MESSENGER
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Sander, Munch, and Poe are a trio of impact craters within the Caloris impact basin. Munch and Poe were recently named, while Sander received its name in the first set of feature names after MESSENGER's first Mercury flyby. Munch is named for Edvard Munch (1863-1944), the Norwegian artist and painter of The Scream. The crater Poe takes its name from Edgar Allan Poe, the 19th century American writer and poet. Sander is named for the German photographer August Sander (1876-1964). Sander crater exhibits very bright material within its crater rim, while Munch and Poe each are surrounded by dark material. The presence of both bright and dark materials suggest that there is a diversity of rock types on and below Mercury's surface, with different mineralogical compositions from those of the volcanic plains that comprise the majority of the floor of Caloris basin. The three craters are located in the far northern part of the Caloris basin. The basin rim, indicated by yellow arrows, can be seen in the upper left and extending across the top of this image, and many fractures within Caloris basin are visible in the lower portion of this image. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
A Trio of Craters: Munch, Sander, and Poe
This NAC image displays a number of interesting geologic features characteristic of Mercury's surface. The crater indicated by the yellow arrow has unusual bright material on its floor, likely due to rocks of a different chemical composition. Bright material also has been seen in the craters Sander and Kertesz. The pink arrows point to a pair of larger and older craters that have been flooded with now solidified volcanic lava. In the lower right-hand corner of the image is a large peak-ring basin, about 210 kilometers (130 miles) in diameter, which also appears to have been flooded with lava. There is a small scarp (cliff) within that basin that cuts through a smaller crater at the edge of the basin's inner ring, at the point indicated by the blue arrow. The green arrows on the left side of the image indicate a series of secondary crater chains. Chains of small craters such as these are formed when ejecta are expelled from a primary crater after the initial impact. Unraveling Mercury's geologic history requires investigating the complex and overlapping relationships of volcanic plains, impacts, and scarps seen on the planet's surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Lavas, and Craters, and Scarps! (Oh, My!)
The feature indicated by the white arrow in this NAC image is the newly named crater Enwonwu. It is named in honor of Benedict (Ben) Chukwukadibia Enwonwu, the twentieth century modernist Nigerian sculptor and painter. Enwonwu crater displays a central peak and a set of bright rays emanating from the crater rim. The rays cross the surrounding surface and neighboring craters, indicating that Enwonwu crater was formed comparatively recently in Mercury’s history. The brightness of the rays also suggests relative youth, as over time rays darken and disappear on Mercury's surface. These relationships provide useful indicators for determining the relative ages of features and the sequence of events that have shaped the surface of Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Enwonwu: A Young Crater on Mercury Named for an African Modernist Artist
The crater in the lower right-hand corner of this image has a patch of very dark material located near its center. The region of this image has been seen only with the Sun high overhead in the sky. Such lighting conditions are good for recognizing color differences of rocks but not well suited for ascertaining the topography of surface features from shadows. The shape of the surface in this area is difficult to resolve given the lighting angle, but the dark patch is not in shadow. Dark surfaces have also been seen on other regions of Mercury, including this dark halo imaged during the second Mercury flyby and near such named craters as Nawahi, Atget, and Basho seen during MESSENGER's first Mercury encounter. The example here is particularly striking, however, and from this NAC image the material may appear even darker than in other example areas. The dark color is likely due to rocks that have a different mineralogical composition from that of the surrounding surface. Understanding why these patches of dark rocks are found on Mercury's surface is a question of interest to the MESSENGER Science Team. The right edge of the image here aligns with this previously released NAC image, where other dark surface material, as well as patches of light-colored rocks, can be seen. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
A Patch of Black
The NAC mosaic shown above is being used as the background image for a poster that is advertising this scientific meeting. The mosaic, which shows the western limb of the planet with north to the right, was assembled from individual NAC images acquired as the spacecraft approached the planet during the second Mercury flyby, including three images previously released on October 8, 2008, October 28, 2008, and January 13, 2009. Visible in the mosaic are many lava-flooded craters and large expanses of smooth volcanic plains, which appear similar in texture to volcanically emplaced mare deposits on the Moon. At the microsymposium, scientists will gather to compare and contrast volcanism on the Moon and Mercury, including eruption styles and flux, the timing of volcanism, lava compositions and structures, and linkages between volcanism and the impact history and interior evolution of the two bodies. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Brown University/Carnegie Institution of Washington
 
