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. These asteroids comprise approximately 6% of main-belt asteroids and are characterized by their basaltic surface composition, making them distinct from other asteroid types.

Characteristics

Physical Properties

V-type asteroids are relatively bright objects with moderate to high albedo values typically ranging from 0.20 to 0.40. 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.
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. 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:
  • 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. The ratio of Band II to Band I depths 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. The pyroxene composition is typically low-calcium pyroxene with varying amounts of high-calcium pyroxene. The visible and near-infrared spectra of V-type asteroids closely resemble those of basaltic achondrite meteorites, particularly the HED meteorites.
Spectroscopic analysis has revealed compositional variations among V-types:Eucrite-like: High calcium content, consistent with basaltic eucrite meteoritesDiogenite-like: Low calcium content, consistent with orthopyroxenitic diogenite meteoritesHowardite-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. The Vesta family is one of the largest asteroid families with more than 15,000 known members. Spectroscopic studies indicate that approximately 85% of the members of the Vesta dynamical family are V-type asteroids.

Mars-Crossing V-types

Several V-type asteroids have been identified as Mars-crossers, including:
Recent systematic searches have confirmed three additional V-type asteroids in the Mars crossing region through spectroscopic observations.

Near-Earth V-types

Several V-type asteroids have been identified among Near-Earth objects:
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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. As of current surveys, 22 V-type asteroids have been identified outside the Vesta family in the inner asteroid belt:809 Lundia — Orbits within the Flora family region956 Elisa — Located near 2.4 AU1459 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 body2113 Ehrdni2442 Corbett2566 Kirghizia2579 Spartacus — Contains a significant portion of olivine, which may indicate origin deeper within a differentiated body than other V-types2640 Hallstrom2653 Principia2704 Julian Loewe2763 Jeans2795 Lepage2851 Harbin2912 Lapalma3849 Incidentia3850 Peltier — Orbits within the Flora family region3869 Norton4188 Kitezh4278 Harvey — Member of Baptistina family4434 Nikulin4796 Lewis4977 Rauthgundis

Middle and Outer Main Belt

Recent spectroscopic surveys have identified V-type asteroids throughout the main belt:
  • Ten confirmed V-types orbiting in the middle main belt
  • Five V-types in the outer main belt
  • 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. NASA's Dawn mission identified two enormous impact basins on Vesta's southern hemisphere:Veneneia basin: ~395 km diameter, formed approximately 2.1 billion years agoRheasilvia 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. 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:
  • 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. Extensive numerical simulations demonstrate the lack of efficient dynamical routes to transport Vesta fragments beyond 2.5 AU.
The asteroid 1459 Magnya provides compelling evidence for multiple differentiated parent bodies:
  • 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:
  • Visible photometry using SDSS filters
  • 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. Key diagnostic parameters include:
  • Band I center position
  • Band II center position
  • Band area ratio
  • 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. 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. Key characteristics:
  • Mean diameter: 525.4 ± 0.2 km
  • Bulk density: 3.456 ± 0.035 g/cm3
  • Differentiated structure with metallic core
  • Basaltic crust thickness: 12–20 km

1459 Magnya

1459 Magnya represents the most significant non-Vestoid V-type asteroid:
  • 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:
  • 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:
  • Timeline of planetesimal differentiation
  • 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. 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:
  • 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