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96P 20070403 000500 HI1A.png
96P/Machholz as seen by STEREO-A in April 2007
Discovered by Donald Machholz[1]
Discovery date May 12, 1986
96P, Machholz, Machholz 1, 1986 J2, 1991 XII, 1986e, 1986 VII
Orbital characteristics A
Epoch September 6, 2013
(JD 2456541.5)[1]
Aphelion 5.9441 AU
Perihelion 0.12375 AU
Semi-major axis 3.0339 AU
Eccentricity 0.95921
Orbital period 5.28 yr
Inclination 58.312°
Last perihelion July 14, 2012 18:49[2][3][4]
Next perihelion October 27, 2017[4][5]

Comet 96P/Machholz or 96P/Machholz 1[6] is a short-period comet discovered on May 12, 1986, by amateur astronomer Donald Machholz on Loma Prieta peak, in central California using 130 millimetres (5.1 in) binoculars.[6][7] On June 6, 1986, comet 96P/Machholz passed 0.40373 AU (60,397,000 km; 37,529,000 mi) from the Earth.[8] Comet 96P/Machholz last came to perihelion on July 14, 2012,[2] and will next come to perihelion on October 27, 2017.[4] 96P/Machholz has an estimated radius of around 3.2 km (2.0 mi).[9]

Machholz 1 is unusual among comets in several respects. Its highly eccentric 5.2 year orbit has the smallest perihelion distance known among numbered/regular[10] short-period comets, bringing it considerably closer to the Sun than the orbit of Mercury. It is also the only known short-period comet with both high orbital inclination and high eccentricity.[9] In 2007, Machholz 1 was found to be both carbon-depleted and cyanogen-depleted, a chemical composition nearly unique among comets with known compositions.[11][12] The chemical composition implies a different and possible extrasolar origin.[13]


The orbit of Machholz 1 corresponds to the Arietids and the Marsden and Kracht Comet groups.[14] Its Tisserand parameter with respect to Jupiter, TJ, is 1.94 and comets are generally classified as Jupiter family if TJ > 2.[9] Orbital integrations indicate that TJ was greater than 2 about 2500 years ago.[9] Machholz 1 is currently in a 9:4 orbital resonance with Jupiter.[9] 96P will not make another close approach to the Earth until 2028, when it will pass at a distance of 0.31972 AU (47,829,000 km; 29,720,000 mi).[8]


Machholz 1 entered the field of view of the orbiting Solar and Heliospheric Observatory (SOHO) in 1996, 2002, and 2007, where it was seen by the corona-observing LASCO instrument in its C2 and C3 coronagraphs.[6][15] During the 2002 passage the comet brightened to magnitude −2,[16] and was very impressive as seen by SOHO.[17] During the comet's last perihelion passage in 2007, it appeared in SOHO's LASCO C3's field of view from April 2 to 6, peaking in brightness on April 4, 2007,[18] around magnitude +2.[19] In these observations, its coma was substantially smaller than the Sun in volume, but the forward scattering of light made the comet appear significantly brighter.[20]

The most recent opportunity to observe Machholz 1 was when it returned to perihelion in 2012.[13] Between July 12–17, 2012, comet Machholz was visible in the SOHO LASCO/C3 field of view and expected to brighten to about magnitude +2.[21] Two small faint fragments of Comet Machholz were detected in the SOHO C2 images.[22] The fragments were 5 hours ahead of Comet Machholz, and probably fragmented from the comet during the 2007 perihelion passage.[22]

Unusual composition[edit]

Spectrographic analysis of the coma of Machholz 1 was made during its 2007 apparition, as part of the Lowell Observatory comet composition long-term observing program.[23] When compared with the measured abundances of five molecular species in the comae of the other 150 comets in their database, these measurements showed Machholz 1 to have far fewer carbon molecules than the 150 other comets.[9] These other comets had on average 72 times as much cyanogen as Machholz 1.

The only comet previously seen with similar depletion both in carbon-chain molecules and cyanogens is Yanaka (1988r; 1988 Y1), but it has a substantially different orbit.[24]

Possible cause of the unusual chemical composition[edit]

There are currently three hypotheses to explain the chemical composition of Machholz 1.

Extrasolar origin[edit]

One hypothesis for the difference is that Machholz 1 was an interstellar comet from outside the Solar System and was captured by the Sun.[25]

Oort cloud origin[edit]

Other possibilities are that it formed in an extremely cold region of the Solar System (such that most carbon gets trapped in other molecules).

Extreme thermal alteration[edit]

Given how close it approaches the Sun at perihelion, repeated baking by the Sun has stripped most of its cyanogen.


