Draft:Original research/Vesta

In the full image of Vesta at right, the rocky-object appears to have suffered from meteor damage.

Astronomy
Vesta (minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of 525 km.
 * diameter= 530 kilometres
 * features= Veneneia basin

Vesta's rotation is relatively fast for an asteroid (5.342 h) and prograde, with the north pole pointing in the direction of right ascension 20 h 32 min, declination +48° (in the constellation Cygnus) with an uncertainty of about 10°, provides an axial tilt of 29°.

Planetary sciences
Def. an "astronomical object in direct orbit around the Sun (star) [or another star] smaller than a planet and not classified as a comet. " is called a minor planet.

Def. is called a planetoid.
 * 1) an "asteroid of any size" ,
 * 2) an "asteroid-like body in an orbit beyond the asteroid belt" ,
 * 3) a "larger, planetary, body in orbit around the Sun]", or other star, or
 * 4) a "dwarf planet" ,

Usage notes: "The term "planetoid" has never been precisely defined. At first, it was a synonym for asteroid; whereas "asteroid" referred to the star-like image seen through a telescope, "planetoid" referred to its planet-like orbit. Though it approached the popularity of "asteroid" ca. 1915, this usage was never dominant, and largely ceased by ca. 1980. Even before then the etymology of the term was reanalyzed as meaning planet-like in form, and started being used for larger asteroids such as Vesta which had planet-like geologies (that is, were planetary bodies). There was an increase in such usage after 2000 with the discovery of planetary bodies in the Kuiper belt and beyond, which many felt were not appropriately called "asteroids" and concomitant with doubts as to the appropriate definition of "planet". Sedna, for example, was called a "planetoid" in its discovery announcement."

"The group of small bodies that circle round the Sun, outside the orbit of Mars, are known under the designation of the planetoids." Bold added.

For a model on the generation of chondrites, "if one can argue for the early existence of a few largely molten planetoids with dimension of kilometers or tens of kilometers, one can quite as easily argue for very large numbers of such planetoids."

Def. any "of many small, solid astronomical objects, that orbit a star and form protoplanets through mutual gravitational attraction" is called a planetesimal.

Vesta is the second-most-massive and probably the second-largest asteroid, after the dwarf planet Ceres,  and contributes an estimated 9% of the mass of the asteroid belt. It is probably slightly larger than 2 Pallas, but is about 25% more massive. Vesta is the only known remaining rocky protoplanet (with a Planetary differentiation) of the kind that formed the terrestrial planets. Numerous fragments of Vesta were ejected by collisions one and two billion years ago that left two enormous craters occupying much of Vesta's southern hemisphere. Debris from these events has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, which have been a rich source of information about Vesta.

Minerals
"High precision spectrophotometry of 4 Vesta, the third largest asteroid, was used to establish the surface composition of this body and to investigate mineralogical variations across its surface."

"The average surface of Vesta is analogous to howardite and/or polymict eucrite assemblages, regolith-derived members of the HED meteorite suite which consist of a eucrite matrix containing differing amounts of a diogenite component."

"Color and/or spectral changes, which exhibit a consistent relationship to rotational phasing, are evident in 16 of 18 studies of Vesta dating back to 1929, including the present work. After elimination of possible sources of spurious spectral or color changes, it is concluded that these variations arise from hemispheric variations in surface materials, and hence provide a means of spatially resolving subhemispheric compositional units on the surface of Vesta."

"The background surface of Vesta is a relatively dark howardite or polymict eucrite (pyroxene–plagioclase) assemblage with several compositionally distinct bright regions clustered in one hemisphere viewed around the maximum in Vesta's lightcurve. These include what appears to be an olivine-bearing unit (suggested name “Leslie Formation”) located near Vesta's equator which probably represents an impact basin (and/or its associated ejecta) that penetrated through the basaltic crust. Other high-albedo compositional units including an apparently low-calcium eucrite region and several diogenite (pyroxenite) regions, at least one located near the southern pole, may be smaller, shallower impact basins."

"By analogy to the eucrite meteorites, which represent surface flows or shallow intrusions and which constitute the major component of the regolith-derived howardites and polymict eucrites, [...] the howardite/polymict eucrite units represent a regolith-gardened original surface of Vesta. It is probable that the low albedo of the background surface on Vesta is due to an age-related darkening effect similar to that inferred from the Galileo images of Gaspra and Ida. This mechanism is consistent with the correlation of absorption feature intensity with the lightcurve. Vesta appears to have an old eucritic surface, darkened with age and represented among the meteorites by the regolith-derived howardites and polymict eucrites, on which several impacts on one hemisphere have exposed fresher brighter diogenite and olivine-bearing material."

