96P/Machholz
A sunskirting comet with a possible extrasolar origin.
Comet 96P/Machholz, also called Machholz 1, is a periodic comet that skims close to the Sun. It was discovered on May 12, 1986, by amateur astronomer Donald Machholz, who spotted it from Loma Prieta peak in central California using 130 mm binoculars. On June 6, 1986, it passed 0.404 AU from Earth. Its most recent perihelion occurred on January 31, 2023. The comet is estimated to be about 6.4 km in diameter.
This comet is the parent body of the Kracht and Marsden sungrazer families. It stands out among comets in several ways. Apart from small SOHO comets, its highly eccentric 5.29-year orbit has the smallest perihelion distance of any numbered short-period comet, bringing it much closer to the Sun than Mercury’s orbit. It is also the only known short-period comet with both high orbital inclination and high eccentricity. In 2007, observations showed it to be depleted in both carbon and cyanogen, a chemical makeup nearly unique among comets with known compositions, hinting at a possible origin outside the Solar System.
The orbit of 96P/Machholz corresponds to the Arietids and the Marsden and Kracht comet groups. Its Tisserand parameter with respect to Jupiter is 1.94—comets are usually classed as Jupiter family if that value exceeds 2. Orbital integrations suggest that TJ was above 2 about 2,500 years ago. The comet is currently in a 9:4 orbital resonance with Jupiter. It will not make another close approach to Earth until 2028, passing at 0.3197 AU. It may eventually be ejected from the Solar System.
For the 2028 perihelion, the comet’s closest approach to the Sun will be 0.116 AU. At perihelion, it travels at 122 km/s. It comes closer to the Sun than any numbered comet except 321P/SOHO. Between 1897 and 2102, its perihelion distance gradually drops from 0.17 AU to 0.09 AU. The year 2081 will mark the first perihelion below 0.1 AU.
Machholz 1 entered the view of the Solar and Heliospheric Observatory (SOHO) in 1996, 2002, 2007, 2012, and 2017, seen by the LASCO instrument’s C2 and C3 coronagraphs. During the 2001/2002 passage, it brightened to magnitude −2 and was very impressive in SOHO images. In 2007, it appeared in LASCO C3’s field from April 2 to 6, peaking around magnitude +2 on April 4; its coma was much smaller than the Sun in volume, but forward scattering made it appear significantly brighter.
Quick Facts
- Discoverer
- Donald E. Machholz
- Discovery Site
- Loma Prieta, California
- Discovery Date
- 12 May 1986
- Mpc Name
- P/1986 J2
- Designations
- Machholz 1 · 1986 VII, 1991 XII, 1986e
- Orbit Ref
- jpldata · MPC
- Epoch
- 21 November 2025 (JD 2461000.5)
- Observation Arc
- 38.17 years
- Obs
- 1,559
- Aphelion
- 5.946 AU
- Semimajor
- 3.031 AU
- Eccentricity
- 0.96173
Facts from the source article.
Lore & Background
96P/Machholz last came to perihelion on January 31, 2023. The comet has an estimated diameter of around 6.4 km. It is the parent body of both the Kracht and Marsden sungrazer families. Its orbit corresponds to the Arietids and the Marsden and Kracht comet groups. The Tisserand parameter with respect to Jupiter is 1.94, and comets are generally classified as Jupiter family if TJ > 2; orbital integrations indicate that TJ was greater than 2 about 2500 years ago. It is currently in a 9:4 orbital resonance with Jupiter. It will not make another close approach to Earth until 2028, when it will pass at a distance of 0.3197 AU. It may eventually be ejected from the Solar System.
Machholz 1 entered the field of view of the orbiting Solar and Heliospheric Observatory (SOHO) in 1996, 2002, 2007, 2012, and 2017, where it was seen by the LASCO instrument. During the 2001/2002 passage the comet brightened to magnitude −2. In 2007, it appeared in SOHO's LASCO C3 field of view from April 2 to 6, peaking around magnitude +2. The comet SOHO 2333 is believed to be a fragment of Machholz that came off during the 2007 perihelion. During the 2012 perihelion, two small faint fragments were detected in SOHO C2 images, five hours ahead of the comet, probably fragmented during the 2007 passage. The 2017 perihelion was on October 27, 2017, and the January 31, 2023 perihelion was the sixth passage observed by SOHO.
Reader's Guide
96P/Machholz is significant as the only known short-period comet with both high orbital inclination and high eccentricity. Its chemical composition is nearly unique among comets with known compositions: spectrographic analysis during its 2007 apparition showed it to have far fewer carbon molecules than other comets, with other comets having on average 72 times as much cyanogen. The only two comets previously seen with similar depletion were C/1988 Y1 (Yanaka) and C/2025 K1 (ATLAS), but they have substantially different orbits. Three hypotheses explain this composition: it may be an interstellar comet captured from outside the Solar System; it may have formed in an extremely cold region where most carbon is trapped; or repeated baking by the Sun at perihelion may have stripped most of its cyanogen. The comet's orbit is gradually evolving, with perihelion dropping from 0.17 AU to 0.09 AU between 1897 and 2102; 2081 will be the first perihelion below 0.1 AU. Its legacy includes being the parent body of two sungrazer families and being repeatedly observed by SOHO, with fragments detected during multiple passages.
Did You Know?
- 96P/Machholz was discovered on 12 May 1986 by amateur astronomer Donald Machholz using 130 mm binoculars on Loma Prieta peak in central California.
- In 2007, it was found to be both carbon-depleted and cyanogen-depleted, a composition nearly unique among comets.
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