A Tale of Two Comets: MESSENGER Captures Images of Encke and ISON

On November 18, NASA's Mercury-orbiting MESSENGER spacecraft pointed its Mercury Dual Imaging System (MDIS) at 2P/Encke and captured this image of the comet as it sped within 2.3 million miles (3.7 million kilometers) of Mercury's surface. The next day, the probe captured this companion image of C/2012 S1 (ISON), as it cruised by Mercury at a distance of 22.5 million miles (36.2 million kilometers) on its way to its late-November closest approach to the Sun.

MESSENGER's cameras have been acquiring targeted observations of Encke since October 28 and ISON since October 26, although the first faint detections didn't come until early November. During the closest approach of each comet to Mercury, the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) and X-Ray Spectrometer (XRS) instruments also targeted the comets. Observations of ISON conclude on November 26, when the comet passes too close to the Sun, but MESSENGER will continue to monitor Encke with both the imagers and spectrometers through early December.