.png) Wirtanen at perihelion on 12 December 2018 | |
| Discovery | |
|---|---|
| Discovered by | Carl A. Wirtanen |
| Discovery site | Lick Observatory |
| Discovery date | 17 January 1948 |
| Designations | |
| P/1948 A1, P/1954 R2 | |
| |
| Orbital characteristics[2][3] | |
| Epoch | 13 September 2023 (JD 2460200.5) |
| Observation arc | 75.89 years |
| Number of observations | 7,527 |
| Aphelion | 5.127 AU |
| Perihelion | 1.055 AU |
| Semi-major axis | 3.091 AU |
| Eccentricity | 0.65867 |
| Orbital period | 5.43 years |
| Inclination | 11.749° |
| 82.164° | |
| Argument of periapsis | 356.33° |
| Mean anomaly | 314.77° |
| Last perihelion | 19 May 2024 |
| Next perihelion | 27 October 2029[1] |
| TJupiter | 2.818 |
| EarthMOID | 0.071 AU |
| JupiterMOID | 0.169 AU |
| Physical characteristics[3][6] | |
Mean radius | 0.6 km (0.37 mi)[4] |
| 7.9 hours[5] | |
| Comet total magnitude (M1) | 16.6 |
| Perihelion distance at different epochs[7] | |||||||
| Epoch | Perihelion (AU) | ||||||
|---|---|---|---|---|---|---|---|
| 1967 | 1.61 | ||||||
| 1974 | 1.26 | ||||||
| 1986 | 1.08 | ||||||
| 2013 | 1.05 | ||||||
| 2035 | 1.08 | ||||||
| 2046 | 1.22 | ||||||
| 2059 | 1.98 | ||||||
| 2095 | 2.01 | ||||||
46P/Wirtanen is a smallJupiter-family comet with a currentorbital period of 5.4 years.[8][9] It was the original target for close investigation by theRosettaspacecraft, planned by theEuropean Space Agency, but an inability to meet thelaunch window causedRosetta to be sent to67P/Churyumov–Gerasimenko instead.[10] In December 2019, astronomers reported capturing an outburst of the comet in substantial detail by theTESS observatory.[8][9] It was last observed in 2023 and will next come to perihelion in 2029
46P/Wirtanen was discovered photographically on 17 January 1948, by the American astronomerCarl A. Wirtanen.[11] The plate was exposed on January 15 during a stellar proper motion survey for theLick Observatory. Due to a limited number of initial observations, it took more than a year to recognize this object as a short-period comet.
The July 2013 perihelion passage was not favorable, only reaching a magnitude of 14.7.[12] Between January 23 and September 26 of 2013, the comet had anelongation less than 20 degrees from the Sun.
On 16 December 2018, the comet passed 0.07746 AU (11.6 million km; 7.20 million mi; 30.1 LD) from Earth,[3] marking one of the 10 closest comet flybys of Earth in the last 70 years.[13] The comet reached an estimated magnitude of 3.9,[14] making this pass the brightest one predicted, and the brightest close approach for the next 20 years.[12] The comet experienced six outbursts, with the comet brightening by −0.2 to −1.6 magnitudes.[15]
The 2018 close approach, combined with Wirtanen's brightness provides an opportunity to study a potential future spacecraft mission target in detail. A worldwide observing campaign[16] was organized to capitalize on the favorable circumstances of the 2018 apparition.
The comet was the target for the proposedComet Hopper mission, which reached the finalist stage in the NASADiscovery 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 theInSight mission, a Mars lander. The Comet Hopper was designed to use the ASRG, theAdvanced Stirling Radioisotope Generator.
The Comet Hopper mission, had it been selected, would have had multiple science goals over the 7.3 years of its nominal lifetime. At roughly 4.5 AU (670 million km), 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 within itscoma. 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 approached the Sun, the spacecraft would land and hop multiple times.[18] The final landing would occur at 1.5 AU. As the comet approached the Sun and became more active, the spacecraft would be able to record surface changes.[19]
Also, 46P/Wirtanen was the original destination of theEuropean Space Agency'sRosetta spacecraft mission, but launch 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.[20][21]
Close approaches to Jupiter in 1972 and 1984 moved the comet's orbit closer to Earth, and as ofepoch 2018 the comet has an Earth–MOID of 0.071 AU (10.6 million km).[3] In 2023 Earth passed through a denser part of the 1974meteoroid stream than Earth did in 2007.[22] As a result a shower withradiant in the southern constellation ofSculptor was observed with a zenithal hourly rate (ZHR) of0.65+0.24
−0.20 and was given the nameλ-Sculptorids. The meteors madeatmospheric entry (Ve) at a relatively slow 15 km/s (9.3 mi/s) and as a result the mean mass of the meteoroids observed was about 0.5 grams, about 10 times higher than that of other meteor showers.[23]
| Date | Stream |
|---|---|
| 2007 | 1974 |
| 2018 | 1980 |
| 2023-December-12 10:54 UT | 1974 |
Russian forecaster Mikhail Maslov had predicted that theEarth's orbit would cross Comet Wirtanen's debris stream as many as four 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 ameteor shower would be visible from Earth, but there was speculation that a shower with as many as 30 meteors per hour might occur.[24]
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 ofPisces.[25]
| Numbered comets | ||
|---|---|---|
| Previous 45P/Honda–Mrkos–Pajdušáková | 46P/Wirtanen | Next 47P/Ashbrook–Jackson |
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