"Based on qualitative analysis of the mineralogical variations as a function of rotation, a generalized lithologic map of Vesta was produced. There is reasonable control on the longitude of lithologic features but little control on their latitudes, except where specifically noted. In producing this map, discrete circular features were used on the plausible assumption that impacts have been the most important geologic process on this surface for most of the age of the solar system. The shape of the features has thus been assumed rather than derived and is subject to future revision as data improve."

Theory of Vesta
Def. "[the] fourth asteroid discovered" is called Vesta, or 4 Vesta.

Vesta may have been melted 4.5 mya and it is believed to once have volcanic activity. Smaller asteroids may have deposited carbon material to Vesta, contrasting its bright color.

Vesta doesn't have enough gravity to form it into a complete sphere, which is why it is not a dwarf planet.

This anaglyph [of Vesta at right] -- best viewed through red-blue glasses -- shows a 3-D model of the protoplanet Vesta, using scientists' best guess to date of what the surface of the protoplanet might look like. It was created as part of an exercise for NASA's Dawn mission involving mission planners at NASA's Jet Propulsion Laboratory and science team members at the Planetary Science Institute in Tuscon, Ariz.

The images incorporate the best data on dimples and bulges of the protoplanet Vesta from ground-based telescopes and NASA's Hubble Space Telescope. The cratering and small-scale surface variations are computer-generated, based on the patterns seen on the Earth's moon, an inner solar system object with a surface appearance that may be similar to Vesta.

Vesta, located in the main asteroid belt between Mars and Jupiter, formed very early in the history of the solar system and has one of the oldest surfaces in the system. Scientists are eager to get their first close-up look so they can better understand this early chapter.

Meteors
"It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid.

Neutrons
"Using Dawn’s Gamma Ray and Neutron Detector, ... Global Fe/O and Fe/Si ratios are consistent with [howardite, eucrite, and diogenite] HED [meteorite] compositions."

Opticals
"NASA's Dawn spacecraft obtained [the] image [at right] with its framing camera on July 9, 2011. It was taken from a distance of about 26,000 miles (41,000 kilometers) away from the protoplanet Vesta. Each pixel in the image corresponds to roughly 2.4 miles (3.8 kilometers)."

Visuals
The angular resolution of the naked eye is about 1&prime;; however, some people have sharper vision than that. There is anecdotal evidence that people had seen the Galilean moons of Jupiter before telescopes were invented. Of similar magnitude, Uranus and Vesta had most probably been seen but could not be recognized as planets because they appear so faint even at maximum brightness that their motion could not be detected.

Oranges
"The [NASA's Dawn spacecraft] Framing Camera (FC) discovered enigmatic orange material on Vesta. FC images revealed diffuse orange ejecta around two impact craters, 34-km diameter Oppis, and 30-km diameter Octavia, as well as numerous sharp-edge orange units in the equatorial region." The spacecraft "entered orbit around asteroid (4) Vesta in July 2011 for a year-long mapping orbit."

Reds
"To prepare for the Dawn spacecraft's visit to Vesta, astronomers used Hubble's Wide Field Planetary Camera 2 to snap new images of the asteroid. The image at right was taken on May 14 and 16, 2007. Using Hubble, astronomers mapped Vesta's southern hemisphere, a region dominated by a giant impact crater formed by a collision billions of years ago. The crater is 285 miles (456 kilometers) across, which is nearly equal to Vesta's 330-mile (530-kilometer) diameter. If Earth had a crater of proportional size, it would fill the Pacific Ocean basin. The impact broke off chunks of rock, producing more than 50 smaller asteroids that astronomers have nicknamed "vestoids." The collision also may have blasted through Vesta's crust. Vesta is about the size of Arizona."

"Previous Hubble images of Vesta's southern hemisphere were taken in 1994 and 1996 with the wide-field camera. In this new set of images, Hubble's sharp "eye" can see features as small as about 37 miles (60 kilometers) across. The image shows the difference in brightness and color on the asteroid's surface. These characteristics hint at the large-scale features that the Dawn spacecraft [sees] when it arrives at Vesta."

"Hubble's view reveals extensive global features stretching longitudinally from the northern hemisphere to the southern hemisphere. The image also shows widespread differences in brightness in the east and west, which probably reflects compositional changes. Both of these characteristics could reveal volcanic activity throughout Vesta. The size of these different regions varies. Some are hundreds of miles across."

