E-type (enstatite achondrite–type) asteroids are

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s thought to have

enstatite Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and m ...

(MgSiO₃)

achondrite An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystalli ...

surfaces. They form a large proportion of asteroids inward of 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 ...

known as

Hungaria asteroids The Hungaria asteroids, also known as the Hungaria group, are a dynamical group of asteroids in the asteroid belt which orbit the Sun with a semi-major axis (longest radius of an ellipse) between 1.78 and 2.00 astronomical units (AU). They are the ...

, but rapidly become very rare as the asteroid belt proper is entered. Some are quite far from the inner edge of the asteroid belt, such as

64 Angelina 64 Angelina is an asteroid from the central region of the asteroid belt, approximately 50 kilometers in diameter. It is an unusually bright form of E-type asteroid. Discovery and naming Angelina was discovered on March 4, 1861, by a prolific ...

. They are thought to have originated from the highly reduced mantle of a differentiated asteroid.

Description

E-type asteroids have a high

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

(0.3 or higher), which distinguishes them from the more common M-type

s. Their

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

is featureless flat to reddish. Probably because they originated from the edge of a larger parent body rather than a core, E-types are all small, with only three (

44 Nysa 44 Nysa is a large and very bright main-belt asteroid, and the brightest member of the Nysian asteroid family. It is classified as a rare class E asteroid and is probably the largest of this type (though 55 Pandora is only slightly smaller). ...

55 Pandora 55 Pandora is a fairly large and very bright asteroid in the asteroid belt. Pandora was discovered by American astronomer and Catholic priest George Mary Searle on September 10, 1858, from the Dudley Observatory near Albany, NY. It was his f ...

) having diameters above 50 kilometres and no others above 25 kilometers (the biggest three also orbit atypically far, c. 3 AU, from the Sun).

Aubrite Aubrites are a group of meteorites named for Aubres, a small achondrite meteorite that fell in 1836 in Aubres near Nyons, France. They are primarily composed of the orthopyroxene enstatite and are often called enstatite achondrites. Their igneou ...

s (enstatite achondrite meteorites) are believed to come from E-type asteroids, because Aubrites could be linked to the E-type asteroid

3103 Eger 3103 Eger is an Apollo and Mars-crosser asteroid that was discovered in 1982, by Miklós Lovas. It was named after the city of Eger, Hungary. It has an albedo of 0.64, making it a highly reflective asteroid. Description It has made and wil ...

. This grouping may be related to the Xe-type of the

SMASS classification An asteroid spectral type is assigned to asteroids based on their reflectance spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally different ...

E-Belt

The E-type asteroids of the Hungaria family are thought to be the remains of the hypothetical E-belt asteroid population.Late, Late Heavy Bombardment - Bill Bottke
(SETI Talks) – Youtube.com The dispersal of most of that hypothetical E-Belt might have been caused by the outward migration of the

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...

s of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

according to simulations done under the

Nice model In astronomy, the Nice () model is a scenario for the dynamical evolution of the Solar System. It is named for the location of the Côte d'Azur Observatory—where it was initially developed in 2005—in Nice, France. It proposes the migration ...

– and these dispersed E-Belt asteroids might in turn have been the impactors of the

Late Heavy Bombardment The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized astronomical event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According ...

Exploration

On September 5, 2008, ESA's robotic spaceprobe

Rosetta Rosetta ( ) or Rashid (, ; ) is a port city of the Nile Delta, east of Alexandria, in Egypt's Beheira governorate. The Rosetta Stone was discovered there in 1799. Founded around the 9th century on the site of the ancient town of Bolbitine, R ...

visited the E-type asteroid

2867 Šteins 2867 Šteins (provisional designation ) is an irregular, diamond-shaped background asteroid from the inner regions of the asteroid belt, approximately in diameter. It was discovered on 4 November 1969 by Soviet astronomer Nikolai Chernykh at t ...

.H. U. Keller, et al. - E-Type Asteroid (2867) Steins as Imaged by OSIRIS on Board Rosetta - Science 8 January 2010: Vol. 327. no. 5962, pp. 190 - 193
Spectral data from the spacecraft confirmed the asteroid was composed mainly of iron-poor minerals such as

(magnesium-rich pyroxene),

forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich Endmember, end-member of the olivine solid solution series. It is Isomorphism (crystallography), isomorphous with the iron-rich end-member, fayalit ...

(magnesium-rich olivine) and

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

References

{{More citations needed, date=September 2008 Asteroid spectral classes *

Description

E-Belt

Exploration

See also

References