Sunday, May 27, 2018

Vesta, second most massive astreroid



-  2094  -  Vesta is the second most massive body in the asteroid belt, surpassed only by Ceres, which is classified as a dwarf planet. The brightest asteroid in the sky, Vesta is occasionally visible from Earth with the naked eye. It is the first asteroid to be visited by a spacecraft. The Dawn mission orbited Vesta in 2011, providing new insights into this rocky world.
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-----------------------------  2094  -  Vesta, second most massive asteroid
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-  Vesta is the second most massive body in the asteroid belt, surpassed only by Ceres, which is classified as a dwarf planet. The brightest asteroid in the sky, Vesta is occasionally visible from Earth with the naked eye. It is the first asteroid to be visited by a spacecraft. The Dawn mission orbited Vesta in 2011, providing new insights into this rocky world.
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-  In 1596, while determining the elliptical shape of planetary orbits, Johannes Kepler came to believe that a planet should exist in the gap between Mars and Jupiter. Mathematical calculations made in 1772 seemed to support this prediction.
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-   In August 1798, a German astronomer Heinrich Olbers discovered the second known asteroid, Pallas. In a letter to a fellow astronomer, he put forth the first theory of asteroid origin. He wrote, "Could it be that Ceres and Pallas are just a pair of fragments of a once greater planet which at one time occupied its proper place between Mars and Jupiter?"
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-  Olbers reasoned that the fragments of such a planet would intersect at the point of the explosion, and again in the orbit directly opposite. He observed these two areas nightly, and on March 29, 1807 he discovered Vesta.  After measuring several nights' worth of observations, Olbers sent his calculations to mathematician Carl Friedrich Gauss, who remarkably computed the orbit of Pallas in only 10 hours. As such, he was given the honor of naming the new body. He chose the name Vesta, goddess of the hearth, and sister to Ceres.
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-   Vesta is unique among asteroids in that it has light and dark patches on the surface, much like the moon. Ground-based observations determined that the asteroid has basaltic regions, meaning that lava once flowed across its surface. It has an irregular shape, roughly that of an oblate spheroid,  a  smooshed sphere. 
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-------------------------------------  Diameter:  ----------   329 miles (530 kilometers)
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------------------------------------- Mass: :  -------------    5.886 X 1020 lbs. (2.67 x 1020 kilograms)
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------------------------------------- Temperature: :  -----   85 to 255 K (minus 306 to 0 Fahrenheit).
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------------------------------------- Albedo:  ------------    0.4322
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------------------------------------- Rotation period:------ 5.342 hours
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------------------------------------- Orbital period:  ------   3.63 years
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------------------------------------- Eccentricity: :  ------   .0886
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------------------------------------- Aphelion: :  ---------    2.57 AU
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-  ------------------------------------Perihelion:------------- 2.15 AU
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------------------------------------  Closest to Earth: ------  1.14 AU
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-   When Vesta made this close approach to Earth in 1996, the Hubble Space Telescope mapped its topographic surface and features. This revealed a large crater at the south pole that slices into its interior. The crater averages 460 km in diameter.
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-  Vesta itself is only 530 km across. It cuts an average of 13 km into the crust, and most likely formed from an impact in the asteroid's early life. The material ejected from this collision resulted in a number of smaller asteroids that orbit near their parent, as well as some of the meteorites that have crashed into Earth.
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-  Unlike most asteroids, the interior of Vesta is differentiated.  Like the terrestrial planets, the asteroid has a crust of cooled lava covering a rocky mantle and an iron and nickel core. This lends credence to the argument for naming Vesta as a protoplanet, rather than as an asteroid.
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-  Vesta's core accreted rapidly within the first 10 million years after the formation of the solar system. The basaltic crust of Vesta also formed quickly, over the course of a few million years. Volcanic eruptions on the surface stemmed from the mantle, lasting anywhere from 8 to 60 hours. The lava flows themselves ranged from a few hundred meters to several kilometers, with a thickness between 5 to 20 meters. The lava cooled rapidly, only to be buried again by more lava until the crust was complete.
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-   Dawn's gravity put its core at about 18 percent of Vesta's mass, or proportionally about two-thirds as massive as Earth's core.  If it weren't for Jupiter, Vesta could have had a good chance at becoming a planet.
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-  In 1960, a fireball streaking through the sky over Millbillillie, Australia, announced the arrival of a piece of Vesta on Earth. Composed almost entirely of pyroxene, a mineral found in lava flows, the meteorite bears the same spectrometry analysis as Vesta.
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-  NASA's Dawn spacecraft visited the asteroid in 2012 and discovered that the rocky body had a surprising amount of hydrogen on its surface. It also found bright, reflective regions that may have been left over from its birth.
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- There is a massive mountain that towers over Vesta's southern pole. The enormous mountain reaches up over 65,000 feet in height, making it nearly as tall as Olympus Mons, the largest mountain ,and volcano, in the solar system. Olympus Mons soars about 15 miles above the surface of Mars.
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-  The south polar mountain is larger than the big island of Hawaii, the largest mountain on Earth, as measured from the ocean floor.  Liquid water once flowed across the asteroid. Images captured by the Dawn spacecraft revealed curved gullies and fan-shaped deposits within eight different Vesta impact craters. All eight of the craters are thought to have formed within the last few hundred million years, fairly recent in the lifetime of the 4.5-billion-year-old asteroid.
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-  Nobody expected to find evidence of water on Vesta. The surface is very cold and there is no atmosphere, so any water on the surface evaporates. The features could have been created by debris flows, as opposed to pure water rivers or streams, that sculpted the Vesta gullies.  Meteorites bombarding the asteroid melted ice deposits beneath the surface, sending liquid water and small rocky particles flowing down the crater walls. Such activity suggests the presence of ice buried beneath the surface.
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-  The craters with curved gullies are associated with pitted terrain, which has been independently suggested as evidence for loss of volatile gases from Vesta.  Ice could have been responsible for modifying Vesta's surface. In 2017, a study suggested that smooth patches of terrain on the asteroid frequently possessed high concentrations of hydrogen, which is often seen when solar radiation breaks down water molecules.
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-  Modifications of the surface by melting of buried ice could be responsible for smoothing those areas.   Buried ice could have been brought to the surface after an impact, which caused heated ice to melt and travel up through the fractures to the surface.
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-  Dawn also observed signs of hydrated minerals containing water molecules on Vesta's surface, which could also hint of the presence of buried ice. The hydrated materials were associated with older terrains, and could have been delivered by impacts of material from farther out in the solar system.
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-   A low-altitude map of Vesta revealed a rich geology. The steep slopes found on the asteroid, combined with its high gravity, paves the way for rocks to roll downward, exposing other material. Dawn revealed a variety of minerals, including some bright and dark materials that could relate to potential buried ice.

