Wednesday 16 December 2020

Comet 141P/Machholz 2 reaches Perihelion.

Comet 141P/Machholz 2 reaches its perihelion (the closest point on its orbit to the Sun) on Wednesday 16 December 2020, when it will be approximately 0.81 AU from the Sun (i.e. 81% of the distance between the Earth and the Sun). At this time the comet will be 0.21 AU from the Earth, in the constellation of Aquarius, having a magnitude of 9.74, making visible with a good pair of binoculars or small telescope.

 
Comet 141P/Machholz 2 imaged in Septermber 1996 from Austria. Michael J├Ąger/Cometography.

141P/Machholz 2 was discovered in August 1994 by Donald Machholz of Colfax, California. The designation 141P/ implies that it was the 141st Comet ever discovered, and that it is a periodic comet (P, again, most comets are periodic, but the term 'periodic comet' is reserved for those with periods of less than 200 years, since these can be reliably predicted), while the 2 indicates that it was the second comet discovered by Donald Machholz.

Comet 141P/Machholz 2 has an orbital period of 1918 days (5.25 years) and a highly eccentric orbit tilted at an angle of 12.8° to the plain of the Solar System, that brings it from 0.75 AU from the Sun at closest perihelion (75% of the distance between the Earth and the Sun; although the perihelion distance is variable and the comet does not come this close to the Sun on every orbit);to 5.28 AU from the Sun at aphelion (528 times as far from the Sun as the Earth or slightly inside the orbit of the planet Jupiter). As a comet with a period of less than 20 years with an orbit angled at less than 30° to the plane of the Solar System, 141P/Machholz 2 is considered to be a Jupiter Family Comet.

 
The calculated orbit and position on 16 December 2020 of 141P/Machholz 2.  JPL Small Body Database.

This means that 141P/Machholz 2 has occasional close encounters with the Earth, with the last thought to have happened in January 2000 and the next predicted in December 2036. The asteroidalso has occasional close encounters with the planets Venus, which it is next predicted to pass in February 2079, and Jupiter, which it last came close to in October 2017 and is expected to pass again in January 2030. Objects which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.

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