Rheasilvia is the most prominent surface feature on the

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

Vesta and is thought to be an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

. 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, 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.

Discovery

Rheasilvia was discovered in

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

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. Her story is told in the first book of ''Ab Urbe Condita Libri'' of Livy and in Cassius D ...

, a mythological

vestal virgin In ancient Rome, the Vestal Virgins or Vestals ( la, Vestālēs, 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 ...

and mother of the founders of Rome, Romulus and Remus.(NASA coordinates)

Characteristics

The crater partially obscures an earlier crater, named

Veneneia Veneneia is the second-largest crater on asteroid 4 Vesta, at 52°S latitude. 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. The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''esca ...

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 Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...

analyses of ''Hubble'' images have shown that this crater has penetrated deep through several distinct layers of the crust, and possibly into the

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

, as indicated by spectral signatures of

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

. 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 Fossa, 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 The Vesta family (adj. ''Vestian''; ) is a family of asteroids. The cratering family is located in the inner asteroid belt in the vicinity of its namesake and principal body, 4 Vesta. It is one of the largest asteroid families with more than ...

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 meteorite HED meteorites are a clan (subgroup) of achondrite meteorites. HED stands for "howardite– eucrite– diogenite". These achondrites came from a differentiated parent body and experienced extensive igneous processing not much different from the ma ...

s. 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 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. For example, there ...

, by the

Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km i ...

, or (in the case of small fragments) by

radiation pressure Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is a ...

Gallery

References

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

Discovery

Characteristics

Gallery

See also

References