-   Vesta's unique composition means that it is responsible for an entire group of meteorites. The HED meteorites, made up of howardites, eucrites and diogenites,  tell the story of Vesta's early life. Eucrites form from hardened lava, while diogenites come from beneath the surface. Howardites are a combination of the two, formed when a large impact mixed the two sections together. 
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-  Vesta has been suspected as being the source of the HED meteorites since 1970. Dawn's mapping spectrometer verified that proposition. The Dawn team thinks the HEDs came from an impact basin named Rheasilvia, after an ancient Roman vestal virgin priestess. At 310 miles in diameter, Rheasilvia is nearly as large as Vesta itself. It most likely formed from a collision that stripped away most of the southern hemisphere's crust, revealing the asteroid's interior.
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-  Vesta likely came close to shattering,  the blow left concentric sets of troughs, fracture lines around Vesta's equator. Parallel troughs may be another sign of the enormous impact.
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-  In September 2007, NASA launched the Dawn mission, which is unique in that it was the first craft to enter orbit around one solar system body, then proceed to a second. Dawn entered orbit around Vesta in July 2011. After studying the asteroid for a year, it left Vesta encountered Ceres in March 2015
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-  NASA's Dawn mission is to study the characteristics of the early solar system by analyzing the two asteroids, which are very different. Ceres is wet, with seasonal polar caps, and may have a thin atmosphere. Vesta, on the other hand, is dry and rocky. Studying the unique spectral signatures in its rocky crust will expand our knowledge of our own planet, as well as Mars and Mercury.
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-  Given their size, the two are actually regarded as protoplanets, or small planets. The gravitational pull of Jupiter disrupted their formation. Without the presence of the gas giant, the two may well have continued to evolve into full-size planets.
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-  We now know that Vesta is the only intact, layered planetary building block surviving from the very earliest days of the solar system.  Dawn's study of Vesta allowed for the creation of the best map to date of the asteroid.  In October 2010, the Hubble Space Telescope imaged Vesta again. The resulting data revealed that the asteroid was tilted approximately four degrees more than scientists originally thought. These findings helped NASA to place the spacecraft in the appropriate polar orbit around the asteroid. Dawn requires light from the sun in order to perform its mapping and imaging assignments.
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-  See Review 1618 to learn more about Vesta  It includes information of how a gravity map was used to map the concentrations of mass on the asteroid. 
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-  See Review 847 about Ceres the 5th planet in our solar system, now a protoplanet. 
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 -------------------------   Sunday, May 27, 2018   --------------------------------
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