"The brightness differences could be similar to the effect seen on the Moon, where smooth, dark regions are more iron-rich than the brighter highlands that contain minerals richer in calcium and aluminum. When Vesta was forming 4.5 billion years ago, it was heated to the melting temperatures of rock. This heating allowed heavier material to sink to Vesta's center and lighter minerals to rise to the surface."

"Astronomers combined images of Vesta in two colors to study the variations in iron-bearing minerals. From these minerals, they hope to learn more about Vesta's surface structure and composition."

"The simplest model for the genesis of the HED meteorites involves a series of partial melting and crystallization events [1] of a small parent body whose bulk composition is more or less consistent with cosmic abundances but is depleted in the moderately volatile elements Na and K [2]."

"Why should both Vesta and the Moon be rich in oxidized Fe but depleted in Na and K?"

"How did the HEDs get here from Vesta? The discovery of a string of Vesta-like asteroids in orbits linking Vesta to nearby orbital resonances [5] has shown that [...] arguments [...] for material originating at Vesta to reach Earth-crossing orbits are [...] valid."

"An alternative theory is based on electromagnetic heating during an episode of strong solar wind from the early proto-Sun when our star experienced a T Tauri phase, as predicted by modern stellar astrophysics."

Meteorites
An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies. As a result, achondrites have distinct textures and mineralogies indicative of igneous processes.

"Achondrites account for about 8% of meteorites overall, and the majority (about two thirds) of them are HED meteorites, originating from the crust of asteroid 4 Vesta. Other types include Martian, Lunar, and several types thought to originate from as-yet unidentified asteroids other than Vesta. These groups have been determined on the basis of e.g. the Fe/Mn chemical ratio and the 17O/18O oxygen isotope ratios, thought to be characteristic "fingerprints" for each parent body.

"Debris from [a meteor collison with Vesta] has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid.

Micrometeorite is often abbreviated as MM. Most MMs are broadly chondritic in composition, meaning "that major elemental abundance ratios are within about 50% of those observed in carbonaceous chondrites." Some MMs are chondrites, (basaltic) howardite, eucrite, and diogenite (HED) meteorites or Martian basalts, but not lunar samples. "[T]he comparative mechanical weakness of carbonaceous precursor materials tends to encourage spherule formation." From the number of different asteroidal precursors, the approximate fraction in MMs is 70 % carbonaceous. "[T]he carbonaceous material [is] known from observation to dominate the terrestrial MM flux." The "H, L, and E chondritic compositions" are "dominant among meteorites but rare among micrometeorites."

"Ureilites occur about half as often as eucrites (Krot et al. 2003), are relatively friable, have less a wide range of cosmic-ray exposure ages including two less than 1 Myr, and, like the dominant group of MM precursors, contain carbon."

Howardite–eucrite–diogenite meteorites
Def. an "achondritic stony meteorite originating from deep within the crust of the asteroid 4 Vesta" is called a diogenite.

Def. an "achondritic meteoritic rock consisting chiefly of pigeonite and anorthite" is called a eucrite.

The eucrite specimen at left is approximately 6 cm wide. Note the shiny black fusion crust with flow lines. The chip at lower right allows one to see the light-gray interior. The orange staining at top is a result of weathering, as these stones were not recovered until many years after they fell.

Def. an "achondritic stony meteorite" is called a howardite.

"Approximately 1,700 HED meteorites have been identified in the meteorite collections; however, high-pressure minerals have only been reported in one shocked eucrite18."

Diogenites
Diogenites are composed of igneous rocks of plutonic origin, having solidified slowly enough deep within Vesta's crust to form crystals which are larger than in the eucrites, which are primarily magnesium-rich orthopyroxene (enstatite), with small amounts of plagioclase and olivine.

"The remaining six are interpreted as diogenitic in composition and were designated as J asteroids (mnemonic for the Johnstown diogenite)."

Eucrites


The eucrite specimen at top right is approximately 6 cm wide. Note the shiny black fusion crust with flow lines. The chip at lower right allows one to see the light-gray interior. The orange staining at top is a result of weathering, as these stones were not recovered until many years after they fell.

Eucrites consist of basaltic rock from the crust of 4 Vesta or a similar parent body, mostly composed of Ca-poor pyroxene, pigeonite, and Ca-rich plagioclase (anorthite).

