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DAWN - Bild des Tages - Februar 2012

29.02.2012 - Dust-covered surface with fresh small craters

This Dawn FC (framing camera) image shows a relatively smooth part of Vesta’s surface. This smooth texture is probably due to the surface being covered in a layer of tiny dust particles. Generally, smaller particles look smoother than larger particles in images such as those taken by Dawn of Vesta. The outlines of some old, degraded craters can be seen below this later of dust. On top of this dust layer are young, small, fresh craters, which must have been formed by objects hitting the surface since the dust layer was laid down. There are also a number of grooves, running diagonally across the image, on top of the dust layer.

28.02.2012 - Light and shadow

This Dawn FC (framing camera) image shows an area in Vesta’s northern hemisphere that has been illuminated more by the sun than yesterday’s image of the day. More of the landscape in this image has been illuminated because this area is located at a slightly lower latitude than yesterday’s image of the day. As Vesta progresses from its winter to its spring the sunlight is creeping further and further northwards. There are many craters visible in this image, which is consistent with this area being located in Vesta’s heavily cratered northern hemisphere. There is also a distinctive groove, which is roughly 10 kilometers (6 miles) long, in the left center of the image that is highlighted by the sunlight.

27.02.2012 - Islands in the darkness

This Dawn FC (framing camera) image shows a part of Vesta’s northern hemisphere, which is mostly in darkness. Since Dawn’s arrival at Vesta the sun has not illuminated Vesta’s most northerly latitudes. This is because the tilt of Vesta with respect to the sun has not been suitable for illuminating these parts of the asteroid. But, as Vesta progresses from its winter to its spring more of these northerly latitudes are being illuminated. As seen in this image the illumination begins by the low-angled sun revealing a few higher elevation parts of the surface, while the rest of the lower-lying surface is still covered in darkness. More of this area will need to be illuminated for any meaningful interpretations of it to take place.

24.02.2012 - Cornelia crater

This Dawn FC (framing camera) image shows Cornelia crater, a roughly 15-kilometer-diameter (9-mile-diameter) crater with a sharp, fresh rim. Cornelia crater has a spectacular internal structure, which consists of bright and dark material. This bright and dark material slumps from the rim and the sides of the crater towards the center of the crater. The top rim of Cornelia crater has partly collapsed and is also slumping towards the center of the crater. This crater has some dark rays, emanating from its rim, which extend for up to 10 kilometers (6 miles). The area immediately surrounding Cornelia crater is relatively smoother than the adjacent terrain. This indicates that there is a layer of fine-grained ejecta, which was ejected from the crater during its formation, surrounding it.

23.02.2012 - Apparent brightness and topography images of Cornelia crater

The left-hand image is a Dawn FC (framing camera) image, which shows the apparent brightness of Vesta’s surface. The right-hand image is based on this apparent brightness image, which has had a color-coded height representation of the topography overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, which allows stereo reconstruction. The various colors correspond to the height of the area. The white and red areas in the topography image are the highest areas and the blue areas are the lowest areas. It is clear from both of the images that the two craters are depressions, which have lower elevations than the surrounding areas. But, the topography image shows that the left side of the image has a higher elevation than the right side, something that is not clear in the apparent brightness image.

22.02.2012 - Aricia Tholus

This Dawn FC (framing camera) image shows Aricia Tholus, the dark hill that was presented in the previous Image of the Day. Tholus is a word used to describe a small dome-like mountain or hill. Aricia was the name of a city in ancient Italy. Aricia Tholus has a roughly 2 kilometer (1 mile) diameter crater near its summit, which is surrounded by a dark area. Dark rays extend from the summit for more than 10 kilometers (6 miles). The origin and formation mechanism of Aricia Tholus is currently under discussion. Also visible in this image are narrow, linear depressions (top left corner) and many degraded craters of various sizes.

21.02.2012 - Brightness and topography images of a dark hill

The left-hand image is a Dawn FC (framing camera) brightness image, which shows the brightness/ darkness of Vesta’s surface. The right-hand image is based on this brightness image, which has had a color-coded height representation of topography overlain onto it. The topography is calculated from a set of images that were observed from different viewing directions, which allows stereo reconstruction. The various colors correspond to the height of the area. The white and red areas in the center and bottom of the topography image are the highest areas and the blue area in the top of the image is the lowest area. The dark hill shows up clearly as a red, high topography feature in the topography image.

