Also Known as: Comet 46/Wirtanen
Object Type: Short period comet
Comet Background: A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing.
This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma.
These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma acting upon the nucleus of the comet.
Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles.
The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit.
If sufficiently close and bright, a comet may be seen from Earth without the aid of a telescope and can subtend an arc of up to 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.
Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years.
Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.
Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.
Long-period comets are set in motion towards the Sun by gravitational perturbations from passing stars and the galactic tide.
Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space.
The appearance of a comet is called an apparition.
Discovered by: Comet 46P/Wirtanen was discovered by Carl A. Wirtanen in 1948 at the Lick Observatory, California via photographic plate.
The plate was exposed on 17 January 1948 during a stellar proper motion survey at the observatory.
It took over a year before the object was recognized as a short-period comet due to a lack of observations.
Description: Comet 46P/Wirtanen is a short-period comet with an orbital period of 5.4 years.
The comet is relatively small in size with an estimated diameter of just 1.2 kilometers.
The object was the original target for ESA’s Rosetta spacecraft but the launch window was missed so 67P/Churymov-Gerasimenko was Rosetta’s target in the end.
46P belongs to a small family of comets that boast a higher level of activity than expected for their nucleus size. They emit more water vapor than they should.
This is one of the reasons for added interest in this regular visitor to the proximity of Earth’s orbit.
Wirtanen has a relatively small nucleus, but is part of a small family of hyperactive comets that may contain high amounts of volatile ice.
As it nears our sun, the ice melts and feeds a big, bright coma (the cloudy part, including the tail, of a comet).
Comet 46P-animation
Comet 46/Wirtanan Dec 2018