Comet 74P/Smirnova-Chernykh reaches perihelion.

Comet 74P/Smirnova-Chernykh will reach its perihelion (the closest point on its orbit to the Sun) on Friday 26 January 2018, when it will be approximately 3.56 AU from the Sun (i.e. 356% of the distance between the Earth and the Sun, between the orbits of Mars and Jupiter), not be particularly close to us. The comet will be in the constellation of Virgo seen from the Earth, though it will not be naked eye visible.

 

 Image of 74P/Smirnova-Chernykh taken from the Kyiv Comet Station in Ukraine on 29 September 2014. 480 second exposure. Comet is faint object at centre of image indicated by lines. Line crossing image is a satelite. Alexander Baransky/Fachgruppe Kometen in der VdS.

74P/Smirnova-Chernykh was discovered in March 1975 Tamara Mikhaylovna Smirnova of the Institute of Theoretical Astronomy in Leningrad in an image made in 1967 by Nikolai Stepanovich Chernykh of the Crimean Astrophysical Observatory. The designation 74/P implies that it is a Periodic Comet (comet with an orbital period of less than 200 years), and that it was the 74th such body discovered.

The orbit of 74P/Smirnova-Chernykh. In The Sky.

74P/Smirnova-Chernykh s a short period, Jupiter Family comet (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), with a 8.52 year orbital period and an elliptical orbit tilted at 6.64° to the plane of the Solar System, which takes it from 3.56 AU from the Sun to 4.78 AU from the Sun (i.e. 4.78 times the average distance between the Earth and the Sun, slightly inside the orbit of Jupiter). 74P/Smirnova-Chernykh is locked into a 3:2 orbital resonance with the planet Jupiter (i.e. completes 3 orbits for every 2 orbits completed by Jupiter), as such it is also considered to be a Quasi-Hilda Object, 

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The nature and origin of the July 2009 Jovian Impactor.

In 2009 the remains of the comet Shoemaker-Levy 9 were observed impacting the Jovian atmosphere, the first time a body had been directly observed colliding with a planet other than the  Earth, and the first time a comet had ever been seen impacting a planet. At the time this was thought to be an extremely rare event, possibly happening as infrequently as once every 500 years. However in July 2009 a scar similar to that caused by the Shoemaker-Levy 9 impact was observed in the southern hemisphere of Jupiter, suggesting that a similar impact had occurred once again.

In a paper published in the Astrophysics Journal Letters on 12 May 2010 and on the arXiv database at Cornell University Library on 13 May 2010, a team of scientists led by Augustin Sánchez-Lavega of the Universidad del País Vasco in Bilbao discuss the July 2009 Jovian impact, and try to determine the nature and origin of the impactor.

Composite image of Jupiter, with the impact scar as seen at the times indicated at beside the boxes; note this is one scar seen at different times in different positions, not a series of scars as seen with the Shoemaker-Levy impact. Sánchez-Lavega et al. (2010).

The impact scar was first detected at 1.02 am GMT on 20 July 2009, as a dark spot as it rotated into view from the west. The most recent previous image of the same spot was taken at 7.40 am GMT on 19 July 2009, constraining the time of the event that caused it to a 17 hour 22 minute window. Images taken by NASA’s Infrared Telescope Facility at 10.13 am GMT on 20 July 2009 showed a bright spot in the methane and hydrogen absorption bands, reaching high above the surrounding clouds; this was the same pattern observed after the Shoemaker-Levy 9 impacts, suggesting this was another impact of a similar nature.

The July 2009 impact scar seen (a) in visible wavelengths, and (b) in infrared. Sánchez-Lavega et al. (2010)

The scar extended 4800 km east-west and 200 km north-south, though it was tilted at 12˚ to true latitude. This is more elongate than the Shoemaker-Levy 9 scars, which Sánchez-Lavega et al. interpret as a sign that the impacting body had a shallower incidence angle relative to the horizon. A thin debris crescent extended 4800 km northwest of the western edge of the scar; a similar crescent structure was seen after the Shoemaker-Levy 9 impacts, and was interpreted as being the result of Coriolis force on the falling material plus a sliding in the atmosphere that conserves the tangential velocity. 

