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DAWN - Bild des Tages - Dezember 2011

	12.12.2011 - Happy holidays Image of the Day is taking a break for the holidays and will be back on Monday January 9th. Happy holidays!
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13.12.2011 - Topography and albedo image of Oppia crater

These Dawn FC (framing camera) images show Oppia crater, after which Oppia quadrangle is named. Oppia crater is a distinctive crater because it has an unusually shaped rim, which is almost rectangular in form. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas at the bottom of the image are the highest areas and the blue area in the center of Oppia crater and at the top of the image are the lowest areas. The landslide/ slump features running into the center of Oppia crater are distinctive in both the albedo and topography images. There is an area above Oppia crater, which contains 2 small impact craters, that looks like a depression in the albedo image. But in the topography image it is clear that there is not much of a height difference between this area and the surrounding terrain.

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12.12.2011 - Topography and albedo image of Numisia crater

These Dawn FC (framing camera) images show the ~20km diameter Numisia crater, after which Numisia quadrangle is named. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white area at the top of the image is the highest area and the blue area in the center of Numisia crater is the lowest area. The color-coded height image shows that Numisia crater impacted a relatively high (colored red) area and that Numisia crater is reasonably deep with steep sides. A smaller, more degraded impact crater, underneath Numisia crater to the right, is more clearly visible in the color-coded height image than in the albedo image. In the albedo image both dark and bright material is seen cropping out of and slumping down into Numisia crater.

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11.12.2011 - Topography and albedo image of Marcia crater

These Dawn FC (framing camera) images show Marcia crater, after which Marcia quadrangle is named. Marcia crater is the largest and southernmost of the three Vestan craters nicknamed the ‘Snowman’. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas on the right of the image are the highest areas and the blue area in the center of Marcia crater is the lowest area. Marcia crater is a fresh crater with an irregularly shaped rim, which is clear in both the albedo and color-coded height images. Dark material cropping out of the rim and slumping into the center of Marcia crater is visible in the albedo image. The right side of Marcia crater has a reasonably steep slope, which is clear in the color-coded height image as the relatively rapid change in colors towards Marcia’s center.

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10.12.2011 - Topography and albedo image of Lucaria Tholus

These Dawn FC (framing camera) images show Lucaria Tholus, after which Lucaria quadrangle is named. Lucaria Tholus is the large, roughly elliptically shaped hill in the center of the image. ‘Tholus’ is a geological word used to describe a hill or mountain. Lucaria is the only quadrangle not named after a crater or basin. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas on Lucaria Tholus are the highest areas and the blue area at the bottom of the image is the lowest area. Lucaria Tholus has prominent topography (seen in the right image) and has dark material covering some of it (seen in the left image).

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09.12.2011 - Topography and albedo image of Gegania crater

These Dawn FC (framing camera) images show Gegania crater, after which Gegania quadrangle is named. Gegania crater is the large, ~15km diameter crater, at the bottom of the image. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas in the bottom half of the image are the highest areas and the blue area at the top of the image is the lowest area. Gegania crater is distinctive because it has an irregularly shaped rim that makes it almost a square shape instead of a circle. Also, it is the eastern half of a double impact crater. A part of the western part of the double impact crater can be seen more clearly in the color-coded height image as a roughly circular depression.

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08.12.2011 - Topography and albedo image of Floronia crater

These Dawn FC (framing camera) images show the 12km diameter Floronia crater, after which Floronia quadrangle is named. Floronia crater is the middle crater in the vertical column of 3 craters, which are slightly offset from the center of the image. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas at the bottom of the image are the highest areas and the blue area at the top of the image is the lowest area. The color-coded height image shows Floronia crater to be reasonably deep as it grades from a green color at the rim to a blue color further into its interior.

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07.12.2011 - Topography and albedo image of Domitia crater

These Dawn FC (framing camera) images are dominated by the 45km diameter Domitia crater, after which Domitia quadrangle is named. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas at the bottom of the image are the highest areas and the blue area at the top of the image is the lowest area. Domitia crater is seen to be a deep crater in the color-coded height image and the many smaller impact craters along its rim are clear in the albedo image.

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06.12.2011 - Topography and albedo image of Claudia crater

These Dawn FC (framing camera) images show Claudia crater (marked by an arrow) and its surroundings. Claudia crater is the crater which is used to define 0° longitude on Vesta. Claudia crater was chosen for this for many reasons. Firstly, it is in a longitude region of Vesta that does not have many prominent/ significant features. The region in which 0° longitude is defined will be split in two and it is important not to split prominent/ significant features. Secondly, it is located near Vesta’s equator and is a small crater (~700m across) so this increases the accuracy of the location of 0° longitude. Thirdly, it is reasonably easy to locate. In order to find it first find the large, ~15km diameter, crater with the ~5km diameter impact crater on its rim. Then find the double degraded craters, which are each ~5km in diameter, and are ~10km east of the ~15km diameter crater. These double craters have a small, <1km diameter, crater on their rim. Claudia is ~3km to the west of this crater. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas across the center of the image are the highest areas and the blue and green areas in the top and bottom of the image are the lowest areas.

