46P/Wirtanen

46P/Wirtanen

Credit:ESO
Discovery
Discovered by	Carl A. Wirtanen
Discovery date	January 17, 1948
Alternative designations	1961 IV; 1960m; 1967 XIV; 1967k; 1974 XI; 1974i; 1986 VI; 1985q; 1991 XVI; 1991s; 46P/1948 A1; 1947 XIII; 1948b; 46P/1954 R2; 1954 XI; 1954j
Orbital characteristics A
Epoch	September 3, 2002 (JDT 2452520.5)
Aphelion	5.129946 AU
Perihelion	1.0587602 AU
Semi-major axis	3.0943529 AU
Eccentricity	0.6578412
Orbital period	5.44 a
Inclination	11.73813°
Last perihelion	July 9, 2013 February 2, 2008
Next perihelion	2018-Dec-12

46P/Wirtanen is a small short-period comet with a current orbital period of 5.4 years. It was the original target for close investigation by the Rosetta spacecraft, planned by the European Space Agency, but an inability to meet the launch window led to Rosetta being sent to 67P/Churyumov–Gerasimenko instead. It belongs to the Jupiter family of comets, all of which have aphelia between 5 and 6 AU. Its diameter is estimated at 1.2 kilometres (0.75 mi).

Discovery

46P/Wirtanen was discovered photographically on January 17, 1948, by the American astronomer Carl A. Wirtanen. The plate was exposed on January 15 during a stellar proper motion survey for the Lick Observatory. Due to a limited number of initial observations, it took more than a year to recognize this object as a short-period comet.

Perihelion passages

The 2013 perihelion passage was not favorable since between January 23 and September 26, the comet had an elongation less than 20 degrees from the Sun.

On 16 December 2018 the comet will pass 0.0777 AU (11,620,000 km; 7,220,000 mi) (~30 LD) from Earth.

Exploration proposals

Main article: Comet Hopper

The comet was the target for the proposed 2016 Comet Hopper mission, which reached the finalist stage in the Discovery program. It was one of only three missions in that selection to have a more detailed study. The selection process was ultimately won in 2012 by the InSight mission, a Mars lander. The Comet Hopper was designed to use the ASRG, the Advanced Stirling Radioisotope Generator.

The Comet Hopper mission, if it were selected, would have had multiple science goals over the 7.3 years of its nominal lifetime. At roughly 4.5 AU the spacecraft would rendezvous with Comet Wirtanen and begin to map the spatial heterogeneity of surface solids as well as gas and dust emissions from the coma - the nebulous envelope around the nucleus of a comet. The remote mapping would also allow for any nucleus structure, geologic processes, and coma mechanisms to be determined. After arriving at the comet, the spacecraft would approach and land, then subsequently hop to other locations on the comet. As the comet approaches the Sun, the spacecraft would land and hop multiple times. The final landing would occur at 1.5 AU. As the comet approaches the Sun and becomes more active, the spacecraft would be able to record surface changes.

Also, 46P/Wirtanen was the original destination of the European Space Agency's Rosetta spacecraft mission, but delays meant that the comet was no longer easily reachable and another periodic comet, 67P/Churyumov–Gerasimenko, was chosen as the mission's target instead.

Associated Piscid Meteor Shower

Russian forecaster Mikhail Maslov had predicted that the Earth's orbit would cross Comet Wirtanen's debris stream as many as 4 times between December 10 and December 14, 2012. As there had not previously been an encounter with this debris stream, it was not certain whether or not a meteor shower would be visible from Earth, but there was speculation that a shower with as many as 30 meteors per hour might occur.

Observers in Australia reported that on the night of December 14, 2012, as many as a dozen meteors were seen emanating from the predicted radiant in the constellation of Pisces.

External links

• IAU Ephemerides page for 46P
• 46P on JPL Small-Body Database Browser
• 46P/Wirtanen – Seiichi Yoshida @ aerith.net

Periodic comets (by number)
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