  1. ^ a b "JPL Small-Body Database Browser: 96P/Machholz 1" (Epoch: September 6, 2013). Jet Propulsion Laboratory. Retrieved December 6, 2014. 
  2. ^ a b Yoshida, Seiichi (December 30, 2007). "96P/Machholz 1". Aerith.net. Archived from the original on April 27, 2011. Retrieved April 6, 2011. 
  3. ^ Nakano, Syuichi (April 22, 2009). "96P/Machholz 1 (NK 1771)". OAA Computing and Minor Planet Sections. Retrieved February 20, 2012. 
  4. ^ a b c "Observer Table for 96P/Machholz 1". JPL Horizons On-Line Ephemeris System. Retrieved July 16, 2012.  (Observer Location:@sun)
  5. ^ "96P/Machholz Orbit". Minor Planet Center. Retrieved June 17, 2014. 
  6. ^ a b c Kronk, Gary W. "96P/Machholz 1". Cometography. Archived from the original on July 5, 2008. Retrieved August 6, 2008. 
  7. ^ "Don Machholz and Comet 96P". Astronomy.com. March 29, 2007. Retrieved August 6, 2008. 
  8. ^ a b "96P/Machholz 1". JPL Small-Body Database Browser (Epoch: September 6, 2013). Retrieved December 6, 2014. 
  9. ^ a b c d e f Schleicher, David G. (2008). "The Extremely Anomalous Molecular Abundances of Comet 96P/MACHHOLZ 1 from Narrowband Photometry". The Astronomical Journal. 136 (5): 2204–2213. Bibcode:2008AJ....136.2204S. doi:10.1088/0004-6256/136/5/2204. 
  10. ^ A'Hearn, M. F.; Millis, R. L.; Schleicher, D. G.; Osip, D. J.; Birch, P. V. (1995). "The ensemble properties of comets: Results from narrowband photometry of 85 comets, 1976-1992". Icarus. 118 (2): 223–270. Bibcode:1995Icar..118..223A. doi:10.1006/icar.1995.1190.  (login required)
  11. ^ "IAU Circular 8842". International Astronomical Union. June 6, 2007. Retrieved July 5, 2011. 
  12. ^ Langland-Shula, Laura E.; Smith, Graeme H. (2007). "The Unusual Spectrum of Comet 96P/Machholz". The Astrophysical Journal Letters. 664 (2): L119–L122. arXiv:0706.2022Freely accessible. Bibcode:2007ApJ...664L.119L. doi:10.1086/520839. 
  13. ^ a b MacRobert, Alan (December 2, 2008). "A Very Oddball Comet". Sky & Telescope. Retrieved December 5, 2008. 
  14. ^ Katsuhito, Ohtsuka; Nakano, Syuichi; Yohikawa, Makoto (February 2003). "On the Association among Periodic Comet 96P/Machholz, Arietids, the Marsden Comet Group, and the Kracht Comet Group". Publications of the Astronomical Society of Japan. 55 (1): 321–324. Bibcode:2003PASJ...55..321O. doi:10.1093/pasj/55.1.321. 
  15. ^ Boschat, Mike (January 7, 2002). "Comet 96P/Machholz now in the SOHO C3 images". Meteorobs.org. Archived from the original on July 6, 2008. Retrieved August 6, 2008. 
  16. ^ Yoshida, Seiichi (May 29, 2007). "96P/Machholz 1 (2002)". Aerith.net. Retrieved February 3, 2012. 
  17. ^ "Exclusive Views of Comet 96P/Machholz". Solar and Heliospheric Observatory. NASA. January 6–10, 2002. Retrieved February 3, 2012. 
  18. ^ SOHO Movie Theater
  19. ^ Yoshida, Seiichi (September 20, 2007). "96P/Machholz 1 (2007)". Aerith.net. Archived from the original on August 29, 2008. Retrieved August 6, 2008. 
  20. ^ Marcus, Joseph C. (April 2007). "Forward-Scattering Enhancement of Comet Brightness. I. Background and Model". International Comet Quarterly. 29 (2): 39–66. Bibcode:2007ICQ....29...39M. 
  21. ^ Kusiak, Michal. "Transits of Objects through the LASCO/C3 field of view (FOV) in 2012". Sungrazer Project. United States Navy. Retrieved February 1, 2012. 
  22. ^ a b Battams, Karl (July 16, 2012). "Breaking News: Comet Machholz had babies!!". Sungrazer Project. United States Navy. Retrieved July 16, 2012. 
  23. ^ "A New Compositional Class of Comets: from Fire, Ice, or Beyond? Lowell Observatory Astronomer Confirms New Class of Comets" (Press release). Lowell Observatory. December 2, 2008. Retrieved December 5, 2008. 
  24. ^ Fink, Uwe (September 1992). "Comet Yanaka (1988r): A New Class of Carbon-Poor Comet". Science. 257 (5078): 1926–9. Bibcode:1992Sci...257.1926F. doi:10.1126/science.257.5078.1926. PMID 17753496. 
  25. ^ Bryner, Jeanna (December 2, 2008). "Odd Comet Possibly from Another Star System". Space.com. 

External links[edit]

Numbered comets
96P/Machholz Next