Secondary Impact Craters on a Lobate Scarp

In and of itself, this image of a portion of a north-south-trending lobate scarp, situated midway between Firdousi crater and Caravaggio basin, is not particularly noteworthy. Look a little closer, however, and this little part of Mercury's surface takes on a strange, pitted appearance. A number of shallow, teardrop-shaped depressions occur throughout the image, aligned from the top-left to the bottom-right. This distinctive surface texture is likely caused by debris thrown out by nearby impacts (there is a crater 11 km, or 7 miles, in diameter to the southeast that might be responsible, for example). If so, then these small depressions are effectively secondary impact craters-but not quite like those we're used to seeing. The difference between these depressions and what we normally think of as secondary craters is likely due to size: as MESSENGER gets closer to the surface of Mercury, we are seeing more and more fascinating features at ever greater resolutions. What else will we see before MESSENGER's adventure ends?

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 200-meter/pixel morphology base map. It is not possible to cover all of Mercury's surface at this high resolution, but typically several areas of high scientific interest are imaged in this mode each week.

Date acquired: July 31, 2014
Image Mission Elapsed Time (MET): 49172453
Image ID: 6788651
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 1.2°
Center Longitude: 77.7° E
Resolution: 23 meters/pixel
Scale: The left-to-right field of view in this image is 21 km (13 miles) across
Incidence Angle: 77.1°
Emission Angle: 1.9°
Phase Angle: 78.9°
Orientation: North is up in this image.

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

Fresh Impact Crater and Rays from Hokusai Crater

At the left edge of this color view is a relatively fresh crater, featured previously in this oblique view. Chains of secondary craters can be seen emanating from the crater, but its bright rays have already nearly faded into the background. Bright, relatively blue rays do cross the scene from northwest to southeast, but these are the famous rays of Hokusai crater, located over 1000 km away.

This image was acquired as a high-resolution targeted color observation. Targeted color observations are images of a small area on Mercury's surface at resolutions higher than the 1-kilometer/pixel 8-color base map. During MESSENGER's one-year primary mission, hundreds of targeted color observations were obtained. During MESSENGER's extended mission, high-resolution targeted color observations are more rare, as the 3-color base map covered Mercury's northern hemisphere with the highest-resolution color images that are possible.

Date acquired: July 05, 2014
Image Mission Elapsed Time (MET): 46889179, 46889199, 46889183
Image ID: 6626955, 6626960, 6626956
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filters: 9, 7, 6 (996, 748, 433 nanometers) in red, green, and blue
Center Latitude: 34.02°
Center Longitude: 39.36° E
Resolution: 223 meters/pixel
Scale: This scene is approximately 260 km (160 miles) across
Incidence Angle: 35.5°
Emission Angle: 45.6°
Phase Angle: 78.2°

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

Secondary Craters in the Northern Plains

This image is one of the highest resolution images taken by the MESSENGER spacecraft to date. It features a field of secondary craters in Mercury's northern smooth plains. Secondary craters are formed by the re-impact of debris strewn from a larger crater. The largest secondary craters in this image are roughly a few hundred meters across. If you look closely, you can see some small craters that are only tens of meters across. All of these craters are simple craters.

This image was acquired as part of the MDIS low-altitude imaging campaign. During MESSENGER's second extended mission, the spacecraft makes a progressively closer approach to Mercury's surface than at any previous point in the mission, enabling the acquisition of high-spatial-resolution data. For spacecraft altitudes below 350 kilometers, NAC images are acquired with pixel scales ranging from 20 meters to as little as 2 meters.

On 25 July 2014, MESSENGER moved closer to Mercury than any spacecraft has before, dropping to an altitude of 100 kilometers (60 miles) above the planet's surface. By 19 August 2014, the minimum altitude will be cut in half, to only 50 kilometers (31 miles)! MESSENGER will execute three more orbit-correction maneuvers in order to delay the end of mission to late March 2015. For more details on this event, read this news story.