Howardites
"High precision spectrophotometry of 4 Vesta, the third largest asteroid, was used to establish the surface composition of this body and to investigate mineralogical variations across its surface."

"The average surface of Vesta is analogous to howardite and/or polymict eucrite assemblages, regolith-derived members of the HED meteorite suite which consist of a eucrite matrix containing differing amounts of a diogenite component."

"Color and/or spectral changes, which exhibit a consistent relationship to rotational phasing, are evident in 16 of 18 studies of Vesta dating back to 1929, including the present work. After elimination of possible sources of spurious spectral or color changes, it is concluded that these variations arise from hemispheric variations in surface materials, and hence provide a means of spatially resolving subhemispheric compositional units on the surface of Vesta."

"The background surface of Vesta is a relatively dark howardite or polymict eucrite (pyroxene–plagioclase) assemblage with several compositionally distinct bright regions clustered in one hemisphere viewed around the maximum in Vesta's lightcurve. These include what appears to be an olivine-bearing unit (suggested name “Leslie Formation”) located near Vesta's equator which probably represents an impact basin (and/or its associated ejecta) that penetrated through the basaltic crust. Other high-albedo compositional units including an apparently low-calcium eucrite region and several diogenite (pyroxenite) regions, at least one located near the southern pole, may be smaller, shallower impact basins."

"By analogy to the eucrite meteorites, which represent surface flows or shallow intrusions and which constitute the major component of the regolith-derived howardites and polymict eucrites, [...] the howardite/polymict eucrite units represent a regolith-gardened original surface of Vesta. It is probable that the low albedo of the background surface on Vesta is due to an age-related darkening effect similar to that inferred from the Galileo images of Gaspra and Ida. This mechanism is consistent with the correlation of absorption feature intensity with the lightcurve. Vesta appears to have an old eucritic surface, darkened with age and represented among the meteorites by the regolith-derived howardites and polymict eucrites, on which several impacts on one hemisphere have exposed fresher brighter diogenite and olivine-bearing material."

"Based on qualitative analysis of the mineralogical variations as a function of rotation, a generalized lithologic map of Vesta was produced. There is reasonable control on the longitude of lithologic features but little control on their latitudes, except where specifically noted. In producing this map, discrete circular features were used on the plausible assumption that impacts have been the most important geologic process on this surface for most of the age of the solar system. The shape of the features has thus been assumed rather than derived and is subject to future revision as data improve."

Asteroids
Vesta, minor-planet designation 4 Vesta, is one of the largest asteroids in the Solar System.

V asteroids
In the full image of Vesta at right, the rocky-object appears to have suffered from meteor damage.

Vesta, minor-planet designation 4 Vesta, is one of the largest asteroids in the Solar System. It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid.

"V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta."

The Vestian asteroids consist "of 4 Vesta, the second-most-massive of all asteroids (mean diameter of 530 km), and many small asteroids below 10 km diameter. The brightest of these, 1929 Kollaa and 2045 Peking, have an absolute magnitude of 12.2, which would give them a radius of about 7.5 km assuming the same high albedo as 4 Vesta."

"A HCM numerical analysis (by Zappala 1995) determined a large group of 'core' family members, whose proper orbital elements lie in the approximate ranges"

"This gives the approximate boundaries of the family. At the present epoch, the range of  osculating orbital elements of these core members is"

"The Zappala 1995 analysis found 235 core members. A search of a recent proper-element database (AstDys) for 96944 minor planets in 2005 yielded 6051 objects (about 6% of the total) lying within the Vesta-family region as per the first table above."

Hestiomorphology
Vesta's surface is covered by regolith distinct from that found on the Moon or asteroids such as 25143 Itokawa. This is because space weathering acts differently. Vesta's surface shows no significant trace of nanophase iron because the impact speeds on Vesta are too low to make rock melting and vaporization an appreciable process. Instead, regolith evolution is dominated by brecciation and subsequent mixing of bright and dark components. The dark component is probably due to the infall of carbonaceous material, whereas the bright component is the original Vesta basaltic soil.

Compositional information from the visible and infrared spectrometer (VIR), gamma-ray and neutron detector (GRaND), and framing camera (FC), all indicate that the majority of the surface composition of Vesta is consistent with the composition of the howardite, eucrite, and diogenite meteorites. The Rheasilvia region is richest in diogenite, consistent with the Rheasilvia-forming impact excavating material from deeper within Vesta. The presence of olivine within the Rheasilvia region would also be consistent with excavation of mantle material. However, olivine has only been detected in localized regions of the northern hemisphere, not within Rheasilvia. The origin of this olivine is currently unknown.

