (NH₃) in its coma; the last three gases were relatively depleted compared to other comets. The nucleus is estimated to be 3.2 km in diameter. Photometric measurements in 1976 gave a rotation period of about 5.17 ± 0.01 hours, but a 2003 periodogram analysis of its lightcurve revised this to a longer period of 6.67 ± 0.03 hours.
A 1966 study proposed a Mariner-type mission to 6P/d'Arrest, to be launched from an Atlas-Centaur by April 1976 and arriving at a distance of 100,000 km about 115–145 days later, but it was never carried out. The comet was one of three targets—alongside 2P/Encke and 73P/Schwassmann–Wachmann—for the CONTOUR mission, which launched in 2002 but lost contact soon after reaching orbit. Had it succeeded, CONTOUR would have flown by d'Arrest in 2008 after visiting two other comets. Around 2007, 6P/d'Arrest was among nine comets studied for a preliminary sample return mission.
Quick Facts
- Discoverer
- Heinrich Louis d'Arrest
- Discovery Site
- Leipzig, Germany
- Discovery Date
- June 28, 1851
- Mpc Name
- C/1678 R1, P/1851 M1 · P/1857 X1
- Orbit Ref
- jpl1 · MPC
- Epoch
- 25 February 2023 (JD 2460000.5)
- Observation Arc
- 344 years
- Earliest Precovery Date
- September 11, 1678Carusi_1991
- Obs
- 3,732
- Perihelion
- 1.353 AU
- Aphelion
- 5.639 AU
- Semimajor
- 3.497 AU
Facts from the source article.
Lore & Background
6P/d'Arrest was first observed by Heinrich Ludwig d'Arrest in Leipzig, Germany, between June 28–30, 1851. In 1991, a study by Andrea Carusi and Giovanni B. Valsecchi, alongside Ľubor Kresák and Margita Kresáková, independently suggested that this comet is the same as one previously observed by Philippe de La Hire in 1678. The comet passed within 0.151 AU from Earth on August 12, 1976. Its apparition in 2015 was unfavorable due to a solar elongation of less than 30 degrees from October 2014 until May 2015. 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 10.
During its 2008 apparition, infrared spectroscopy at the Keck Observatory detected emissions of H2O, CH3OH, C2H6, H2CO, and NH3 from its coma, with the latter three gases relatively depleted compared to other comets. The comet nucleus is estimated at 3.2 km in diameter. Photometric measurements in 1976 revealed a rotation period of around 5.17±0.01 hours, but a periodogram analysis in 2003 suggested a longer rotation period of about 6.67±0.03 hours.
A 1966 study proposed a Mariner-type mission to 6P/d'Arrest planned for launch by April 1976, but this did not come to fruition. The comet was one of a trio targeted by the ill-fated CONTOUR mission, which lost contact after launch in 2002; had it been functional, a flyby of d'Arrest would have occurred in 2008. Around 2007, it was one of nine comets examined for a preliminary sample return mission study, and later three surface sample return missions (CONDOR, CORSAIR, and CAESAR) were finalists for the New Frontiers Program, but 67P/Churyumov–Gerasimenko and 88P/Howell were chosen as targets, and ultimately Dragonfly was selected.
Reader's Guide
6P/d'Arrest holds significance as a well-observed periodic comet with a relatively short orbital period of 6.54 years, allowing frequent returns and study. Its discovery by Heinrich Ludwig d'Arrest in 1851 marks it as the second of three comets he found. The comet's possible identification with an earlier observation from 1678 by Philippe de La Hire, suggested independently by two research teams in 1991, adds historical depth to its record. Physical studies, including infrared spectroscopy at Keck Observatory in 2008, have characterized its coma composition, revealing depletion of certain gases relative to other comets. The comet's nucleus, estimated at 3.2 km in diameter, has had its rotation period debated, with measurements from 1976 and 2003 yielding different values. 6P/d'Arrest was considered for multiple space missions, including a proposed Mariner-type flyby in the 1970s, the CONTOUR mission (which failed after launch), and as a candidate for comet sample return studies in the 2000s and 2010s. Though no mission has yet visited it, these proposals underscore its perceived scientific value. Its next perihelion in March 2028 at magnitude 11 will offer another opportunity for observation.
Did You Know?
- A 1991 study suggested this comet may be the same as one observed by Philippe de La Hire in 1678.
- The comet passed within 0.151 AU of Earth on August 12, 1976.
More in Named Comets, Part 5 1-24
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