Date acquired: June 11, 2014
Image Mission Elapsed Time (MET): 44779109
Image ID: 6477542
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 69.84°
Center Longitude: 48.47° E
Resolution: 2.9 meters/pixel
Scale: This image is about 3 km (1.8 miles) across.
Incidence Angle: 79.4°
Emission Angle: 0.1°
Phase Angle: 79.6°

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

Raditladi Basin Troughs

The troughs of Raditladi are the focus of this high-resolution view inside the peak-ring basin. The troughs, which are largely concentric to the basin, formed through extensional stresses that caused portions of the floor to pull apart. Such extensional features are similar to those observed within Caloris. Some of the small, bright craters that dot Raditladi's floor may be secondaries from Fonteyn crater approximately 900 km away, whose rays appear to cross the basin.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 200-meter/pixel morphology base map. It is not possible to cover all of Mercury's surface at this high resolution, but typically several areas of high scientific interest are imaged in this mode each week.

Date acquired: April 30, 2014
Image Mission Elapsed Time (MET): 41150312
Image ID: 6219297
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 27.79°
Center Longitude: 119.4° E
Resolution: 38 meters/pixel
Scale: This scene is approximately 46 km (29 miles) across
Incidence Angle: 63.9°
Emission Angle: 33.0°
Phase Angle: 97.0°

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

Unnamed Impact Craters

Like Friday's image, today we see Mercury's surface at an image resolution we have rarely come close to before. In this scene, a portion of the rim of an unnamed crater 17 km (11 mi.) in diameter is visible, atop which sits a smaller, later crater (lower center). The prolonged record of impact cratering on Mercury is one of the planet's most visible traits, yet we continue to see the results of that process with ever higher-resolution images. And so, even at resolutions of 9 meters (~30 feet) per pixel, we observe small primary and secondary craters peppering the surface of the innermost planet.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 200-meter/pixel morphology base map. It is not possible to cover all of Mercury's surface at this high resolution, but typically several areas of high scientific interest are imaged in this mode each week.

Date acquired: March 1, 2014
Image Mission Elapsed Time (MET): 35963392
Image ID: 5850686
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 55.89°
Center Longitude: 303.66° E
Resolution: 9 meters/pixel
Scale: The crater in the lower center of the image is approximately 1.8 km (1.1 mi.) across
Incidence Angle: 59.9°
Emission Angle: 27.4°
Phase Angle: 32.5°
North is to the right in this scene.

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

Small Impact Craters

The Sun was barely above the horizon when this image was obtained, and the strong shadows emphasize the ruggedness of the terrain. The surface appears to be almost completely covered by -- or saturated with -- relatively small impact craters (about 2 to 3 km in diameter). Many of these may be secondary craters from a large impact in the vicinity, but it is difficult to tell from which one these small craters originate.

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: January 05, 2012
Image Mission Elapsed Time (MET): 234240885
Image ID: 1226465
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 77.7°
Center Longitude: 214.9° E
Resolution: 137 meters/pixel
Scale: The scene is about 88 km (55 mi.) wide
Incidence Angle: 88.4°
Emission Angle: 39.7°
Phase Angle: 128.1°
North is up in this image.

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

Ghost Crater Near Suisei Planitia

This image features a ghost crater ~55 km (34 mi.) in diameter near its center. The crater was likely flooded by the lava that formed the Suisei Planitia. The crater rim and central peaks can still be seen, despite their burial, and the area was showered by secondary craters from a subsequent impact event.

This image was acquired as part of MDIS's high-incidence-angle base map. The high-incidence-angle base map complements the surface morphology base map of MESSENGER's primary mission that was acquired under generally more moderate incidence angles. High incidence angles, achieved when the Sun is near the horizon, result in long shadows that accentuate the small-scale topography of geologic features. The high-incidence-angle base map was acquired with an average resolution of 200 meters/pixel.

