46P/Wirtanen is a small short-period comet with a current orbital period of 5.4 years. It was one of three comets discovered by astronomer Carl Wirtanen at Lick Observatory in 1948.
On Dec. 16, 2018, 8:06 a.m. EST, less than four days after making its closest approach to the sun, 46P/Wirtanen will pass very close to the Earth — just 7,199,427 miles away. That’s among the 10 closest comet approaches that have occurred since 1950 and the 20th closest approach of a comet dating as far back as the ninth century A.D.
But while that sounds great, 46P likely will not evolve into a spectacular sight.
What we are dealing with is a very small and intrinsically faint comet; ground-based observations combined with images taken with the Hubble Space Telescope in 1996 revealed the nucleus of 46P to have a diameter charitably estimated to be around seven-tenths of a miles.