96P/Machholz

96P/Machholz

96P/Machholz as seen by STEREO-A in April 2007
Discovery
Discovered by Donald Machholz[1]
Discovery date May 12, 1986
Alternative
designations		 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 sungrazing 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 diameter of around 6.4 km (4.0 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]

Orbit

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]

Observations

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

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

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

Extrasolar origin

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

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

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

References

  1. 1 2 "JPL Small-Body Database Browser: 96P/Machholz 1" (Epoch: September 6, 2013). Jet Propulsion Laboratory. Retrieved December 6, 2014.
  2. 1 2 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. 1 2 3 "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. 1 2 3 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. 1 2 "96P/Machholz 1". JPL Small-Body Database Browser (Epoch: September 6, 2013). Retrieved December 6, 2014.
  9. 1 2 3 4 5 6 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. Bibcode:2007ApJ...664L.119L. arXiv:0706.2022 Freely accessible. doi:10.1086/520839.
  13. 1 2 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. 1 2 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. PMID 17753496. doi:10.1126/science.257.5078.1926.
  25. ↑ Bryner, Jeanna (December 2, 2008). "Odd Comet Possibly from Another Star System". Space.com.
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