Date acquired: December 09, 2013
Image Mission Elapsed Time (MET): 28935167
Image ID: 5350993
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 63.17°
Center Longitude: 219.7° E
Resolution: 157 meters/pixel
Scale: The ghost crater near the center of the image is approximately 55 km (34 mi.) in diameter.
Incidence Angle: 89.6°
Emission Angle: 52.4°
Phase Angle: 142.0°

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

To Ngoc Van Crater

Crater To Ngoc Van, named for a Vietnamese painter, is seen at the top of this image. The oblique angle provides a great view into the irregularly shaped pit within To Ngoc Van, which is thought to have formed via explosive volcanism and provides evidence for Mercury's geologically active past. Many of the smaller (5-10 km) craters in this scene were produced as secondary impacts from the ejecta of nearby Ahmad Baba crater. North is to the left in this image.

This image was acquired as part of MDIS's high-incidence-angle base map. The high-incidence-angle base map complements the surface morphology base map of MESSENGER's primary mission that was acquired under generally more moderate incidence angles. High incidence angles, achieved when the Sun is near the horizon, result in long shadows that accentuate the small-scale topography of geologic features. The high-incidence-angle base map was acquired with an average resolution of 200 meters/pixel.

Date acquired: November 19, 2013
Image Mission Elapsed Time (MET): 27148228
Image ID: 5223996
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 53.36°
Center Longitude: 239.6° E
Resolution: 154 meters/pixel
Scale: Crater To Ngoc Van is 71 km (44 miles) in diameter
Incidence Angle: 73.7°
Emission Angle: 65.6°
Phase Angle: 30.0°

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

Unnamed Craters

In the center of this image is a high-reflectance area that seems to be confined to a region of lower elevation that is bounded by linear scarp (cliff) segments. Such diffuse bright areas are sometimes related to the deposition of small secondary craters and ray segments by a relatively recent impact crater, but looking at regional images (for example, using QuickMap), there are no rayed craters in the immediate vicinity (though Han Kan might be a candidate). Therefore, a compositional difference may account for the difference in the albedo (brightness) of the material in the low-lying area. Are the scarps tectonic in nature (the result of vertical movement along faults), or were they formed by secondary crater chains? Also of interest in the scene are hollows on the central peak of the crater at the upper left, and the smooth impact melt on the floor of the terrace-walled crater just below center. Scientists will be at work for many years to solve the puzzle of Mercury's complicated geological history!

This image was acquired as part of the NAC ride-along imaging campaign. When data volume is available and MDIS is not acquiring images for its other campaigns, high-resolution NAC images are obtained of the surface. These images are designed not to interfere with other instrument observations but take full advantage of periods during the mission when extra data volume is available.

Date acquired: May 19, 2012
Image Mission Elapsed Time (MET): 245904903
Image ID: 1853014
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -47.3°
Center Longitude: 177.3° E
Resolution: 179 meters/pixel
Scale: The scene is about 184 km (114 mi.) across
Incidence Angle: 47.7°
Emission Angle: 24.2°
Phase Angle: 71.9°

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

Mercurial Limb, One Week Later

What a difference a week makes. Today's featured image was acquired earlier this month, one week after this image (PIA17579), showing how the lighting conditions change in an Earth week (but only about 4% of a Mercury day). Can you spot the crater with the prominent secondary chains? With the Sun now a bit higher above this crater (located about a quarter of the way up from the bottom of the frame), its floor appears smooth, and its crater chains can still be seen to stretch far from its rim.

This image was acquired as part of MDIS's limb imaging campaign. Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb. These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

Date acquired: October 09, 2013
Image Mission Elapsed Time (MET): 23629938
Image ID: 4974132
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: -43.49°
Center Longitude: 150.4° E
Resolution: 1085 meters/pixel
Incidence Angle: 77.7°
Emission Angle: 57.7°
Phase Angle: 132.9°

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

Mercurial Limb

Another day, another beautiful view of Mercury's horizon. In this scene, which was acquired looking from the shadows toward the sunlit side of the planet, a 120-km (75 mile) impact crater stands out near the center. Emanating from this unnamed crater are striking chains of secondary craters, which gouged linear tracks radially away from the crater. While this crater is not especially fresh (its rays have faded into the background), it does appear to have more prominent secondary crater chains than many of its peers.

