V-type asteroid

V-type asteroids, also known as Vestoids, are a class of asteroids whose spectral type is characterized by a strong absorption feature at wavelengths longward of 0.75 μm, similar to that of 4 Vesta, the second-most-massive asteroid in the asteroid belt.^[1] These asteroids comprise approximately 6% of main-belt asteroids and are characterized by their basaltic surface composition, making them distinct from other asteroid types.^[2]

Characteristics

Physical Properties

V-type asteroids are relatively bright objects with moderate to high albedo values typically ranging from 0.20 to 0.40.^[3] They are distinguished from other asteroid types by their basaltic composition, which indicates that they originated from differentiated parent bodies that underwent volcanic or igneous processing.^[4]

The mean diameter of V-type asteroids varies considerably, from sub-kilometer objects to 4 Vesta itself with a mean diameter of approximately 525 kilometers.^[5] Most V-types outside the Vesta family are relatively small, with diameters typically less than 10 kilometers.

Spectral Features

The electromagnetic spectrum of V-type asteroids exhibits several diagnostic features:^[6]

• A very strong absorption feature longward of 0.75 μm attributed to Fe²⁺ in pyroxene
• A second absorption feature centered near 0.9-1.0 μm, also due to pyroxene
• Very steep red spectral slope shortward of 0.7 μm
• A weak absorption feature at 0.506 μm due to Fe²⁺ spin-forbidden transitions in pyroxene

The Band I center position typically ranges from 0.90 to 0.94 μm, while the Band II center is usually located between 1.89 and 2.00 μm.^[7] The ratio of Band II to Band I depths (BII/BI) typically ranges from 1.5 to 2.5 for V-type asteroids.

Composition

V-type asteroids are composed primarily of basaltic material containing pyroxene and plagioclase feldspar.^[8] The pyroxene composition is typically low-calcium pyroxene (orthopyroxene) with varying amounts of high-calcium pyroxene (clinopyroxene). The visible and near-infrared spectra of V-type asteroids closely resemble those of basaltic achondrite meteorites, particularly the HED meteorites (Howardites, Eucrites, and Diogenites).^[9]

Spectroscopic analysis has revealed compositional variations among V-types:^[10]

• Eucrite-like: High calcium content, consistent with basaltic eucrite meteorites
• Diogenite-like: Low calcium content, consistent with orthopyroxenitic diogenite meteorites
• Howardite-like: Intermediate composition, mixture of eucrite and diogenite material

Distribution

Vesta Family Members

The vast majority of V-type asteroids are members of the Vesta family along with Vesta itself.^[11] The Vesta family is one of the largest asteroid families with more than 15,000 known members.^[12] Spectroscopic studies indicate that approximately 85% of the members of the Vesta dynamical family are V-type asteroids.^[13]

Mars-Crossing V-types

Several V-type asteroids have been identified as Mars-crossers, including:^{[14][failed verification]}

• 9969 Braille

Recent systematic searches have confirmed three additional V-type asteroids in the Mars crossing region through spectroscopic observations.^[15]

Near-Earth V-types

Several V-type asteroids have been identified among Near-Earth objects:^[16]

• 3908 Nyx
• 4055 Magellan
• (137052) Tjelvar

Non-Vesta Family V-types

There is a scattered group of V-type asteroids in the general vicinity of the Vesta family but not dynamically associated with it.^[17] As of current surveys, 22 V-type asteroids have been identified outside the Vesta family in the inner asteroid belt:^[18]

• 809 Lundia — Orbits within the Flora family region
• 956 Elisa — Located near 2.4 AU
• 1459 Magnya — Orbits in the outer asteroid belt at 3.14 AU, too far from Vesta to be genetically related; may be the remains of a different ancient differentiated body^[19]
• 2113 Ehrdni
• 2442 Corbett
• 2566 Kirghizia
• 2579 Spartacus — Contains a significant portion of olivine, which may indicate origin deeper within a differentiated body than other V-types^[20]
• 2640 Hallstrom
• 2653 Principia
• 2704 Julian Loewe
• 2763 Jeans
• 2795 Lepage
• 2851 Harbin
• 2912 Lapalma
• 3849 Incidentia
• 3850 Peltier — Orbits within the Flora family region
• 3869 Norton
• 4188 Kitezh
• 4278 Harvey — Member of Baptistina family
• 4434 Nikulin
• 4796 Lewis
• 4977 Rauthgundis
• 5379 Abehiroshi

Middle and Outer Main Belt

Recent spectroscopic surveys have identified V-type asteroids throughout the main belt:^[21]