20.02.2012 - Dawn on Vesta

This Dawn FC (framing camera) image shows the sun illuminating the landscape of Vesta during a Vestan ‘sunrise’. When this image was obtained the sun had a low angle relative to Vesta’s surface, just as the sun has a low angle in the sky in the morning on Earth. This ‘early morning’, low angle light on Vesta enhances the surface topography of the illuminated regions. For example, the morphological details of the interior wall of the crater in the bottom right of the image are especially clear. Also, the clusters and chains of pits in the center of the image are also enhanced by this sunlight. These clusters and chains of pits were created by material ejected by an impact outside of the imaged area. However, there are many regions that are still in shadow in this image because the low angled sunlight has not illuminated them.

17.02.2012 - Impact ejecta deposits covering underlying topography

This Dawn FC (framing camera) image shows impact ejecta deposits dominating Vesta’s landscape. This impact ejecta material was ejected from an impact crater located outside the imaged area. When this fine-grained ejecta was deposited on Vesta’s surface the underlying topography was smoothed out, which results in the subdued and blurred appearance of the landscape in this image. Large, house-sized boulders are scattered across the surface and these are especially clear in the lower right part of the image. Large boulders such as these are also frequently ejected as impact craters form. Some younger, fresher impact craters have been superimposed onto the ejecta deposits and are visible across the image.

16.02.2012 - Successive formation of impact craters

This Dawn FC (framing camera) image shows two overlapping impact craters. The large crater is roughly 20 kilometers (12 miles) in diameter and the smaller crater is roughly 6 kilometers (4 miles) in diameter. The rims of the craters are both reasonably fresh but the larger crater must be older because the smaller crater cuts across the larger crater’s rim. As the smaller crater formed it destroyed a part of the rim of the pre-existing, larger crater. The larger crater’s interior is more densely cratered than the smaller crater, which also suggests that is it older. In the bottom of the image there is some material slumping from rim of the larger crater towards its center.

15.02.2012 - Mass wasting on steep slopes

This Dawn FC (framing camera) image shows many highly degraded craters in the top part of the image. These craters are roughly 4 kilometers (3 miles) in diameter and are so degraded that their rims are only partially visible. They are highly degraded because material has been lost down the steep slope below them. Downslope movement of material such as this is called mass wasting. The mass wasted material in this image is relatively smooth and is located on the slope that runs roughly horizontally across the image. The mass wasted material is sparsely cratered, unlike the other areas visible in the image. Mass wasting happens on steep slopes, which can occur along the sides of elongate depressions, called graben, and on the sides of craters.

14.02.2012 - A Valentine from Vesta

This image is based on a Dawn FC (framing camera) image that is overlain by a color-coded height representation of topography. The topography is calculated from a set of images that were observed from different viewing directions, which allows stereo reconstruction. The various colors correspond to the height of the area. The white and red areas in the top of the image are the highest areas and the blue, heart-shaped area in the bottom of the image is the lowest area. This heart-shaped hollow is roughly 10 kilometers (6 miles) across at its widest point.

13.02.2012 - Vesta’s surface at high resolution: dominated by impact craters

In this Dawn FC (framing camera) image a large number of craters, formed by collisions into the surface of Vesta, are visible. The craters in this image range in diameter from less than 1 kilometer (0.6 mile) to approximately 4 kilometers (2.5 miles). Whether you are looking at a high-resolution or a low-resolution image, various types of impact craters dominate Vesta’s surface. The relatively large circular depressions in this image are older, heavily degraded impact craters. The craters with sharper rims are fresher craters. Clusters of small secondary craters were created by the impact of material and boulders that were ejected when larger primary craters formed.

10.02.2012 - Markings of ejected material on Vesta’s surface

This Dawn FC (framing camera) image shows many linear or sinuous grooves crisscrossing the surface of Vesta. These grooves are less than 1 kilometer (0.6 mile) in width. They were created when large pieces of debris, which were ejected when material from space hit Vesta, grazed and scoured the surface. The large, circular depressions in this image are old, heavily degraded craters whose rims are barely visible. These heavily degraded craters have been almost completely filled up by material called regolith. Regolith consists of numerous small particles that were deposited or created by various impacts into Vesta.