This image was acquired as part of MDIS's limb imaging campaign. Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb. These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

Date acquired: October 02, 2013
Image Mission Elapsed Time (MET): 23055902
Image ID: 4933174
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: -52.13°
Center Longitude: 167.5° E
Resolution: 667 meters/pixel
Incidence Angle: 82.0°
Emission Angle: 69.4°
Phase Angle: 122.4°

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

Wrinkle Ridge in the Goethe Impact Basin

This view shows the edge of the Goethe Basin. The margins of the basin interior are marked by wrinkle ridges. Part of one such ridge is shown in this image. The scene also includes small secondary crater chains on the smooth plains that fill the basin, and the hummocky terrain outside of the basin.

Date acquired: February 10, 2013
Image Mission Elapsed Time (MET): 2778942, 2778934, 2778938
Image ID: 3491366, 3491364, 3491365
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filters: 9, 7, 6 (996, 748, 433 nanometers) in red, green, and blue
Center Latitude: 82.92°
Center Longitude: 286.5° E
Resolution: 86 meters/pixel
Scale: The small crater in the center of the image is 2.7 km (1.7 miles) in diameter.
Incidence Angle: 88.0°
Emission Angle: 17.5°
Phase Angle: 87.8°

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

Crater Chains Near an Unnamed Impact Crater

This unnamed complex crater in Mercury's northern hemisphere has produced crater chains. These chains form when a crater ejects material that then plummets towards the surface, producing more craters, often in long linear chains. Another set of crater chains can be seen within the large crater in this image, which most likely originated from the crater Hokusai. Since Hokusai's crater chains lie on top of the crater in this image, the crater Hokusai must be younger!

Date acquired: February 01, 2013
Image Mission Elapsed Time (MET): 2001572
Image ID: 3436074
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 54.87°
Center Longitude: 6.15° E
Resolution: 234 meters/pixel
Scale: The large crater is 64 km in diameter (40 miles).
Incidence Angle: 54.9°
Emission Angle: 4.5°
Phase Angle: 50.4°

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

Degraded Impact Crater Rim

The rim of an unnamed peak-ring basin cuts across today's featured image. The basin is relatively degraded, but its rim still stands as a cliff over 1 km (0.6 miles) high. The face of this cliff, where downslope is toward the top of the image, is covered by a chain of secondary craters, whose formation on this steep slope led to somewhat asymmetrical crater shapes. It's hard to say which crater these secondaries originated from - the region is crossed by rays from Bronte, over 1700 km to the west, and Hokusai, over 2000 km to the east.

Date acquired: April 12, 2013
Image Mission Elapsed Time (MET): 8108630
Image ID: 3870271
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 41.15°
Center Longitude: 289.3° E
Resolution: 22 meters/pixel
Scale: This scene is approximately 25 km (16 miles) across
Incidence Angle: 64.0°
Emission Angle: 15.0°
Phase Angle: 79.0°

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

Secondary Craters

This image above shows a common pattern of secondary craters. Secondary craters are formed when blocks of material are thrown out during the formation of an impact crater. The material that impacted the surface to form these secondaries likely originated from the creation of the crater Degas.

Date acquired: November 28, 2012
Image Mission Elapsed Time (MET): 262575756
Image ID: 3038775
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 39.68°
Center Longitude: 231.8° E
Resolution: 24 meters/pixel
Scale: This image is ~27 km ( ~17 mi.) across.
Incidence Angle: 61.4°
Emission Angle: 16.6°
Phase Angle: 78.1°

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

Counting Craters

Counting craters on Mercury is a serious job, as the density of craters on the surface of a planet can be used to indicate its age; the more craters present, the older the surface. Although this technique is commonly used on planetary bodies throughout the Solar System, crater counting on Mercury is particularly challenging. Secondary craters are formed by debris thrown out during an impact, and are often big enough to be confused with primary craters. Their inclusion in crater-counting studies, however, would skew derived age results for a surface, making it appear older than it really is, and so care must be taken when deciding which craters to count, and which to leave out.

