V-type asteroids, also known asVestoids, are a class ofasteroids whosespectral type is characterized by a strong absorption feature at wavelengths longward of 0.75 μm, similar to that of4 Vesta, the second-most-massive asteroid in theasteroid belt.[1] These asteroids comprise approximately 6% ofmain-belt asteroids and are characterized by theirbasaltic surface composition, making them distinct from other asteroid types.[2]
V-type asteroids are relatively bright objects with moderate to highalbedo 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.
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+ inpyroxene
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.
V-type asteroids are composed primarily of basaltic material containingpyroxene andplagioclase 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 basalticachondrite meteorites, particularly theHED 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
The vast majority of V-type asteroids are members of theVesta 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]
The predominant theory suggests that most V-type asteroids originated as fragments of4 Vesta's crust during large impact events.[22]NASA'sDawn 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.
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 asteroid1459 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
A J-type classification has been proposed for asteroids exhibiting particularly strong 1 μm absorption bands similar todiogenite meteorites, with Band I centers >0.95 μm.[31] These objects likely sample deeper crustal or upper mantle material from differentiated parent bodies.
^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.
