NASA’s Hubble Space Telescope photographed comet 46P/Wirtanen on December 13, when the comet was 7.4 million miles (12 million kilometers) from Earth. In the image, the comet’s nucleus is hidden in the center of a fuzzy glow from the comet’s coma. The coma is a cloud of gas and dust that the comet has ejected during its pass through the inner solar system due to heating from the Sun.
To make this composite image, the color blue was applied to high-resolution grayscale exposures acquired from the spacecraft's WFC3 instrument.
The inner part of a comet’s coma is normally not accessible from Earth. The close fly-by of comet 46P/Wirtanen allowed astronomers to study it in detail. They combined the unique capabilities of Hubble, NASA’s Chandra X-ray Observatory, and the Neil Gehrels-Swift observatory to study how gases are released from the nucleus, what the comet’s ices are composed of, and how gas in the coma is chemically altered by sunlight and solar radiation.
Comet 46P/Wirtanen made its closest approach to Earth on December 16, when it passed just over 7 million miles (11 million kilometers) from our planet, about 30 times farther away than the Moon. Although it is the brightest comet of 2018, 46P/Wirtanen is only barely visible to the unaided eye. It is best viewed through binoculars or a telescope. Backyard observers can currently find the comet within the constellation Taurus, between the Pleiades and Hyades star clusters.
Comet 46P/Wirtanen orbits the Sun once every 5.4 years, much quicker than the 75-year orbit of the more famous Comet Halley. Most of its passes through the inner solar system are much farther from Earth, making this year’s display particularly notable.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.