Rheasilvia/ˌriːəˈsɪlviə/is the largestimpact crateron the asteroidVesta.It is 505 km (314 mi) in diameter, which is 90% the diameter of Vesta itself, and is 95% themean diameterof Vesta, 529 km (329 mi). However, the mean is affected by the crater itself. It is 89% the mean equatorial diameter of 569 km (354 mi), making it one of thelargest craters in the Solar System,and at 75°S latitude, covers most of the southern hemisphere. The peak in the center of the crater is 200 km (120 mi) in diameter, and rises 22.5 km (14.0 mi; 74,000 ft) from its base,[3][2]making it one of thetallest mountains known in the Solar System.
 Southern hemisphere of Vesta as imaged byDawn,showing Rheasilvia crater | |
| Location | South polar region,Vesta |
|---|---|
| Coordinates | 71°57′S86°18′E/ 71.950°S 86.300°E[1] |
| Diameter | 505 km (314 mi) |
| Peak | 20–25 km (12–16 mi)(central peak)[2][3] |
| Discoverer | Hubble Space Telescope |
| Eponym | Rhea Silvia,a mythologicalvestal virginand mother of the founders of Rome, Romulus and Remus |
Observation and naming
editRheasilvia was discovered inHubble Space Telescopeimages in 1997,[4]but was not named until the arrival of theDawnspacecraftin 2011. It is named afterRhea Silvia,a mythologicalvestal virginand mother of the founders of Rome, Romulus and Remus. The nameRheasilviawas officially approved by theInternational Astronomical Union(IAU) on 30 September 2011.[1]
Characteristics
editThe crater partially obscures an earlier crater, namedVeneneia,that at 395 km (245 mi) is almost as large.[5]
Rheasilvia has anescarpmentalong part of its perimeter which rises 4–12 km (2.5–7.5 mi) above the surrounding terrain. The crater floor lies about 13 kilometres (8.1 mi) below the surrounding surface. This basin consists of undulating terrain and a central mound almost 200 km (120 mi) in diameter, which rises 20–25 km (12–16 mi; 66,000–82,000 ft) from its base,[3][2]one of thetallest known mountains in the Solar System,and possibly formed due to a planetary scale impact.[6]
Spectroscopicanalyses ofHubbleimages have shown that this crater has penetrated deep through several distinct layers of the crust, and possibly into themantle,as indicated by spectral signatures ofolivine.[7]
Vesta has a series of troughs in an equatorial region concentric to Rheasilvia. These are thought to be large-scale fractures resulting from the impact. The largest isDivalia Fossae,approx. 22 km (14 mi) wide and 465 km (289 mi) long.
It is estimated that the impact responsible excavated about 1% of the volume of Vesta, and it is likely that theVesta familyandV-type asteroidsare the products of this collision. If this is the case, then the fact that 10-km fragments have survived bombardment until the present indicates that the crater is at most about 1 billion years old.[8]It would also be the origin of theHED meteorites.Known V-type asteroids account for 6% of the ejected volume, with the rest of the fragments presumably either too small to observe, or removed from theasteroid beltby approaching the 3:1Kirkwood gap,by theYarkovsky effect,or (in the case of small fragments) byradiation pressure.
Gallery
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See also
editReferences
edit- ^ab"Rheasilvia".Gazetteer of Planetary Nomenclature.USGS Astrogeology Research Program.(NASA coordinates)
- ^abcVega, Priscilla (11 October 2011)."New View of Vesta Mountain From NASA's Dawn Mission".dawn.jpl.nasa.gov.NASA.Archived fromthe originalon 17 October 2013.Retrieved17 February2018.
- ^abcSchenk, Paul; et al. (11 May 2012). "The Geologically Recent Giant Impact Basins at Vesta's South Pole".Science.336(6082):694–697.Bibcode:2012Sci...336..694S.doi:10.1126/science.1223272.PMID22582256.S2CID206541950.
- ^"Hubble Reveals Huge Crater on the Surface of the Asteroid Vesta".HubbleSite.Space Telescope Science Institute.4 September 1997.Retrieved4 July2018.
- ^Drake, Nadia(22 March 2012)."Vesta seems more planet than asteroid".Science News.
- ^Karimi, Saman; Dombard, Andrew J. (2016)."On the possibility of viscoelastic deformation of the large south polar craters and true polar wander on the asteroid Vesta".Journal of Geophysical Research.121(9):1786–1797.Bibcode:2016JGRE..121.1786K.doi:10.1002/2016JE005064.
- ^Thomas, Peter C.; et al. (July 1997)."Vesta: Spin Pole, Size, and Shape from HST Images".Icarus.128(1):88–94.Bibcode:1997Icar..128...88T.doi:10.1006/icar.1997.5736.
- ^Binzel, Richard P.; et al. (1997)."Geologic Mapping of Vesta from 1994 Hubble Space Telescope Images".Icarus.128(1):95–103.Bibcode:1997Icar..128...95B.doi:10.1006/icar.1997.5734.
