NASA MESSENGER Image: Comet C/2012 S1 aka ISON

NASA's MESSENGER spacecraft took this image of comet C/2012 S1 (ISON) during its closest approach of Mercury at 01:54:30 UTC on November 20. 

ISON was approximately 22.5 million miles (36.2 million kilometers) from MESSENGER and 42.1 million miles (67.8 million kilometers) from the sun. 

The image is 7° by 4.7° in size and has been slightly magnified and smoothed to enhance the faint tail of the comet. 

The tail was oriented at an angle to MESSENGER at the time and is foreshortened in this image; however, some faint structure can still be seen.

This image was acquired by the Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) aboard NASA's MESSENGER spacecraft. 

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Southwest Research Institute

NASA ESA Hubble Captures distant image of Comet ISON

Comet ISON may appear brighter than the full Moon around the time it approaches the Sun Nov. 28, but it is not yet visible to the naked eye. 

The Hubble Space Telescope snapped this image as ISON hurtles toward the sun at about 47,000 miles.

The NASA Hubble Space Telescope has given astronomers their clearest view yet of Comet ISON, a newly-discovered sun grazer comet that may light up the sky later this year, or come so close to the Sun that it disintegrates.

A University of Maryland-led research team is closely following ISON, which offers a rare opportunity to witness a comet's evolution as it makes its first-ever journey through the inner solar system.

Like all comets, ISON is a "dirty snowball" – a clump of frozen gases mixed with dust, formed in a distant reach of the solar system, traveling on an orbit influenced by the gravitational pull of the Sun and its planets.

ISON's orbit will bring it to a perihelion, or maximum approach to the Sun, of 700,000 miles on November 28, said Maryland assistant research scientist Michael S. Kelley.

Read Kelley's comprehensive blog on Comet ISON here

This image was made on April 10, when ISON was some 386 million miles from the Sun – slightly closer to the Sun than the planet Jupiter.

Comets become more active as they near the inner solar system, where the Sun's heat evaporates their ices into jets of gases and dust but even at this great distance ISON is already active, with a strong jet blasting dust particles off its nucleus.

As these dust particles shimmer in reflected sunlight, a portion of the comet's tail becomes visible in the Hubble image.