Feralia Planitia () is the third-largest known

impact structure An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surface e ...

on the asteroid Vesta, after

Rheasilvia Rheasilvia is the largest impact crater 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 equ ...

and

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

. It is one of several old, degraded impact basins that predate the Rheasilvia basin that now dominates Vesta. It is situated near the equator, and is across east to west, though compressed latitudinally by the Rheasilvia impact.

Observation and naming

Feralia Planitia was first seen in distant observations of Vesta by the

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 ...

(HST), which observed Vesta in 1994, 1996, 2007, and 2010. Feralia Planitia was then given the informal provisional designation of Feature Y. Feralia Planitia, alongside Vesta's other surface features, were resolved in detail for the first time by the ''

Dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the diffuse sky radiation, appearance of indirect sunlight being Rayleigh scattering, scattered in Earth's atmosphere, when the centre of the Sun's disc ha ...

'' orbiter, which orbited Vesta from 16 July 2011 to 4 September 2012. The feature was then named after the ancient

Roman Roman or Romans most often refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of Roman civilization *Epistle to the Romans, shortened to Romans, a letter w ...

public festival of

Feralia Ferālia was an ancient Roman public festival Dumézil, Georges. ''Archaic Roman Religion''. p. 366. celebrating the Manes (Roman spirits of the dead, particularly the souls of deceased individuals) which fell on 21 February as recorded by ...

, where citizens would place offerings at the tombs of the dead. The name Feralia Planitia 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 27 December 2011.

Geology and characteristics

Feralia Planitia, located near the equator, dominates Vesta's eastern hemisphere. The basin is roughly ellipsoidal and elongated east to west and very roughly spans 130 by 300 kilometers. Feralia Planitia is surrounded by elevated terrain, with the northern rim dropping roughly 5–7 kilometers and the southern rim dropping by up to 14 kilometers. It borders the cratered highlands of

Vestalia Terra } Vestalia Terra () is a large highland plateau on the giant asteroid Vesta. Situated in Vesta's eastern hemisphere, Vestalia Terra is located near the equator and hosts the tallest point on Vesta. One of the largest named features on Vesta, it c ...

to the west, the rim of

to the south,

Divalia Fossae Divalia Fossae is the large series of parallel equatorial troughs on the giant asteroid 4 Vesta. It is one of the longest chasms in the Solar System, stretching across roughly two-thirds of Vesta's equator. The trough system is named after the ...

to the east, and

Saturnalia Fossae Saturnalia Fossae is a series of parallel Veneneian troughs in the northern hemisphere of the giant asteroid 4 Vesta. It is thought to be a shock fractures resulting from the impact that created Veneneia crater, which it is concentric with. It ...

to the northwest. Two major impact craters further alter Feralia Planitia's rim: the ~45 km Lepida on the northern wall, and the ~35–40 km Oppia on the southern wall. Feralia Planitia is likely an ancient, degraded impact basin, though whether it was formed by a single

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effe ...

or multiple remains unclear. The surrounding cratered highlands likely represent ejecta blasted out by the impact event(s) that created Feralia Planitia. Meanwhile, he interior of Feralia Planitia is comparatively unmodified by the extensive troughs of Divalia Fossae and Saturnalia Fossae, though some of their troughs extend into the walls of Feralia Planitia, indicating that they are younger than the basin. As Divalia Fossae and Saturnalia Fossae are similar in age to the Rheasilvia and

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

impact basins, this indicates that both the trough systems and the two major southern impact basins are younger than Feralia Planitia. However, a precise date for Feralia Planitia's formation cannot be determined through

crater counting Crater counting is a method for estimating the age of a planet's surface based upon the assumptions that when a piece of planetary surface is new, then it has no impact craters; impact craters accumulate after that at a rate that is assumed known. ...

, as the basin underwent a resurfacing event roughly 3.62 billion years ago. Feralia Planitia's surface is partially composed of

eucrite Eucrites are achondritic stony meteorites, many of which originate from the surface of the asteroid 4 Vesta and are part of the HED meteorite clan. They are the most common achondrite group with over 100 meteorites found. Eucrites consist of b ...

s, a type of

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic rock containing

anorthite Anorthite (< ''an'' 'not' + ''ortho'' 'straight') is the

calcium

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

, and

augite Augite, also known as Augurite, is a common rock-forming pyroxene mineral with formula . The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees. Characteristics Augite is a solid soluti ...

. This is in contrast to the older northern and northeastern highlands, whose mineralogy is dominated by

howardite Howardites are achondritic stony meteorites that originate from the surface of the asteroid 4 Vesta, and as such are part of the HED meteorite clan. There are about 200 distinct members known. Characteristics They are a regolith breccia consist ...

, a mixture of eucrite and

diogenite Diogenites are a group of the HED meteorite clan, a type of achondritic stony meteorites. Origin and composition Diogenites are currently believed to originate from deep within the crust of the asteroid 4 Vesta, and as such are part of the HED ...

. Feralia Planitia is the site of a negative

gravity anomaly The gravity anomaly at a location on the Earth's surface is the difference between the observed value of gravity and the value predicted by a theoretical model. If the Earth were an ideal oblate spheroid of uniform density, then the gravity meas ...

References

{{4 Vesta Impact craters on asteroids Surface features of 4 Vesta Extraterrestrial plains