Comet Encke

MESSENGER image of comet 2P/Encke during its closest approach to Mercury. At that time, Encke was approximately 2.3 million miles (3.7 million kilometers) from MESSENGER and 32.7 million miles (52.6 million kilometers) from the Sun. The image is 7° by 4.7° in size and has been slightly smoothed to enhance the faint tail of the comet. The tail was oriented nearly side on to MESSENGER in this image and is seen to stretch several degrees from the comet's bright coma in the direction away from the Sun.

MESSENGER's cameras have been acquiring targeted observations (watch an animation here) 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. Read this mission news story for more details.

Date acquired: 22:56 UTC on November 17, 2013
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)

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

Note: For more information, see PIA17693: MESSENGER's First Images of Comets Encke and ISON and Two Comets to Fly By Mercury.

Mapping Beethoven

At top, the white line highlights the region of Mercury's surface visible to the XRS during a solar flare on 16 June 2011. Near the center is the ~650-km-diameter Beethoven impact basin at 21° S, 236° E. This region has a higher Mg/Si ratio than the northern plains and is closer in composition to terrestrial komatiites, low-silica, high-temperature volcanic rocks that formed only very early in Earth's history.

Below, smooth plains within the same area have been mapped. In green are plains of volcanic origin. These plains display flooding and embayment relationships and color contrasts typical of volcanic plains on Mercury. Yellow denotes plains of uncertain origin. Though they may also be volcanic, they lack definitive evidence for a volcanic origin and may have formed as fluidized impact ejecta, possibly from the Beethoven impact basin, or as impact melt. In blue are plains that formed when rock was melted by impacts. Even geologically complex regions, such as the area seen here, are often dominated by volcanic deposits, and their compositions are consistent with a volcanic origin.

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

A Northern Footprint

The X-Ray Spectrometer (XRS) on MESSENGER collects compositional information for relatively large regions on Mercury's surface, and strong signals are only received during times of high solar activity. The blue region outlined in this wide-angle camera image mosaic shows the region visible to the XRS during a solar flare on 16 April 2011. The XRS data indicates that the area is basaltic in composition, the same type of volcanic rock that comprises the lunar maria. This region is part of the vast, high-reflectance northern plains that cover approximately 6% of Mercury's surface. The 1000, 750, and 430 nm bands of the Wide Angle Camera are displayed in red, green, and blue, respectively.

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington