[meteorite-list] New MESSENGER Mercury Images

[Ron Baalke]

http://messenger.jhuapl.edu

MESSENGER Mission News
October 1, 2009

NEW MESSENGER MERCURY IMAGES

A Bright Spot in the Latest Imaging

Humans have now had three views of the bright area shown near the top center of this 
image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=336>. 
The first view was as a mere tiny bright spot seen in telescopic images 
of Mercury obtained from Earth by astronomer Ronald Dantowitz. The second view
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=3&gallery_id=2&image_id=236> 
was obtained by the MESSENGER Narrow Angle Camera during the spacecraft's 
second Mercury flyby on October 6, 2008. At that time, the bright feature 
was just on the planet's limb (edge) as seen from MESSENGER. Now MESSENGER 
has provided a new, even better view. The geometry of MESSENGER's third 
Mercury flyby allows us to see the feature and its surroundings in greater 
detail, including the smooth plains in the foreground and the rim of a 
newly discovered impact basin
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=332> 
at lower left. Surprisingly, at the center of the bright halo is an irregular 
depression, which may have formed through volcanic processes. Color images 
from MESSENGER's Wide Angle Camera reveal that the irregular depression 
and bright halo have distinctive color. This area will be of particular 
interest for further observation during MESSENGER's orbital operations 
starting in 2011.

Evening Shadows

These images
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=337> 
were taken on approach to Mercury during the spacecraft's second (left) 
and third (right) flybys. The image from the second flyby was featured 
in an earlier release
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=1&gallery_id=2&image_id=287>. 
The image on the right was taken about 75 minutes before MESSENGER's closest 
approach. The two images cover very nearly the same terrain, but for the 
right image the Sun’s illumination is more nearly grazing (local time 
is almost sunset) and the viewing perspective of the spacecraft is more 
nearly vertical. The large impact crater bisected with a prominent scarp 
or cliff is the same feature in both images. Because of Mercury’s rotation 
between the two encounters, the position of the crater in the right image 
is nearly at the terminator (the division between the dayside and night 
side of the planet), and thus the shadows are longer. The near-grazing 
illumination emphasizes the topography of the crater floor, including 
the relief of the wrinkle ridges on either side of the large scarp. To 
the west of the crater, the shadows and viewing angle show that the terrain 
is far more rugged than it appeared from the second flyby.

Seeing Double?

This image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=338> 
shows a double-ring impact basin, with another large impact crater on 
its south-southwestern side. Smaller, more recent impacts formed comparatively 
fresh craters across the entire surface visible in this image. The floor 
within the inner or peak ring appears to be smoother than the floor between 
the peak ring and the outer rim, possibly the result of lava flows that 
partially flooded the basin some time after impact. Double-ring basins 
are formed when a large meteoroid strikes the surface of a rocky planet.

Crater Ejecta and Chains of Secondary Impacts

This newly observed flat-floored crater
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=339> 
was viewed at an oblique angle as MESSENGER approached Mercury for its 
third flyby, about two hours from closest approach. This crater is younger 
than nearby craters of similar size, indicated by the distinctive halo 
of small secondary craters that radiate outward from the central structure. 
Many of these secondaries are aligned in chain-like formations and some 
show characteristic “herringbone” features pointing back to the crater 
of origin. Crater chains are just one of many ejecta types observed on 
Mercury. Other ejecta features include distinct continuous ejecta
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?image_id=311> 
and crater rays
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?image_id=280>, 
which are composed of both ejecta and secondaries. Another ejecta feature 
of note in this mosaic of two images is a zone of lighter terrain extending 
a bit west of north from the crater itself, possibly providing information 
about the direction of impact. This unnamed crater is partially superposed 
on an older and smaller crater to the south.

Additional information and features from this encounter will be available 
online at http://messenger.jhuapl.edu/mer_flyby3.html. 
Be sure to check back frequently to see the latest released images and 
science results!

________________________________

Highlights from Three Mercury Flybys

Tonight, three MESSENGER team members - Principal Investigator 
Sean Solomon, of the Carnegie Institution of Washington, Project Manager 
Peter Bedini, of APL, and Co-Investigator Louise Prockter, of APL - will 
talk about what we've learned about Mercury from MESSENGER's encounters 
with the planet, and release new pictures from the spacecraft's third 
flyby of Mercury. The event, to be held at the Kossiakoff Center on the 
campus of the Johns Hopkins University Applied Physics Laboratory in Laurel, 
Md., will begin at 5 p.m.
________________________________

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) 
is a NASA-sponsored scientific investigation of the planet Mercury and 
the first space mission designed to orbit the planet closest to the Sun. 
The MESSENGER spacecraft launched on August 3, 2004, and after flybys of 
Earth, Venus, and Mercury will start a yearlong study of its target 
planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution 
of Washington, leads the mission as Principal Investigator. The Johns 
Hopkins University Applied Physics Laboratory built and operates the 
MESSENGER spacecraft and manages this Discovery-class mission for NASA.

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