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]
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]
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]
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
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
^Usui, F.; et al. (2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117.
^Pieters, C.M.; et al. (1985). "The Nature of Asteroid 4 Vesta from Mineralogical Studies of the HED Meteorites". Journal of Geophysical Research. 90 (B14): 12393–12413. Bibcode:1985JGR....9012393P. doi:10.1029/JB090iB14p12393.
^Carruba, V.; et al. (2005). "On the V-type asteroids outside the Vesta family. I. Interplay of nonlinear secular resonances and the Yarkovsky effect: the cases of 956 Elisa and 809 Lundia". Astronomy and Astrophysics. 441 (2): 819–829. arXiv:astro-ph/0506656. Bibcode:2005A&A...441..819C. doi:10.1051/0004-6361:20053355.
^Carruba, V.; Michtchenko, T.A. (2007). "A frequency approach to identifying asteroid families II. Families interacting with nonlinear secular resonances and low-order mean-motion resonances". Astronomy and Astrophysics. 475 (3): 1145–1158. Bibcode:2007A&A...475.1145C. doi:10.1051/0004-6361:20077689.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Michtchenko, T.A.; et al. (2002). "Origin of the basaltic asteroid 1459 Magnya: A dynamical and mineralogical study of the outer main belt". Icarus. 158 (2): 343–359. Bibcode:2002Icar..158..343M. doi:10.1006/icar.2002.6871.
^Hardersen, P.S.; et al. (2018). "Basaltic asteroid (1459) Magnya: Possible fragment of Vesta or a distinct parent body?". AAS/Division for Planetary Sciences Meeting Abstracts. 50: 305.07. Bibcode:2018DPS....5030507H.
^McSween, H.Y.; et al. (2013). "Dawn; the Vesta-HED connection; and the geologic context for eucrites, diogenites, and howardites". Meteoritics & Planetary Science. 48 (11): 2090–2104. Bibcode:2013M&PS...48.2090M. doi:10.1111/maps.12108.
^Binzel, R.P.; et al. (2019). "Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS)". Icarus. 324: 41–76. arXiv:2004.05090. Bibcode:2019Icar..324...41B. doi:10.1016/j.icarus.2018.12.035.