• Ten confirmed V-types orbiting in the middle main belt (2.5 < a < 2.82 AU)
• Five V-types in the outer main belt (a > 2.82 AU)
• Two V-types identified beyond 3.3 AU

Origin and Formation

Vesta Origin Hypothesis

The predominant theory suggests that most V-type asteroids originated as fragments of 4 Vesta's crust during large impact events.^[22] NASA's Dawn mission identified two enormous impact basins on Vesta's southern hemisphere:^[23]

• Veneneia basin: ~395 km diameter, formed approximately 2.1 billion years ago
• Rheasilvia basin: ~505 km diameter, formed approximately 1 billion years ago

These impact events excavated and ejected large amounts of basaltic material from Vesta's crust and upper mantle.^[24] The ejected fragments formed the Vesta family and are thought to be the source of the HED meteorites that fall to Earth.

Dynamical Evolution

V-type asteroids ejected from Vesta have undergone complex dynamical evolution:^[25]

• Fragments initially formed a collisional family near Vesta
• Yarkovsky effect and YORP effect caused slow orbital drift
• Interaction with mean-motion and secular resonances dispersed fragments
• Some fragments entered the 3:1 and ν₆ resonances, allowing delivery to Earth-crossing orbits

Multiple Parent Body Hypothesis

Recent research indicates that V-type asteroids in the middle and outer main belt are unlikely to have originated from Vesta.^[26] Extensive numerical simulations demonstrate the lack of efficient dynamical routes to transport Vesta fragments beyond 2.5 AU.^[27]

The asteroid 1459 Magnya provides compelling evidence for multiple differentiated parent bodies:^[28]

• Located at 3.14 AU, beyond plausible Vesta ejecta dispersal
• Spectroscopic differences from Vesta suggest distinct parent body
• May represent remnant of destroyed differentiated asteroid

Classification Methods

Photometric Identification

V-type asteroids can be identified through various observational methods:^[29]

• Visible photometry using SDSS filters (u, g, r, i, z)
• Near-infrared colors from 2MASS and WISE surveys
• Combined visible and near-infrared spectroscopy

Spectroscopic Confirmation

Definitive classification requires spectroscopic observations covering the 0.4-2.5 μm range to identify characteristic pyroxene absorption bands.^[30] Key diagnostic parameters include:

• Band I center position (0.90-0.94 μm)
• Band II center position (1.89-2.00 μm)
• Band area ratio (BAR = Band II area/Band I area)
• Spectral slope

J-type Subclassification

A J-type classification has been proposed for asteroids exhibiting particularly strong 1 μm absorption bands similar to diogenite meteorites, with Band I centers >0.95 μm.^[31] These objects likely sample deeper crustal or upper mantle material from differentiated parent bodies.

Notable Examples

4 Vesta

4 Vesta is the archetype of the V-type class and the only intact differentiated asteroid accessible to detailed study.^[32] Key characteristics:

• Mean diameter: 525.4 ± 0.2 km
• Bulk density: 3.456 ± 0.035 g/cm³
• Differentiated structure with metallic core (~220 km diameter)
• Basaltic crust thickness: 12–20 km

1459 Magnya

1459 Magnya represents the most significant non-Vestoid V-type asteroid:^[33]

• Semi-major axis: 3.14 AU
• Diameter: ~17 km
• Spectroscopic properties distinct from Vesta
• Possible fragment of destroyed differentiated asteroid

2579 Spartacus

2579 Spartacus shows unusual spectroscopic properties suggesting deep origin:^[34]

• Enhanced olivine content
• May sample mantle material
• Located at 2.71 AU

Significance

Solar System Evolution

V-type asteroids provide crucial constraints on early Solar System processes:^[35]

• Timeline of planetesimal differentiation (first ~5 Myr)
• Extent of igneous processing in the asteroid belt
• Number and distribution of differentiated parent bodies
• Collisional evolution of the asteroid belt

Meteorite Connections

V-type asteroids are the likely source of HED meteorites, providing ground-truth for asteroid composition studies.^[36] This connection enables:

• Laboratory analysis of asteroid material
• Calibration of remote sensing techniques
• Understanding of space weathering processes
• Chronology of asteroid belt evolution

Future Research

Ongoing and future research priorities include:^[37]

• Spectroscopic surveys to identify additional V-types
• Detailed compositional studies of non-Vestoid V-types
• Dynamical modeling of V-type distribution
• Search for olivine-rich V-types sampling mantle material

See also

• 4 Vesta
• Vesta family
• HED meteorites
• Asteroid spectral types
• Differentiated asteroids
• Dawn (spacecraft)
• Basaltic achondrites