Scientific Questions

A number of results published in recent years gave us a better insight on the processes that shaped our Solar System at its beginning: the JEB scenario (Turrini, Magni & Coradini 2011, Turrini, Coradini & Magni 2012), the collisional erosion of planetary embryos (Svetsov 2011), the "Grand Tack" scenario (Walsh et al. 2011) and the new crystallization ages of the diogenites (Schiller et al. 2011). In addition to this, the Dawn spacecraft reached Vesta on July 2011 and started its investigation of the asteroid, soon producing two important results: the confirmation of the spectral link between Vesta and the HED meteorites (Coradini et al. 2011b) and the assessment of the surface age of Vesta (4 Ga) according to the cratering record on the asteroid (Neukum et al. 2011), which can imply that the first 0.5 Ga of the history of Vesta cannot be probed through crater counting. However, the same results opened up a new series of questions about our understanding of the sequence of events that took place across the first 10 Ma of the lifetime of the Solar System. If the interpretation of the diogenitic data by Schiller et al. (2011) is correct, how could Vesta cool down and solidify in a few Ma when heat conduction would require an order of magnitude longer to solidify the interior of the asteroid? Does this imply, as Schiller et al. (2011) suggested, that the diogenites do not come from Vesta but from some now lost planetesimal of similar composition, as advocated also to explain the V-type asteroids not dynamically linked to Vesta and the different O isotopic ratios of HED meteorites (see e.g. McSween et al. 2011)? Or has something been overlooked at while studying the thermal evolution of Vesta? Radiometric ages of eucrites (Bizzarro et al. 2005) and the recent confirmation of the spectral matching between Vesta and the HED meteorites by the Dawn mission (Coradini et al. 2011b) support the idea that Vesta was among the first objects to form and differentiate into the Solar System. If so, as we discussed in the previous section, it is likely that Vesta underwent the bombardment caused by the formation of Jupiter. How did this affect the collisional record on Vesta? Can the techniques and the assumptions used to study the collisional evolution of the Moon and other planetary bodies, that formed at some later time and did not undergo the JEB, be applied nevertheless on Vesta or we are going to introduce some systematic error in the interpretation of the data? Why does the cratering record on Vesta not allow us to probe to times earlier that 4 Ga ago (Neukum et al. 2011)? What was the timescale on which volcanism took place on Vesta? How likely were impact-triggered volcanic phenomena across the JEB? Are there surviving signatures of the JEB on Vesta (cryptomaria, large effusive phenomena, eroded basins)? Finally, can the information on the surface composition of Vesta and the estimated erosion caused by the JEB be used to constrain the evolution of Jupiter and the early Solar System? Can we use the JEB scenario and the Dawn mission to assess whether Jupiter formed in the outer Solar System, outside or near to its present orbit, or if Jupiter formed somewhere nearer to the Snow Line and the inner Solar System like suggested by Walsh et al. (2011)? These are the main questions that we plan to address across this project.