7P/Pons–Winnecke

Lore & Background

Jean Louis Pons originally discovered the comet on 12 June 1819 from Marseille; it was later rediscovered by Friedrich Winnecke on 9 March 1858 from Bonn. Early calculations for the 1921 apparition suggested a possible collision with Earth in June, but observations on 10 April ruled out an impact. The comet made a very close approach to Earth in June 1927, passing within 0.04 AU (6.0 million km). During its 2021 apparition, eight outbursts were recorded, most of which were ten times greater than observed from other comets like 49P/Arend–Rigaux.

The comet nucleus is estimated to be 5.2 km in diameter. Photometric measurements from the European Southern Observatory revealed brightness variations implying a rotation period roughly between 6.8 and 9.5 hours. Dust production rate was measured at less than 150 kg/s during the 2021 apparition. Gas composition observations at the Calar Alto Observatory determined a typical Jupiter-family composition with some depletion in C3 compounds and a dust-to-mass ratio of 2, suggesting a dust-rich composition.

Reader's Guide

Comet Pons–Winnecke is significant as the progenitor of the June Boötids meteor shower, which is annually seen around June 22 to July 2 with peak activity around June 28. The shower is notably unpredictable, with activity ranging from as low as 2 meteors per hour to outbursts up to 100 meteors per hour. The outward migration of perihelion created impressive meteor showers in 1916, 1921, and 1927, and an outburst in 1998 produced around 200 meteors per hour at its peak. Large meteoroids from this shower have produced occasional fireballs and bolides, two of which reached magnitude -20 and -9 in July 2008 and July 2009 respectively.

The comet's orbit currently has a perihelion of 1.1 AU and an aphelion of 5.6 AU. It passed within 0.04 AU of Earth in June 1927 and 0.1 AU in 1939, but will not come as close in the 21st century. A close approach to Jupiter in July 2037 will drop perihelion to 0.982 AU, and by 2062 perihelion will be further reduced to 0.85 AU. The Jet Propulsion Laboratory proposed a flyby using a flight spare of Mariner 4 in 1969, but the comet's poorly defined ephemeris led to the probe being used for a 1967 Venus flyby as Mariner 5. In 2019, 7P was listed as one of 10 backup targets for the European Space Agency's Comet Interceptor mission, scheduled for launch in 2029, with a possible flyby on 28 September 2033 if selected.

Did You Know?

• During its 2021 apparition, eight outbursts were recorded, most ten times greater than observed from comets like 49P/Arend–Rigaux.
• The June Boötids meteor shower produced an outburst of around 200 meteors per hour in 1998.
• A proposed 1969 flyby using a Mariner 4 spare was canceled due to the comet's poorly defined ephemeris.