(4) Vesta

Template: Infobox Asteroid / Maintenance / Error 1

Vesta or - in the nomenclature for asteroids - (4 ) Vesta is about 516 km average diameter of the second largest asteroid and third largest celestial bodies in the main asteroid belt. In mass it is only from the dwarf planet ( 1) Ceres exceeded.

Discovery

Vesta was discovered on March 29, 1807 by Heinrich Wilhelm Olbers in Bremen as the fourth asteroid. After Olbers had in 1802 already discovered and named Pallas, he transferred the right of naming time to Carl Friedrich Gauss, who had contributed with his new method of orbit determination crucial for securing the newly discovered asteroid. Gauss called the celestial body after Vesta, the Roman goddess of hearth and home and sister of Ceres.

As of 1801 discovered dwarf planet Ceres and the 1802 and 1804 discovered asteroid Pallas, Juno and Vesta was initially referred to as a planet. As to the discovery of Astraea still should take more than 38 years, it changed nothing at first. It was not until after about 1850, the number of celestial bodies found between the orbits of the planets Mars and Jupiter rising rapidly, uphold these objects, the terms " Tiny Planets ", " minor planet ", " planetoid " or " asteroids " by.

Orbit

Vesta moves between 2.15 AU ( perihelion ) and 2.57 AU ( aphelion ) in 3.63 years of the sun. Your orbit is inclined 7.1 ° to the ecliptic, the orbital eccentricity is 0.089. Your web is therefore in the inner asteroid belt.

The synodic period of Vesta is 504 days.

Nature

Size and brightness

The shape of Vesta corresponds to a triaxial ellipsoid with radii of 280 km, 272 km and 227 km (± 12 km). For the mass, a value of 1.36 (± 0.05 ) x 10-10 sun mass (2.71 × 1020 kg ) and an average density of 3.7 (± 0.3 ) g / cm 3 has been published. The rotation period of the asteroid is about 5.3 hours.

Vesta has compared to other asteroids a relatively bright surface with an albedo of 0.42. While the opposition is removed between 1.14 AU and 1.59 AU from the Earth, reaching an apparent magnitude of up to 5.2 mag. This makes it the brightest asteroid in the night sky and can be seen just yet with the naked eye under dark skies without light pollution.

Composition and surface

Vesta is a differentiated asteroid with a basaltic crust, ultramafic mantle rock, and, as can be concluded from the average density, an iron - nickel core. Thus, Vesta has a structure similar to the terrestrial planets and differs from all other asteroids in the main belt. However, the iron meteorites found on Earth lead to the conclusion that there must have been in the early days of the solar system more differentiated planetesimals that were apparently destroyed by collisions, because the iron meteorites are interpreted as fragments of metallic cores of these objects.

Also Vesta must have suffered severe collisions with other massive bodies. So on images from the Hubble Space Telescope beside several impact craters with diameters up to 150 km to recognize an exceptional big crater with a diameter of about 450 km. This crater has a depth of 8 km ( adjacent figure coded blue ), its walls are additionally between 8 km and 14 km high, and at its center stands a central mountain 13 km high on (shown in red).

With the help of the Hubble Space Telescope, not only the shape and size of Vesta could be determined, but it could be detected on the surface also bright and dark regions, even a geological map could be created. The surface seems to consist entirely of igneous rocks. The green regions shown in the geological map are interpreted as solidified basalt lava flows and thus to provide remnants of the original surface of Vesta represents the red -coded areas thought to consist of intrusive rocks that initially cooled down below the surface, but were later exposed by impacts.

The geological activity of Vesta is probably due to the released during the radioactive decay of aluminum isotope 26Al heat and likely before about 4.4 billion years, so relatively soon after the formation of the solar system about 4.55 billion years ago, back to a standstill have come.

Spectroscopic observations at the Mauna Kea Observatory have shown that on the surface of Vesta, small amounts of water or hydroxide-containing minerals exist. It is assumed that this material was applied after cooling the asteroids on impact of comets or carbonaceous chondrites.

Meteorites and Vestoids

Probably Vesta is also the parent body of the meteorites of the HED group ( Howardites, eucrites, diogenites ), which form a subset of the achondrites and are similar to the terrestrial igneous rocks. The connection between the HED meteorites and Vesta was made because the spectra of these meteorites and asteroids of the same. This assignment is supported by the fact that all investigated HED meteorites have an age from 4.4 to 4.5 billion years ago. The parent bodies of these meteorites cooled so after the formation of the solar system rapidly, indicating a relatively small celestial bodies and excludes an origin from larger moons or planets.

With Vesta also Vestoids be associated, a class of smaller asteroids, which also exhibit spectral similarities with Vesta and may have been knocked off by this. Probably the Vestoids were knocked out less than a billion years at that strike from the crust of Vesta, who formed the great crater described above. The distribution of Vestoids extends from the orbit of Vesta, to regions in the asteroid belt, subject to the interference caused by the planet Jupiter. Thus, fragments of Vesta could be to Earth's orbit cruisers, and HED meteorites could thus have been brought into the vicinity of the earth. Whether they come directly from Vesta or indirectly via a Vestoids, but is still unclear.

Exploration by the Dawn spacecraft

Vesta was the first goal of the Dawn spacecraft, which was launched on September 27, 2007. On 15 July 2011, the probe swung into orbit around Vesta. For images that were drawn between July and August 2011, during the approach, as well as from a height of 2700 km, the research group led by Ralf Jaumann of the German Aerospace Center (DLR ) created a 3D video. During the virtual overflight can be seen at the south pole of a mountain about 25 km altitude, which is almost three times higher than Mount Everest. Dawn explored the planetoid to 5 September 2012, and since then flies to Ceres further that should they reach the beginning of 2015. One expects this mission to Vesta and characterize their relationship to meteorites. A comparison of Vesta with the carbonaceous asteroids in the outer asteroid belt, which are represented by the dwarf planet Ceres, will be possible.

Vesta from 100,000 kilometers, July 1, 2011

Vesta from 41,000 kilometers, July 9, 2011

First image from orbit 16,000 kilometers in distance 17 July, 2011

Nomenclature

According to IAU nomenclature structures on Vesta are named as follows:

  • Craters are named after historical names that were connected to the goddess Vesta, and famous Roman women after.
  • Regions are named after the discoverer of Vesta and by scientists who were involved in the exploration of Vesta.
  • Other structures are named after places that are associated with vestal virgins.

On 30 September 2011 the IAU recognized for the first time to the naming of 14 craters and a Tholus. The structures designated in diameter between 0.7 ( Claudia ) and 500 km ( Rheasilvia ).

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