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05.12.2011 - Topography and albedo image of Bellicia crater

These Dawn FC (framing camera) images are dominated by the 35km diameter Bellicia crater, after which Bellicia quadrangle is named. The left image is an albedo image, which is taken directly through the clear filter of the FC. Such an image shows the albedo (eg. brightness/ darkness) of the surface. The right image uses the same albedo image as its base but then a color-coded height representation of the topography is overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, allowing stereo reconstruction. The various colors correspond to the height of the area. The white and red areas in the bottom half of the image are the highest areas and the blue areas in the top half of the image are the lowest areas. The fresh, sharp rim of Bellicia crater can be seen in both images and it also has two smaller impact craters on its rim. The crater on the bottom part of the rim is reasonably deep and mostly in shadow. But the crater on the top part of the rim is mostly eroded and can only be seen as a perturbation in the rim of Bellicia crater. This rim crater does not show a clear topography difference to Bellicia crater in the color-coded topography image. It is possible that most of this crater slumped into Bellicia crater.

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04.12.2011 - Rocks from Vesta – Part 3: Diogenites

The HED (howardite, eucrite and diogenite) meteorites are a large group of meteorites believed to originate from Vesta, a hypothesis that is consistent with current Dawn observations. The diogenites originated deep within the crust of Vesta and resemble rocks, both in texture and composition, which we find in the lower crust of the Earth. The QUE 99050 (left) and GRA 98108 (right) diogenites, pictured here, were recovered in Antarctica. These images are of thin slices of the meteorites as viewed through a polarizing microscope. The white bars in the images, each 2 millimeters long, indicate the scale. When polarized light passes through thin slices of rock, different minerals have different colors. QUE 99050 (left) consists of large gray and yellow crystals of pyroxene (magnesium-iron silicate) and is a subgroup of diogenite called “orthopyroxenitic diogenite” (orthopyroxenite is the name of a rock composed primarily of the mineral orthopyroxene). GRA 98108 (right) has a more mafic (i.e. magnesium and iron rich) mineralogy, consisting of roughly equal portions of pyroxene and the much brighter colored olivine, a silica-poor iron magnesium-iron silicate. This olivine-rich “harzburgitic diogenite” (harzburgite is the name given to a rock composed of a mixture of the minerals orthopyroxene and olivine) is thought to represent the most deep-seated rocks from Vesta that we have in the meteorite collection. Diogenites like these comprise some fraction of Vesta’s lower crust, and their compositions can be compared with observations from various instruments aboard Dawn. They can be compared with the VIR (Visible and Infrared Imaging Spectrometer) spectra to determine mineralogy and with the GRaND (Gamma Ray and Neutron Detector) observations to calibrate and interpret the GRaND instrument’s responses. Similar rocks have likely been excavated by large impacts, such as the one that formed the Rheasilvia basin at the south pole of Vesta.

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03.12.2011 - Rocks from Vesta – Part 2: Howardites

The HED (howardite, eucrite and diogenite) meteorites are a large group of meteorites believed to originate from Vesta, a hypothesis that is consistent with current Dawn observations. Howardites are regolith breccia rocks, meaning that they formed through the grinding and fusion of rock and dust that occurs during meteor impacts on the surface of Vesta. Howardites are comprised of fragments of eucrite and diogenite of varying grain sizes, which can be seen in this picture of the Bununu howardite. This sample weighs 217 grams and was recovered in 1942 in Africa. Along with fragments of eucrite and diogenite, some howardites also contain solar wind implanted noble gasses, which confirms that they once resided on the surface of their parent body. This makes howardites a good laboratory analog for spectral and chemical measurements that will be made of the Vestan surface by Dawn.

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02.12.2011 - Rocks from Vesta – Part 1: Eucrites

The HED (howardite, eucrite and diogenite) meteorites are a large group of meteorites believed to originate from Vesta, a hypothesis that is consistent with current Dawn observations. The eucrites are crystallized lavas that have the composition of basalt, the most common lava type on the Earth. The QUE 97053 (left) and EET 90020 (right) eucrites, pictured here, were recovered in Antarctica. These images are of thin slices of the meteorites as viewed through a polarizing microscope. The white bars in the images, each 2.5 millimeters long, indicate the scale. When polarized light passes through thin slices of rock, different minerals have different colors. QUE97053 (left) consists mostly of elongated gray crystals of feldspar (calcium aluminum silicate) and brightly colored grains of pyroxene (magnesium iron silicate). The texture of this rock is what would be expected from crystallization of a molten magma. EET90020 (right) has similar mineralogy but a recrystallized texture of equant grains formed by later heating. Equant grains have the same or roughly the same dimensions in all directions. Eucrites like these comprise some fraction of Vesta’s surface. Their compositions can be compared with observations from various instruments aboard Dawn. They can be compared with the VIR (Visible and Infrared Imaging Spectrometer) spectra to determine mineralogy and with the GRaND (Gamma Ray and Neutron Detector) observations to calibrate and interpret the GRaND instrument’s responses.

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01.12.2011 - Caparronia crater covered with ejecta and small, secondary craters

This Dawn FC (framing camera) image is dominated by Caparronia impact crater. Caparronia crater is approximately 55 km in diameter and has a mostly fresh, irregularly shaped rim. It also has a curved, linear mound running across most of its base. For all of these reasons Caparronia is a distinctive crater and this is why it was chosen to name the quadrangle in which it is situated. The smooth region around Caparronia crater is most likely fine impact ejecta, which were thrown out from the crater at the time of its formation. Other impact related features are the linear chains of small, less than 1km, secondary craters that occur throughout the image. Some particularly distinctive crater chains are in the bottom part of the image. Secondary crater chains are formed when relatively large debris are ejected from an impact and skip along the surface, much like a stone skipping across a lake. There are also some linear scars running diagonally across the image, which are due to debris scouring across the surface.

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