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V-type asteroid
From Wikipedia, the free encyclopedia
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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]
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Characteristics
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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
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Distribution
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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]
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]
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
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Origin and Formation
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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.
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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
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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
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See also
- 4 Vesta
- Vesta family
- HED meteorites
- Asteroid spectral types
- Differentiated asteroids
- Dawn (spacecraft)
- Basaltic achondrites
References
External links
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