Date acquired: November 05, 2012
Image Mission Elapsed Time (MET): 260592647
Image ID: 2897484
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -37.74°
Center Longitude: 194.02° E
Resolution: 117 meters/pixel
Scale: The crater just left of upper center is ~20 km (12 mi.) in diameter
Incidence Angle: 37.9°
Emission Angle: 4.6°
Phase Angle: 38.7°
North is to the right of this image

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

Michelangelo Impact Basin

Here, the peak-ringed Michelangelo basin is seen close to the terminator. Hawthorne crater (outside this image field of view past the upper right corner) may be the source of the secondary crater chains that cross through the basin. North is towards the bottom of this image.

Date acquired: March 26, 2012
Image Mission Elapsed Time (MET): 241236952
Image ID: 1566240
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -44.13°
Center Longitude: 251.5° E
Resolution: 369 meters/pixel
Scale: Michelangelo basin is approximately 230 km (143 mi.) in diameter.
Incidence Angle: 83.6°
Emission Angle: 37.6°
Phase Angle: 67.5°

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

Ellington Basin and Berkel Crater

Ellington basin, named in 2012 for American jazz legend Duke Ellington (1899-1974), is a peak ring basin covered in secondary craters. The prominent crater Berkel lies inside of the basin. Berkel's ejecta and floor exhibit differences in reflectance and color, indicating a heterogeneous local stratigraphy. This image was created by merging a color image with a monochrome image, in order to emphasize both the topography and the color of the area.

Date acquired: August 07, 2012
Image Mission Elapsed Time (MET): 252814064, 252814056, 252814060
Image ID: 2344652, 2344650, 2344651
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filters: 9, 7, 6 (996, 748, 433 nanometers) in red, green, and blue
Center Latitude: -14.85°
Center Longitude: 25.55° E
Resolution: 476 meters/pixel
Scale: Ellington basin is 216 km (134 mi.) in diameter.
Incidence Angle: 19.3°
Emission Angle: 8.7°
Phase Angle: 28.0°

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

Young Impact Crater

This image, taken with the Narrow Angle Camera (NAC), shows an unnamed complex crater in Mercury's southern hemisphere. The sharpness of the terraced walls and central peaks indicate that the crater is relatively young. Also visible is a secondary crater chain that crosses the northern half of the crater floor, most likely created by the ejecta of an impact outside of the field of view.

Date acquired: December 17, 2012
Image Mission Elapsed Time (MET): 264215266
Image ID: 3155492
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -23.01°
Center Longitude: 112.1° E
Resolution: 205 meters/pixel
Scale: This crater is about 75 km (47 mi.) in diameter.
Incidence Angle: 41.0°
Emission Angle: 1.6°
Phase Angle: 39.4°

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

Ray Systems East of Bronte Crater

Today's image shows a complicated area of rays to the east of crater Bronte (named for sisters Charlotte, Emily, and Anne Bronte, and their brother Branwell). The rays trending roughly northeast-southwest originated from Degas, which formed just touching Bronte's rim. The roughly north-south ray (and secondary crater chain) on the right side of the image was probably formed by ejecta that came over the pole from Hokusai.

Date acquired: April 22, 2011
Image Mission Elapsed Time (MET): 211981114
Image ID: 163497
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 38.15°
Center Longitude: 238.4° E
Resolution: 322 meters/pixel
Scale: The edges of the image are about 330 km (205 mi.) long.
Incidence Angle: 62.4°
Emission Angle: 0.2°
Phase Angle: 62.5°

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