| 词条 | Lyot (Martian crater) | |||
| 释义 |
| titlecolor = #FA8072 | title = Lyot Crater | image = Lyot Mars Crater Dunes.JPG | caption = Lyot Crater Dunes, as seen by HiRISE. Click on image to see light toned deposits and dust devil tracks. | region = Ismenius Lacus quadrangle | coordinate_title = Coordinates | globe = Mars | coordinates = {{coord|50.8|N|330.7|W|globe:mars_type:landmark|display=inline,title}} | diameter = 236 km | eponym = Bernard Lyot, French astronomer (1897–1952) }}Lyot is a large crater in the Vastitas Borealis region of Mars, located at 50.8° north latitude and 330.7° west longitude within the Ismenius Lacus quadrangle. It is 236 km in diameter. Its name refers to Bernard Lyot, a French astronomer (1897–1952).[1] Lyot stands out on the flat plains of Vastitas Borealis, which is generally flat and smooth with few large craters.[2] Lyot is the deepest point in Mars's northern hemisphere.[3] South are the Protonilus Mensae and further southeast are Protonilus Mensae. Also west is the smaller Micoud and east-southeast is Moreux. Lyot also features a central peak in the middle. Research published in 2009 describes evidence for liquid water in Lyot in the past.[4] Many channels have been found near Lyot Crater. Research, published in 2017, concluded that the channels were made from water released when the hot ejecta landed on a layer of ice that was 20 to 300 meters thick. Calculations suggest that the ejecta would have had a temperature of at least 250 degrees Fahrenheit. The valleys seem to start from beneath the ejecta near the outer edge of the ejecta. One evidence for this idea is that there are few secondary craters nearby. Few secondary craters were formed because most landed on ice and did not affect the ground below. The ice accumulated in the area when the climate was different. The tilt or obliquity of the axis changes frequently. During periods of greater tilt, ice from the poles is redistributed to the mid-latitudes. The existence of these channels is unusual because although Mars used to have water in rivers, lakes, and an ocean, these features have been dated to the Noachian and Hesperian periods—4 to 3 billion years ago.[5][6][7] Former riversImages from Mars Reconnaissance Orbiter show valleys carved by rivers on the floor of Lyot Crater. Scientists are excited because the rivers seem to have formed more recently than others on Mars; water could have flowed in them only 1.25 million years ago. The source of the water is believed to have been ice from nearby glaciers. The river valleys are over 250 meters wide and tens of kilometers long.[8] Dust devil tracksMany areas on Mars, including Lyot, experience the passage of giant dust devils. A thin coating of fine bright dust covers most of the Martian surface. When a dust devil goes by it blows away the coating and exposes the underlying dark surface. These dust devils have been seen from the ground and high overhead from orbit. GalleryInteractive Mars map{{Mars map}}See also
References1. ^{{gpn|3538|Lyot}} 2. ^U.S. department of the Interior U.S. Geological Survey, Topographic Map of the Eastern Region of Mars M 15M 0/270 2AT, 1991 3. ^http://space.com/scienceastronomy/090514--mars-rivers.html 4. ^{{cite journal |last1=Dickson |first1=J. L. |last2=Fassett |first2=C. I. |last3=Head |first3=J. W. |title=Amazonian‐aged fluvial valley systems in a climatic microenvironment on Mars: Melting of ice deposits on the interior of Lyot Crater |journal=Geophysical Research Letters |date=2009 |volume=36 |issue=8 |doi=10.1029/2009GL037472|bibcode=2009GeoRL..3608201D}} 5. ^{{cite journal|doi=10.1002/2017GL073821 | volume=44 | title=Extensive Amazonian-aged fluvial channels on Mars: Evaluating the role of Lyot crater in their formation | journal=Geophysical Research Letters | pages=5336–5344 | last1 = Weiss | first1 = David K.| bibcode=2017GeoRL..44.5336W }} 6. ^{{cite journal | last1 = Weiss | first1 = D. | display-authors = etal | year = 2017 | title = Extensive Amazonian-aged fluvial channels on Mars: Evaluating the role of Lyot crater in their formation | url = | journal = Geophysical Research Letters | volume = 44| issue = | pages = 5336–5344| doi = 10.1002/2017GL073821 | bibcode = 2017GeoRL..44.5336W}} 7. ^http://spaceref.com/mars/hot-rocks-led-to-relatively-recent-water-carved-valleys-on-mars.html 8. ^http://www.space.com/scienceastronomy/090514-mars-rivers.html External links{{commons category|Lyot (Martian crater)}}{{Geography of Mars}}{{portal bar|Mars}} 2 : Impact craters on Mars|Ismenius Lacus quadrangle |
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