As the new comet C/2012 S1 (ISON) and the well-known short-period comet 2P/Encke both approach their closest distances to the Sun later this month, they are also passing close to the MESSENGER spacecraft now orbiting the innermost planet Mercury. Just this week, both comets have brightened sufficiently to be captured in images by MESSENGER's wide-angle camera. This figure shows, on the left, images of Encke on three successive days from November 6 to November 8; on the right, images of ISON are shown for three successive days from November 9 to November 11. Both comets appear to brighten each day (top to bottom).
Green circles indicate some of the brighter cataloged background stars in each image; yellow marks bracket the comets. The background stars are fixed in each image from top to bottom, so the motion of the comet relative to the stars is clear in each case. The images have been smoothed slightly to diminish the distracting sharp edges of the pixels.
MESSENGER is viewing these comets from a vantage point that is very different from that of observers on Earth. Comet Encke was approximately 0.5 AU from the Sun and 0.2 AU from MESSENGER when these images were taken; the same distances were approximately 0.75 AU and 0.5 AU, respectively, for ISON. More images will be obtained starting on November 16 when the comets should be both brighter and closer to Mercury.
Dates acquired: 2013 (UT): Nov. 6, 7, 8 (Encke) and Nov. 9, 10, 11 (ISON)
Image Mission Elapsed Time (MET): 26100552, 26190552, 26276500 (Encke), 26330792, 26417208, 26503610 (ISON)
Image ID: 1026100552, 1026190552, 1026276500 (Encke), 1026330792, 1026417208, 1026503610 (ISON)
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: Filter 2 (700 nm)
Resolution: 38 seconds of arc per pixel for Encke, 76 for ISON
Scale: Each tile: 2.85 deg. wide by 0.745 deg. high (Encke), 5.7 deg. wide by 1.49 deg. high (ISON)
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. MESSENGER acquired over 150,000 images and extensive other data sets. MESSENGER is capable of continuing orbital operations until early 2015.
For information regarding the use of images, see the MESSENGER image use policy.