Statistical analysis of the spectral properties of V-type asteroids: A review on what we known and what is still missing

Abstract

In recent years several small V-type asteroids have been identified in the main belt. Most of them belong to the Vesta's dynamical family (“Vestoids”) but an increasingly large number appears to have no link with it (“non-Vestoids”). V-types have also been found within the population of Near Earth Asteroids (NEAs) and they are linked to the Howardite–Eucrite–Diogenite meteorites (HEDs). Several questions on Vesta, the V-types, and the HEDs are still unsolved. Among them, probably the most important is whether all basaltic objects do come from Vesta or not. To help answer to this and similar questions, recent studies have focused on the analysis of the visible-near infrared (Vis-NIR; 0.4–2.5 μm) spectroscopic and mineralogical properties of large samples of V-types. The objectives are to highlight similarities and differences among V-types belonging to different subclasses, increase the number of available Vis-NIR spectra for under numbered subclasses, and compare these spectra with laboratory data. In this last case, we also considered the data from ion irradiation experiments performed on different samples of Eucrites, to simulate the effects of space weathering. The data analysis shows that although most of the V-type asteroids in the inner main belt do have a surface composition compatible with an origin from Vesta, this seems not to be the case for V-types in the middle and outer main belt (MOVs). For these asteroids, a number of physical and dynamical parameters point to an origin other than Vesta. The space weathering effects are evident for all V-type subclasses, except for the V-type NEAs where they are only moderate. In this case, the laboratory experiments support the idea that the current NEAs spectral properties could be due to a balance between space weathering and rejuvenative processes triggered by close encounters with terrestrial planets. Finally, we have applied the same Vis-NIR analysis to all HEDs with available spectra in the RELAB database, including those Eucrite meteorites which present anomalous oxygen isotopic composition and/or petrologic characteristics when compared to the rest of the HEDs. These “anomalous” Eucrites show some Vis-NIR differences with respect to the rest of Eucrites. This is an interesting point to be further investigated once more spectra of anomalous HEDs will be available.