C/2011 L4 (PanSTARRS)

Observational history

Comet C/2011 L4 was still 7.9 AU from the Sun with an apparent magnitude of 19 when it was discovered in June 2011. By early May 2012, it had brightened to magnitude 13.5, and could be seen visually when using a large amateur telescope from a dark site. In October 2012, the coma (expanding tenuous dust atmosphere) was estimated to be about 120000 km in diameter. C/2011 L4 was spotted without optical aid on 7 February 2013 at a magnitude of ~6. Comet PANSTARRS was visible from both hemispheres in the first weeks of March, and passed closest to Earth on 5 March 2013 at a distance of 1.09 AU. It came to perihelion (closest approach to the Sun) on 10 March 2013. Original estimates predicted that C/2011 L4 would brighten to roughly apparent magnitude 0 (roughly the brightness of Alpha Centauri A or Vega). An estimate in October 2012 predicted that it might brighten to magnitude −4 (roughly equivalent to Venus). In January 2013 there was a noticeable brightening slowdown that suggested that it may only brighten to magnitude +1. During February the brightness curve showed a further slowdown suggesting a perihelion magnitude of around +2.

However, a study using the secular light curve indicates that C/2011 L4 had a "slowdown event" when it was 3.6 AU from the Sun at a magnitude 5.6. The brightness increase rate decreased and the estimated magnitude at perihelion was predicted as +3.5. Comet Halley would be magnitude −1.0 at the same perihelion distance. The same study concluded that C/2011 L4 is very young and belongs to the class of "baby comets" (i.e. those with a photometric age of less than 4 comet years).

When C/2011 L4 reached perihelion in March 2013, the actual peak magnitude turned out to be around +1,

Physical characteristics

Nucleus size

Dust and gas production suggests the comet nucleus is roughly 1 km in diameter, while based on the absolute nuclear magnitude and a geometric albedo of 0.04 the diameter of the nucleus is over 2.4 km. A method based on coma magnitude decay function estimated the effective radius at km.

Rotation period

Light curve measurements taken while the comet was in a brief, lesser active state between July and August 2013 revealed that C/2011 L4 (PanSTARRS) is a fast rotator, spinning on its axis once every five hours.

Orbit

Comet C/2011 L4 (PanSTARRS) likely took millions of years to come from the Oort cloud. After leaving the planetary region of the Solar System, the post-perihelion orbital period (epoch 2050) is estimated to be roughly 107,000 years.

Gallery

File:PanSTARRs And Moon.jpg|Comet PANSTARRS as observed from Southern California, USA, about 3° east of the new crescent Moon File:Comet C2011 L4 (PANSTARRS).png|Photo taken 12 March 2013 in Woodland Hills, Los Angeles, USA. File:Comet C2011L4 PanSTARRS 2013-03-24 in Russia.jpg|Comet C/2011 L4 (PanSTARRS) with a fan-shaped tail 2013-03-24 17:00UT in Special Astrophysical Observatory of the Russian Academy of Science near the village of Nizhny Arkhyz. File:Comet Pan-STARRS.JPG|Photo taken 18 March 2013, at Orbetello, Italy). File:C-2011 Comet PanStarrs taken from the Norman Lockyer Observatory on 26th May 2013 by John Maclean.jpeg|Photo taken by John Maclean at the Norman Lockyer Observatory, Sidmouth, Devon.

References

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| access-date = 12 April 2012 | archive-url = https://web.archive.org/web/20131022151236/http://www.skyandtelescope.com/community/skyblog/observingblog/Comet-PanSTARRS-Still-on-Track-147166535.html | archive-date = 22 October 2013 | url-status = dead

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|access-date = 8 October 2012 |archive-url = https://web.archive.org/web/20130314140227/http://gloria.fzu.cz/en/news/Sledujeme-v%C3%BDvoj-aktivity-komety-Panstarrs |archive-date = 14 March 2013 |url-status = dead

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| access-date = 5 March 2013 | archive-url = https://web.archive.org/web/20130310035648/http://blog.barentsen.be/2013/03/05/map-when-can-you-see-comet-panstarrs/ | archive-date = 10 March 2013 | url-status = dead

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References

1. "MPC Orbit (MPCORB) database - AllComet".
2. Comet Hale–Bopp]] had.[http://www.astrosurf.com/comolli/com39.htm Comet C/2011 L4 (PanSTARRS) with sodium tail - 15 March 2013]