 
Volcanism on Mercury
This NAC image was taken about 55 minutes before closest approach during the mission's second Mercury flyby. The large crater in the center of the image is near the terminator, the division between the dayside and nightside of the planet. The low angle of the Sun near the terminator causes the long shadows seen here, which reveal that a large scarp or cliff bisects the crater. The crater exhibits a smooth floor broken by slight ridges and seems to have been filled with volcanic lava flows. In the lower left of the crater, the outline of a smaller crater that was filled to its rim by lavas is still visible. The scarp was formed after the large impact crater was filled with the lava flows, for if the scarp had formed first, then the lavas would have flowed over the scarp and buried it. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Shadows Showcase a Steep Scarp
Near the top center of this image is the crater Amaral, recently named for the Brazilian modernist painter Tarsila do Amaral, who lived from 1886 to 1973. Amaral crater, with its smooth floor, surrounding ejecta, and small secondary craters, appears noticeably younger than the heavily cratered surface around it. Along with a smooth crater floor, Amaral also has a central peak. Bright material on this peak is of particular interest to members of the MESSENGER Science Team, as it appears to have an unusual color in images acquired in the 11 color filters of the Wide Angle Camera (WAC). The different color of the central peak likely indicates rocks with different chemical composition from those on the neighboring surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Amaral's Color Palette
This NAC image shows a view of the interior of a newly discovered large impact basin on Mercury, with a diameter of roughly 700 kilometers (430 miles). As seen in this NAC image, the basin floor has a set of radiating fractures that bear a similarity to the extensional troughs of Pantheon Fossae, imaged near the center of Caloris basin during MESSENGER’s first Mercury flyby. The neighboring terrain to the left of this image shows a long scarp within this basin. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
MESSENGER Discovers an Unusual Large Basin on Mercury
In one of the first images transmitted to Earth following MESSENGER's second Mercury flyby, a full-planet departure view showed a crater in the northern region near the planet's limb with an impressively large system of rays. The WAC image shown here is part of a 3x3 mosaic and provides a closer look at that extensive ray system. Astronomers who collected ground-based radar images from the Arecibo Observatory had identified this rayed crater prior to MESSENGER's flyby and referred to it as feature
 
 
A Big and Brilliant Ray System
Acquired as the MESSENGER spacecraft approached the planet during the mission's second Mercury flyby, this NAC image captures a scene of nightfall on Mercury. The surface features on the right side of the image are illuminated by the last rays of sunlight and will soon be in the darkness of a Mercury night. Some high-standing rugged crater rims poke up into the light, while the lower-elevation crater interiors are already in darkness. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Night Falls on Mercury
The crater surrounded by dark material located just below and to the left of the center of this NAC image is the newly named crater Nawahi. The crater is named in honor of Joseph Kaho'oluhi Nawahiokalaniopuu, the 19th century native Hawaiian painter. Nawahi crater is located within the large Caloris impact basin, and the hills and rugged terrain to the left of Nawahi in this image are part of the basin rim. The unusual dark material creating a halo around Nawahi makes this crater of special interest, as the dark material likely represents rocks with a different chemical and mineralogical composition than those of the neighboring surface. A portion of the newly named crater Munch is also visible on the upper right edge of this image. Munch is also rimmed by dark material. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Say Aloha to Nawahi!
Visible near the top of this NAC image are two distinctive craters, imaged for the first time during MESSENGER’s second Mercury flyby. The crater at upper left has light-colored material around its rim and on its floor. In contrast, the larger crater to the right is surrounded by a halo of dark material. The dark and light materials likely represent rocks with different chemical and mineralogical compositions and as such offer an opportunity to learn about variations in the components that make up Mercury’s surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
A Study in Dark and Light
In the lower center of this NAC image, a scarp cuts through two craters (blue arrows). The fact that the scarp transects the craters indicates that it formed after the two crater-forming impact events. Many similar scarps, referred to as rupes, have been identified on Mercury, and rupes are believed to have formed when the interior of Mercury cooled and the planet shrank slightly. The white stripe that cuts diagonally across this NAC image (red arrows) is part of a system of rays emanating from a bright, relatively young crater to the north. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
A Rupes and a Ray
Taken about 28 minutes following MESSENGER's closest approach during the mission's second Mercury flyby, this NAC image, just one of a large mosaic set, focuses in on an impact basin with a nicely developed peak-ring structure. Subsequent impact events have resulted in smaller craters superimposed on top of the larger peak-ring basin. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
 