09.02.2012 - Chains and clusters of secondary craters

This Dawn FC (framing camera) image shows numerous linear chains and clusters of small craters. These chains and clusters of craters were created by material that was ejected during the formation of a larger crater, which is located far outside of this image. These craters are called secondary craters because they are formed by material ejected from a primary impact of material from space. There is a large crater in shadow at the top left of the image. The chains and clusters do not originate from this crater because there are not orientated radially to it, as if they were ejected from the crater.

08.02.2012 - Mosaic of visible and infrared spectrometer data

This mosaic shows the location of the data acquired by VIR (visible and infrared spectrometer) during the HAMO (high-altitude mapping orbit) phase of the Dawn mission. VIR can image Vesta in a number of different wavelengths of light, ranging from the visible to the infrared part of the electromagnetic spectrum. This mosaic shows the images taken at a wavelength of 550 nanometers, which is in the visible part of the electromagnetic spectrum. During HAMO VIR obtained more than 4.6 million spectra of Vesta. It is clear from this image that the VIR observations are widely distributed across Vesta, which results in a global view of the spectral properties of Vesta’s surface.

07.02.2012 - Small-scale surface variations seen with Dawn’s visible and infrared spectrometer

This image shows a Dawn VIR (visible and infrared spectrometer) image, overlain on top of a FC (framing camera) image of the same region. The VIR image was acquired during the HAMO (high-altitude mapping orbit) phase of the Dawn mission and the FC image was acquired during the Survey phase of the mission. The small-scale brightness and darkness variations in this image demonstrate VIR’s ability to detect small-scale features on Vesta’s surface. The composition of these various features can then be analyzed. VIR data have shown that, in general, Vesta has a basaltic surface and that two prominent pyroxene absorption bands dominate Vesta’s spectrum.

06.02.2012 - Undulating terrain in Vesta’s southern hemisphere

This Dawn FC (framing camera) image shows the undulating terrain of Vesta’s southern hemisphere, which consists of ridges and depressions. This undulating terrain is only located in Vesta’s southern hemisphere, in and around the Rheasilvia impact basin. Many of these linear, curving ridges and depressions are clear in the left side of the image. A single ridge can continue for many tens of kilometers and the spacing between ridges is generally less than 10 kilometers (6 miles). There are some craters superposed onto these ridges and depressions. Also, many linear, curving grooves cut across the undulating terrain. These grooves are orientated in various directions throughout the image.

03.02.2012 - Ejecta and dark rayed crater

This Dawn FC (framing camera) image shows part of the ejecta deposit surrounding the ‘Snowman’ craters, the largest of which has been named Marcia. Ejecta deposits consist of small debris thrown out of craters that are formed by an impact. Because they are made of small debris ejecta deposits commonly have a smooth appearance. The ejecta also has a bubbly texture and some smaller, younger craters superposed onto it. In the bottom right part of the image there is a roughly 2 kilometer (1 mile) diameter crater with dark rays of ejecta extending out from it. These rays have an impressive range of roughly 10 kilometers (6 miles).

02.02.2012 - Old cratered terrain on Vesta’s equator

This Dawn FC (framing camera) image shows old cratered terrain located on Vesta’s equator. Many of these craters have very degraded, rounded rims. There is a large crater near the top center of the image, which has such a degraded rim that it is only visible as a shallow depression. There are three smaller, fresher craters located across the rim of this crater. Unlike many areas on Vesta’s surface, very few of these craters have any bright or dark material exposed in them. However, there are many grooves crisscrossing many of the craters. These grooves are orientated in two different diagonal directions across the image.

01.02.2012 - Undulating terrain in Vesta’s southern hemisphere

This Dawn FC (framing camera) image shows some of the undulating terrain in Vesta’s southern hemisphere. This undulating terrain consists of linear, curving hills and depressions, which are most distinct in the right of the image. Many narrow, linear grooves run in various directions across this undulating terrain. There are some small, less than 1 kilometer (0.6 mile) diameter, craters in the bottom of the image. These contain bright material and have bright material surrounding them. There are fewer craters in this image than in images from Vesta’s northern hemisphere; this is because Vesta’s northern hemisphere is generally more cratered than the southern hemisphere.

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