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Gusev is a crater on the planet Mars and is located at . The crater is about 166 kilometers in diameter and formed approximately three to four billion years ago. It was named after Russian astronomer Matvei Gusev (1826–1866) in 1976. A channel system named Ma'adim Vallis drains into it that probably carried liquid water, or water and ice, at some point in Mars' past. The crater appears to be an old crater lake bed, filled with sediments up to 3000 feet thick. Some exposed outcrops appear to show faint layering, and some researchers also believe that landforms visible in images of the mouth of Ma'adim Vallis where it enters Gusev resemble landforms seen in some terrestrial river deltas. Deltas of this nature can take tens or hundreds of thousands of years to form on Earth, suggesting that the water flows may have lasted for long periods. Orbital images indicate that there may once have been a very large lake near the source of Ma'adim Vallis that could have provided the source of this water. It is not known whether this flow was slow and continuous, punctuated by sporadic large outbursts, or some combination of these patterns. More recently, satellite images showed the trails of dust devils on Gusev's floor. The Spirit rover later photographed dust devils from the ground, and likely owes much of its longevity to dust devils cleaning its solar panels. On January 3, 2004, Gusev was the landing site of the first of NASA's two Mars Exploration Rovers, named Spirit. It is hoped that the numerous smaller and more recent craters in this region will have exposed sedimentary material from early eras, although at first the region proved disappointing in its lack of available bedrock for study on the flat lava plains of the crater, Spirit's landing site. It eventually arrived at the Columbia Hills, however, and rocks examined in that region show that the Columbia Hills did have small amounts of briny (salty) water interacting with them in ancient times, though nowhere near as much as Meridiani Planum, the landing area for Spirit's twin, Opportunity. However, in 2009, ''Spirit'' became stuck in the soil of the region, and in 2010 went offline after a harsh Martian winter. It is also considered a potential landing site for the ''Mars 2020'' rover. ==Spirit Rover's rocks and minerals discoveries on Mars== The rocks on the plains of Gusev are a type of basalt. They contain the minerals olivine, pyroxene, plagioclase, and magnetite, and they look like volcanic basalt as they are fine-grained with irregular holes (geologists would say they have vesicles and vugs). Much of the soil on the plains came from the breakdown of the local rocks. Fairly high levels of nickel were found in some soils; probably from meteorites. Analysis shows that the rocks have been slightly altered by tiny amounts of water. Outside coatings and cracks inside the rocks suggest water deposited minerals, maybe bromine compounds. All the rocks contain a fine coating of dust and one or more harder rinds of material. One type can be brushed off, while another needed to be ground off by the Rock Abrasion Tool (RAT). There are a variety of rocks in the Columbia Hills (Mars), some of which have been altered by water, but not by very much water. The dust in Gusev Crater is the same as dust all around the planet. All the dust was found to be magnetic. Moreover, Spirit found the magnetism was caused by the mineral magnetite, especially magnetite that contained the element titanium. One magnet was able to completely divert all dust hence all Martian dust is thought to be magnetic. The spectra of the dust was similar to spectra of bright, low thermal inertia regions like Tharsis and Arabia that have been detected by orbiting satellites. A thin layer of dust, maybe less than one millimeter thick covers all surfaces. Something in it contains a small amount of chemically bound water. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gusev (Martian crater)」の詳細全文を読む スポンサード リンク
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