 
Peak-Ring Basin Close-Up from the Second Mercury Flyby
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
At the Edge of a World
This WAC image shows a close-up view of the crater Rudaki, named for the Persian poet of the late 800s and early 900s. On the floor of Rudaki and also in a broad region surrounding Rudaki to the west are smooth plains, which are far less cratered than the neighboring terrain (except for the small secondary craters from the large, fresh crater to the west of Rudaki). Detailed studies of Mariner 10 images led to the conclusion that these plains near Rudaki were formed by volcanic flows on the surface of Mercury. This image from MESSENGER's second flyby of Mercury shows some nice examples of craters in the plains that appear to have been significantly flooded with lava, leaving only their circular rims preserved. This WAC image is one of five scenes in a high-resolution color mosaic obtained just after MESSENGER's closest approach to Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
Volcanic Plains on Mercury
A dominant feature in this NAC image is the large expanse of smooth plains in the upper left of the view. It may be related to extensive plains in Mercury's high northern latitudes that were identified in Mariner 10 images. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
Looking Toward Mercury's North Pole
MESSENGER's second Mercury flyby passed over the opposite side of the planet from that seen during the mission's first Mercury encounter. Visible in the recently obtained image shown here are many features also seen by Mariner 10: Shevchenko crater named for the 19th century Ukrainian poet, Khansa for the Arabic poet of the 7th century, Rabelais for the Renaissance French writer, Holberg for the Norwegian-Danish writer of the 18th century, Spitteler for the Swiss epic poet who won the Nobel Prize for Literature in 1919, Rameau for the Baroque-era French composer, Puccini for the Italian composer of the late 1800s and early 1900s, and Horace for the ancient Roman poet. Discovery Rupes cuts through Rameau and is named for the ship of English explorer Captain James Cook. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
A View to the South... from the Other Side of Mercury
The first image taken following MESSENGER's closest distance to Mercury during the mission's recent flyby was a Wide Angle Camera (WAC) image. The image shown here is the first NAC image acquired after closest approach, and since the resolution of the NAC is a factor of seven higher than that of the WAC, this image is the highest-resolution image obtained during MESSENGER's second Mercury flyby. The image was taken near local dawn, so the shadows are long and many features are shrouded in darkness. This portion of Mercury's surface is heavily cratered, with small craters visible down to the limits of even this highest-resolution image. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
The Highest-resolution Image from MESSENGER's Second Mercury Flyby
This NAC image shows a bright crater with an extensive system of impact ejecta rays. The impact crater and its associated system of rays were originally detected in 1969 as a
 
 
'A' Spectacular Rayed Crater
This dramatic NAC image was acquired about 56 minutes prior to MESSENGER’s closest approach during the mission’s recent Mercury flyby, as the spacecraft approached the planet's illuminated crescent. Prominent toward the horizon in this view of newly imaged terrain is a long cliff face. A small impact crater (about 30 kilometers, or 19 miles, in diameter) overlies this lengthy scarp. The scarp extends for over 400 kilometers (250 miles) and likely represents a sign of aging unique to Mercury among the planets in the Solar System. As time passes, the interior of a planet cools. However, the relative size of Mercury's central metallic core is larger than that of the other planets and hence has significantly affected the planet’s geologic evolution. The numerous long scarps on Mercury are believed to be the surface expression of faults formed in the rocks of Mercury's crust as the interior of the planet cooled and contracted. This contraction compressed the surface and thrust some sections of crust over others, creating long curving cliffs like the one shown here. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
Mercury Shows Signs of Aging
The gallery of images acquired by the MESSENGER mission is filled with both Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) images. The two MDIS cameras, though they cannot operate simultaneously, are used together in a complementary fashion. The NAC acquires images at a factor of seven higher spatial resolution than the WAC, while the WAC is equipped with 11 narrow-band color filters; thus, the NAC can see features in much more detail, but the WAC can see them in color. This NAC image was taken just 22 seconds prior to the beginning of a set of WAC images used to create full-planet color images of Mercury. The higher resolution of the NAC is evident by comparing these narrow and wide views of the same scene, taken back-to-back. In this NAC image, bright rays from nearby Kuiper crater enter the frame from the bottom of the image. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
Mercury as Seen in Both Narrow and Wide Views
This NAC image, taken about 85 minutes after MESSENGER's closest approach during the mission's second Mercury flyby, shows a view of Astrolabe Rupes, named for the ship of the French explorer Jules Dumont d'Urville. Rupes is the Latin word for cliff. Mercury's day/night transition (the terminator) is located on the left side of the image, and the Sun is striking the cliff face of Astrolabe Rupes in the upper right of the image. Also visible in the image are additional unnamed rupes, whose cliff faces are casting dark shadows. One of these rupes intersects the crater Ghiberti, named for the Italian Renaissance sculptor. Rupes on Mercury are thought to have formed as the interior of Mercury cooled and the planet consequently contracted slightly. Determining the number and extent of rupes on Mercury can thus be used to understand the thermal history of the planet. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington.
 