Circular structures
The circular structure appears to be a set of roughly concentric troughs or ripples crossed by approximately radial ridges at or around Vesta's South Pole.

Craters
On the right, Feralia Planitia, an old, degraded crater is near the equator of Vesta (green and blue). It is 270 kilometers (168 mi) long and precedes the crater Rheasilvia (green at the bottom). The "snowman craters" is an informal name given to a group of three adjacent craters in Vesta's northern hemisphere. Their official names from largest to smallest (west to east) are Marcia, Calpurnia, and Minucia. Marcia is the youngest and cross-cuts Calpurnia. Minucia is the oldest. These Dawn framing camera (FC) images of Vesta show Claudia crater at both HAMO (high-altitude mapping orbit) and LAMO (low-altitude mapping orbit) resolutions. The left image is the HAMO image and the right image is the LAMO image. To find Claudia crater use the two relatively large degraded craters that form the figure of eight shape in the bottom left of the LAMO image. On the middle right rim of these craters there is a small crater. About 3 kilometers (1.9 miles) to the bottom right of this crater is Claudia, which is 0.7 kilometers (0.4 miles) in diameter. The LAMO image is approximately three times better spatial resolution than the HAMO image. In images with higher spatial resolutions smaller objects can be better distinguished. Claudia was chosen to anchor the coordinate system for Vesta that is used in the scientific investigations of the Dawn team. Claudia was chosen for this because it is a small crater, which is reasonably easy to find, near Vesta’s equator.

These images are located in Vesta’s Oppia quadrangle, just south of Vesta’s equator. NASA’s Dawn spacecraft obtained the left image with its framing camera on Oct. 25, 2011. This image was taken through the camera’s clear filter. The distance to the surface of Vesta is 700 kilometers (435 miles) and the image has a resolution of about 63 meters (207 feet) per pixel. This image was acquired during the HAMO (high-altitude mapping orbit) phase of the mission. NASA’s Dawn spacecraft obtained the right image with its framing camera on April 1, 2012. This image was taken through the camera’s clear filter. The distance to the surface of Vesta is 272 kilometers (169 miles) and the image has a resolution of about 19 meters (62 feet) per pixel. This image was acquired during the LAMO (low-altitude mapping orbit) phase of the mission.

This colorful composite image from NASA's Dawn mission shows the flow of material inside and outside a crater called Aelia on the giant asteroid Vesta. The area is around 14 degrees south latitude. The images that went into this composite were obtained by Dawn's framing camera from September to October 2011.

To the naked eye, these structures would not be seen. But here, they stand out in blue and red. The crater has a diameter of 2.7 miles (4.3 kilometers). The exact origin of the flow structures is unknown. A possible explanation is that the impact that produced the crater could have created liquid material with different minerals than the surroundings.

The composite image was created by assigning ratios of color information collected from several color filters in visible light and near-infrared light to maximize subtle differences in lithology (the physical characteristics of rock units, such as color, texture and composition). The color scheme pays special attention to the iron-rich mineral pyroxene.

Pitted terrains
Pitted terrain has been observed in four craters on Vesta: Marcia, Cornelia, Numisia and Licinia. The formation of the pitted terrain is proposed to be degassing of impact-heated volatile-bearing material. Along with the pitted terrain, curvilinear gullies are found in Marcia and Cornelia craters. The curvilinear gullies end in lobate deposits, which are sometimes covered by pitted terrain, and are proposed to form by the transient flow of liquid water after buried deposits of ice were melted by the heat of the impacts. Hydrated materials have also been detected, many of which are associated with areas of dark material. Consequently, dark material is thought to be largely composed of carbonaceous chondrite, which was deposited on the surface by impacts. Carbonaceous chondrites are comparatively rich in mineralogically bound OH.

Poles
This image from NASA's Dawn mission shows the topography of the northern and southern hemispheres of the giant asteroid Vesta, updated with pictures obtained during Dawn's last look back. Around the time of Dawn's departure from Vesta in the late summer of 2012, dawn was beginning to creep over the high northern latitudes, which were dark when Dawn arrived in the summer of 2011.

