Asteroid 4 Vesta: from Ground Observations to the Dawn Mission–Evolution of Concepts of Mineralogical Composition and Surface Structure

The paper presents a review of photometric and spectrophotometric observations of the asteroid Vesta (one of the largest asteroids in the Solar System) carried out by Kazakhstani astronomers in 1986–1988. As a result, these observations yielded important results, including the final confirmation of the actual rotation period of Vesta and the reliable recording of variations in the intensity of the core of the first absorption band of pyroxene in the spectrum of Vesta’s surface. An analysis of individual spectra obtained by us at different phases of Vesta’s rotation shows a tendency for the center of the first band to shift to the long-wave region of the spectrum with an increase in the depth of the band. These features can be interpreted as the presence of significant unevenness in the distribution of pyroxene over the surface of the asteroid, or as a result of the influence of the degree of maturity (age), or the fragmentation of the pyroxene-containing substance of a certain area on the asteroid as a result of impact. Estimates of the position of the “spot” or crater indicate that on the surface of the asteroid, the pyroxene spot is located in the southern hemisphere of Vesta and has a diameter of about 40° in the planetographic coordinate system and may have a higher Ca content. Peculiarities in the distribution of the mineral pyroxene on the asteroid’s surface suggested the presence of a large impact crater. This was confirmed by the discovery of such a crater in much later years through observations from the Dawn spacecraft (in 2011). Our results are also consistent with and complemented by other studies of Vesta in recent decades.