 
Astrolabe Rupes and More
In both the optical navigation images and the full-planet Wide Angle Camera (WAC) approach frame, a bright feature is clearly visible in the northern portion of the crescent-shaped Mercury. This NAC image resolves details of this bright feature, showing that it surrounds a small crater about 30 kilometers (19 miles) in diameter, seen nearly edge-on. Presumably, the bright material was ejected from this small crater, which apparently formed relatively recently in Mercury's past, because Mercury's surface materials tend to darken with time. The brilliant ejecta are so bright compared with the neighboring surface that Earth-based telescopic observations also detected this feature, despite its being associated with such a small crater. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington.
 
 
A Small Crater Makes a Bright Impact
To the human eye, Mercury shows little color variation, especially in comparison to a colorful planet like Earth. But when images taken through many color filters are used in combination, differences in the properties of Mercury's surface can create a strikingly colorful view of the innermost planet. Shown here are two color images of Thakur, named for the Bengali poet, novelist, and Nobel laureate influential in the late 19th and early 20th centuries. The image on the left was produced by combining images from three WAC filters into red, green, and blue channels, as a general representation of the color seen by the human eye. The right image was created by statistically comparing and contrasting images taken through all 11 of the WAC's narrow-band color filters, which are sensitive to light not only in the visible portion of the spectrum but also to light that the human eye cannot see. This method greatly enhances subtle color differences in the rocks of Mercury's surface, providing insight into the compositional variations present on Mercury and the geologic processes that created those color differences. Visible on the floor of Thakur crater is the intersection of two ridges, seen here in unprecedented detail for the first time with MESSENGER's newly obtained images. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington.
 
 
Exposing Mercury's Colors
When a meteoroid strikes the surface of a planet, material from the surface is ejected outward at high velocity, often creating rays that extend over distances far greater than the size of the crater formed by the impact. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
Dark Rays on Mercury
Believe it or not, these two images show the same terrain on Mercury as imaged by Mariner 10 in the 1970s and by the MESSENGER spacecraft on October 6, 2008. The reason it looks so different is that the angle that the Sun illuminates the surface is dramatically different between the two observations. When Mariner 10 acquired the image on the left, the Sun was high in the sky, which highlights the relative differences in brightness between geologic units on the surface. When the Sun is lower in the sky, as was the case during the second MESSENGER Mercury flyby (right image), shadows become more prominent and it is easier to see the rugged topography of the surface. Most noticeably, a peak-ring impact crater with a diameter of about 150 kilometers (93 miles) is clearly seen in new MESSENGER data, whereas it was nearly invisible in Mariner 10 data. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
A New Look at Old Terrain
Extending from the left edge of this image downward toward the lower right corner is a long cliff face. This cliff runs through a large ancient crater in the center of the frame. Cliffs such as this one, referred to as rupes on Mercury, have been identified on other areas of the planet, such as Beagle Rupes imaged during MESSENGER's first flyby. This rupes is being seen for the first time, as this portion of Mercury's surface is located within the
 
 
A Cliff Runs Through It
About 69 minutes after MESSENGER's closest approach to Mercury during the mission's second flyby, the NAC acquired this image of a portion of Mercury's surface also seen during the Mariner 10 mission. Toward the lower portion of the image, Arecibo Vallis is visible. Vallis is the Latin word for valley, and valles (the plural of vallis) on Mercury are named for radio telescope observatories. Arecibo Observatory is located in Puerto Rico and has been used to conduct Earth-based studies of Mercury with important results, including the detection of radar-bright materials at Mercury's poles that may be water ice trapped in permanently shadowed craters. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
MESSENGER Observes Arecibo
By examining the characteristics of craters and their relationships to each other, geologists are able to unravel the history of Mercury. This image shows a northern portion of Mercury's surface, looking at the terminator (the transition from the sunlit dayside to the dark night side of the planet). The crater in the lower left, Vyasa, has a rough floor, with other craters superimposed onto it, indicating that this crater is relatively old. In contrast, the neighboring crater, Stravinsky, has a much smoother floor and appears to overlap the rim of Vyasa, suggesting that this crater is relatively younger. These craters appear to be aptly named to support this relative age relationship; Vyasa is named for the ancient Indian poet from about 1500 BC, while Igor Stravinsky was a 20th century Russian-born composer. The nearby crater Rubens, named for the 17th century Flemish painter, may indeed represent an event intermediate in time between Vyasa and Stravinsky. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
 
 
Mercury Through Time
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