Rheasilvia is the largest

impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...

on the asteroid Vesta. It is in diameter, which is 90% the diameter of Vesta itself, and is 95% the mean diameter of Vesta, . However, the mean is affected by the crater itself. It is 89% the mean equatorial diameter of , making it one of the

largest craters in the Solar System Following are the largest impact craters on various worlds of the Solar System. For a full list of named craters, ''see List of craters in the Solar System''. The ratio column compares the crater diameter with the diameter of the impacted celesti ...

, and at 75°S latitude, covers most of the southern hemisphere. The peak in the center of the crater is in diameter, and rises from its base, making it one of the tallest mountains known in the Solar System.

Observation and naming

Rheasilvia was discovered in

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

images in 1997, but was not named until the arrival of the ''Dawn'' spacecraft in 2011. It is named after

Rhea Silvia Rhea (or Rea) Silvia (), also known as Ilia, (as well as other names) was the mythical mother of the twins Romulus and Remus, who founded the city of Rome.Livy I.4.2 This event was portrayed numerous times in Roman art. Her story is told in the ...

, a mythological

vestal virgin In ancient Rome, the Vestal Virgins or Vestals (, singular ) were priestesses of Vesta, virgin goddess of Rome's sacred hearth and its flame. The Vestals were unlike any other public priesthood. They were chosen before puberty from several s ...

and mother of the founders of Rome,

Romulus and Remus In Roman mythology, Romulus and (, ) are twins in mythology, twin brothers whose story tells of the events that led to the Founding of Rome, founding of the History of Rome, city of Rome and the Roman Kingdom by Romulus, following his frat ...

. The name ''Rheasilvia'' was officially approved by the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

(IAU) on 30 September 2011.(NASA coordinates)

Characteristics

The crater partially obscures an earlier crater, named

Veneneia Veneneia is the second-largest impact crater on asteroid 4 Vesta, at 52°S latitude.

, that at is almost as large. Rheasilvia has an

escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. Due to the similarity, the term '' scarp'' may mistakenly be incorrectly used inte ...

along part of its perimeter which rises above the surrounding terrain. The crater floor lies about below the surrounding surface. This basin consists of undulating terrain and a central mound almost in diameter, which rises from its base, one of the tallest known mountains in the Solar System, and possibly formed due to a planetary scale impact. Spectroscopic analyses of ''Hubble'' images have shown that this crater has penetrated deep through several distinct layers of the crust, and possibly into the mantle, as indicated by spectral signatures of

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

. 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 is Divalia Fossae, approx. wide and long. It is estimated that the impact responsible excavated about 1% of the volume of Vesta, and it is likely that the Vesta family and V-type asteroids are 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. It would also be the origin of the HED 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 the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

by approaching the 3:1

Kirkwood gap A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter. The gaps were first n ...

, by the Yarkovsky effect, or (in the case of small fragments) by

radiation pressure Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...

Gallery

References

{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Surface features of main-belt asteroids Impact craters on asteroids Surface features of 4 Vesta Tallest things

Observation and naming

Characteristics

Gallery

See also

References