Two dedicated NASA missions are drawing strong interest towards this new category of Solar system object, created by the IAU only in 2006.
The Dawn mission, after having visited the asteroid (4) Vesta for approximately one Earth year, is now orbiting the dwarf planet (1) Ceres. Dawn has enabled for the first time a close-up view of the two biggest bodies of the asteroid belt. The New Horizons mission, on the other hand, had just a fleeting encounter with its target, Pluto and its planetary system, but its remarkable batch of data has already radically altered our view of the most prominent member of the Kuiper Belt.
William McKinnon describes the milestones of the Dawn and New Horizons missions and the importance of dwarf planets for the understanding of the Solar System in his commentary published by Nature Physics, available for free for a limited time.
Just before Dawn's arrival at Ceres, ground-based observations performed by M. Küppers and collaborators, in a study published in Nature, present evidence of water vapour around Ceres, which they attributed to outgassing from some locations on the surface. The paper is complemented by its News & Views. This hypothesis was spectacularly confirmed by Dawn.
The polygonal structures observed in some regions of Pluto by New Horizons has immediately attracted attention, as they can indicate the presence of convection. This hypothesis has been analyzed and confirmed by a pair of papers published in Nature. The first, by Trowbridge et al., presents the evidence that convection is indeed the mechanism generating the polygons. The second by McKinnon and co-authors models the physical conditions that could match the observations. The related News & Views highlights the meaning of these studies for Pluto's geologic processes.