PIA18229: Ice in Egonu and Monk

Ice in Egonu and Monk


Finding evidence for water ice on the planet closest to the Sun was an exciting discovery, but there is still more to learn about Mercury's icy deposits. Regions of permanent shadow seem to be a requirement for water ice to reside on the Solar System's innermost planet, so the large majority of Mercury's water ice deposits are located within impact craters at high latitudes. The two craters shown here, Egonu and Monk, both appear to have areas of permanent shadow and radar-bright deposits (shown in yellow) that are associated with water ice. However these craters are located a fair distance from Mercury's pole, all the way down at 66° latitude! How long can ice stay in these craters? That is just one of the interesting questions about Mercury's water ice deposits still being investigated.

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map covers more than 99% of Mercury's surface with an average resolution of 200 meters/pixel. Images acquired for the surface morphology base map typically are obtained at off-vertical Sun angles (i.e., high incidence angles) and have visible shadows so as to reveal clearly the topographic form of geologic features.

Date acquired: July 20, 2011
Image Mission Elapsed Time (MET): 219648898
Image ID: 528063
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 67.29°
Center Longitude: 63.51° E
Resolution: 133 meters/pixel
Scale: Egonu has a diameter of 25 km (16 miles); Monk has a diameter of 13 km (8 miles)
Incidence Angle: 74.5°
Emission Angle: 0.2°
Phase Angle: 74.5°
Arecibo Radar Image: Shown in yellow, from Harmon et al., Icarus, 211, 37-50 (2011)

Background Info:

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 .

Cataloging Keywords:

Name Value Additional Values
Target Mercury
Target Type Planet
Mission MESSENGER National Astronomy and Ionosphere Center (NAIC)
Instrument Host MESSENGER Arecibo Observatory
Host Type Orbiter Ground-Based Observatory
Instrument Mercury Dual Imaging System (MDIS) Arecibo Radar
Detector Wide Angle Camera (WAC)
Extra Keywords Color, Crater, Impact, Map, Radar, Radio, Shadow, Water
Acquisition Date
Release Date 2014-04-25
Date in Caption 2011-07-20
Image Credit NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Source photojournal.jpl.nasa.gov/catalog/PIA18229
Identifier PIA18229