These color-shaded relief maps show the northern and southern hemispheres of Vesta, derived from images analysis. Colors represent distance relative to Vesta's center, with lows in violet and highs in red. In the northern hemisphere map on the left, the surface ranges from lows of minus 13.82 miles (22.24 kilometers) to highs of 27.48 miles (44.22 kilometers). Light reflected off the walls of some shadowed craters at the north pole (in the center of the image) was used to determine the height. In the southern hemisphere map on the right, the surface ranges from lows of minus 23.65 miles (38.06 kilometers) to 26.61 miles (42.82 kilometers).

The shape model was constructed using images from Dawn's framing camera that were obtained from July 17, 2011, to Aug. 26, 2012. The data have been stereographically projected on a 300-mile-diameter (500-kilometer-diameter) sphere with the poles at the center.

The three craters that make up Dawn's "snowman" feature can be seen at the top of the northern hemisphere map on the left. A mountain more than twice the height of Mount Everest, inside the largest impact basin on Vesta, can be seen near the center of the southern hemisphere map on the right.

Troughs
Apparent brightness and topography images of Divalia Fossa and Rubria and Occia craters are shown. 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. These images show a part of the large trough, Divalia Fossa, which encircles most of Vesta’s equator. Divalia Fossa is visible in both the apparent brightness image and the topography image: it is the approximately 10 kilometer (6 mile) wide depression that runs from the left corner to the right corner of the images. The top rim of Divalia Fossa is especially clear in the topography image. A number of smaller troughs above and below Divalia Fossa are parallel to it. Rubria and Occia craters straddle Divalia Fossa: Rubria is the crater with dark and bright material above Divalia Fossa and Occia is the crater with bright and dark material below.

These images are located in Vesta’s Gegania quadrangle, just south of Vesta’s equator. NASA’s Dawn spacecraft obtained the apparent brightness image with its framing camera on Oct. 16, 2011. This image was taken through the camera’s clear filter. The distance to the surface of Vesta is 700 kilometers (435 miles) and the image has a resolution of about 70 meters (230 feet) per pixel. This image was acquired during the HAMO (high-altitude mapping orbit) phase of the mission. These images are lambert-azimuthalmap projected.

As Dawn sent the first close-up images of Vesta back to Earth in July 2011, scientists immediately noticed numerous grooves, as if created by a gigantic plow. This image shows two grooves in the Divalia Fossa system, running parallel to the lower edge of the image.

The majority of these grooves extend along the equator, but a second group -- inclined with respect to the equator -- have been identified in the northern hemisphere. These parallel trenches are usually several hundred miles (kilometers) long, up to 9 miles (15 kilometers) wide and more than a half mile (1 kilometer) deep. They are the result of two large asteroid impacts far in the southern hemisphere, demonstrating that impact events that occurred hundreds of miles (kilometers) apart caused shocks throughout Vesta and altered its surface.

The scene is an artificially generated oblique view of the grooves (or troughs) that run along Vesta's equator. The image was rendered from a global mosaic of Vesta processed from thousands of individual images obtained by the framing camera between January and April 2012. The altitude was approximately 130 miles (210 kilometers) above Vesta's surface. The image resolution is about 70 feet (20 meters) per pixel.

Geologic maps
This high-resolution geological map of Vesta is derived from Dawn spacecraft data. Brown colors represent the oldest, most heavily cratered surface. Purple colors in the north and light blue represent terrains modified by the Veneneia and Rheasilvia impacts, respectively. Light purples and dark blue colors below the equator represent the interior of the Rheasilvia and Veneneia basins. Greens and yellows represent relatively young landslides or other downhill movement and crater impact materials, respectively. This map unifies 15 individual quadrangle maps published this week in a special issue of Icarus. Map is a Mollweide projection, centered on 180 degrees longitude using the Dawn Claudia coordinate system.

Exploratory rocketry
The Visible and IR spectrometer is able to make pictures of the core in the IR and also search for IR spectra of molecules in the coma. The detection is done by a mercury cadmium teluride array for IR and with a CCD chip for the Visible range. Improved versions were used for Dawn and Venus express.

The Dawn spacecraft has onboard a framing camera (FC) with a refractive optical system and an 8-position filter wheel of a panchromatic (clear filter) and seven narrow band filters. The visual and infrared spectrometer (VIR) has an array of HgCdTe photodiodes cooled to about 70K spans the spectrum from 0.95 to 5.0 µm. The green filter aboard Dawn in the FC has a central wavelength of 555 nm. The VIR on Dawn has a green filter centered at 563 nm.

Hypotheses

 * 1) If most of the asteroids in the asteroid belt are spheroidal, then the belt is much older than it appears.