Working from the size of the impact scar, Sánchez-Lavega et al. calculate the original body to have been between 500 m and 1 km in diameter, and that it struck Jupiter at a speed of between 54.52 and 55.1 kms¯¹. Attempts to model the previous path of the impactor prior to the collision by working backwards from the impact site suggest there was a 47% chance that the body was on its original, Sun orbiting path when it hit Jupiter, and a 53% chance that it had previously been captured by the planet into  a Jovicentric orbit, probably more recently than 1989, as was the case with Shoemaker-Levy 9. Furthermore the previous orbit of the body was equally likely to have been a Main Asteroid Belt body (either a Hilda Group Asteroid or a Quasi-Hilda Comet), or a Jupiter Family Comet. Shoemaker-Levy 9 is thought to have originally been a Quasi-Hilda Comet.

See also…

 Ripples in the rings of Jupiter.

 The nature of the Chicxulub impactor.

 The breakup of Main Belt object P/2013 R3 (Catalina-Pan STARRS).

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The nature and history of 'Quasi-Hilda Object' 2000 YN30.

The Asteroid 2000 YN30 was discovered by the Near Earth Asteroid Tracking (NEAT) group in December 2000 (the name 2000 YN30 implies the 763rd asteroid discovered during the second half of December 2000 - period 2000 Y). It is a 1.7 km diameter object in a Hilda Group orbit, in a 2:3 orbital ration with Jupiter. Hilda Group Asteroids complete three orbits for every two orbits of Jupiter, with their aphelion (the furthest point in their orbit from the Sun) moving in succession through the L₄, L₅ Lagrangian points (60º ahead and behind Jupiter) and the opposite point on its orbit (180º ahead and behind). 2000 YN30 does not appear to be in a stable orbit, and is therefore referred to as a 'Quasi-Hilda Object'.

The motion of the Hilda Group Asteroids. Even though each asteroid is in an elliptical orbit, the resonance of their aphelions with the Lagrangian points of Jupiter makes gives the group an apparent triangular shape. Cosmographica.

In a paper published on the online arXiv database at Cornell University Library on 6 May 2013, Yu-Chi Cheng of the Institute of Astronomy at National Central University in Taiwan and and Wing-Huen Ip, also of the Institute of Astronomy, as well as the Institute of Space Science, also at National Central University and the Space Science Institute at Macau University of Science and Technology, discuss the results of a study of 2000 YN30 as it passed through perihelion (the closest point on it's orbit to the Sun) in January 2009 using the LOT One Meter Telescope at Lulin Observatory in Taiwan.

Cheng & Ip detected a dust tail emerging from 2000 YN30 in January 2009, which they were able to track through till March of the same year. Such dust tails typically form as a comet approaches its perihelion, when ice at the surface sublimates away (turns directly from a solid to a gas - liquids do not form in a vacuum), releasing particles of silica trapped in the ice. For this reason they conclude that 2000 YN30 should be considered to be a Jupiter Family Comet (a comet with an orbital period of less than 20 years; in this case 2842 days, or 7.78 years), and rename it 212P/NEAT (2000 YN30), a designation which indicates it is the 212nd periodic comet discovered, that it was discovered by NEAT and that it was formerly known as asteroid 2000 YN30.

The orbit of 212P/NEAT (2000 YN30) and its position around perihelion in January 2009. JPL Small Body Database Browser.

Cheng & Ip next attempted to model the history of 212P/NEAT (2000 YN30)'s orbit, in order to determine how it reached its current trajectory. They conclude that in the most likely history of events, 212P/NEAT (2000 YN30) was captured into a short-period orbit (an orbit taking less than 20 years) by a close encounter with Jupiter around 46 800 years ago, when it reached 0.0063 AU from Jupiter (i.e. 0.63 of the distance between the Earth and the Sun, about 942 500 km), and that a second close encounter with Jupiter, around 18 250 years ago, when it reached 0.021 AU (3 142 000 km) from the planet, moved it into a quasi-Hilda orbit. As noted previously, quasi-Hilda orbits are not stable, and this orbit is calculated to have grown in eccentricity until it achieved a perihelion distance of around 0.8 AU from the Sun (i.e. 80% of the distance between the Earth and the Su, inside the orbit of Earth, but still outside that of Venus). This degree of eccentricity would have been maintained for about 250 years, since when 212P/NEAT (2000 YN30) has been moving steadily towards a more stable Hilda type orbit, something that Cheng & Ip calculate it will continue to do for the foreseeable future.

See also The dust tail of 3200 Phaethon, The perihelion of Comet 103P/Hartley 2, The ejecta of Main-Belt Comet P/2012 T1 (PANSTARRS), The Main-Belt Comet P/2012 T1 (PANSTARRS) and The dust-tail of Asteroid P/2010 A2.

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