Key challenges and perspectives

Whether the Solar System can serve as a template for the typical planetary systems in general remains one of the fundamental questions of astronomy. Radial velocity surveys have been very successful in finding planets unlike the ones in our Solar System and are now reaching sensitivity and temporal coverage to detect Jupiter-like planets on Jupiter-like orbits. Giant planets on orbits 4 AU are found around 6% 

3 Transition from protoplanetary disks to debris disks 

Observations of the first 10 Myr of disk evolution have shown more dramatic changes than during the entire remaining lifetime of the systems. Not only is the disk material lost and the disk structure flattens, but the dust grain population, too, 

Multiple lines of evidence exist for a population of live radionuclides, such as 26Al or 60Fe, which were injected into the proto-solar cloud or disk prior to the formation of CAIs (e.g. Tachibana et al. 2006). Isotopic abundances suggest that the isotopes have originated in a supernova, possibly with a very massive star progenitor that also underwent a Wolf-Rayet phase (Bizzarro et al. 2007). If this interpretation is correct, the Sun must have formed in a very rich and dense stellar cluster, such as the Carina Nebula, very much unlike the Taurus or other low-mass star-forming regions. Luminous massive stars in such clusters may truncate or fully evaporate protoplanetary disks around other cluster members. Two key questions remain open. How close in time and space did the supernova explode 

Transient heating events were important in the formation of the Solar System and provided the energy to produce chondrules and refractory inclusions. These objects are not predicted in astrophysical models for the formation of planetary systems. They comprise 50-80% of the mass of many primitive meteorites. However, the mechanism that produced the transient heating events is still unknown. Future work must focus on putting the details of the petrographic and chemical analysis of these rocks into an astrophysical and cosmochemical framework of Solar System formation. 

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