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The riddle posed by super-Earths (1-4$R_\oplus$, 2-20$M_\oplus$) is that theyare not Jupiters: their core masses are large enough to trigger runaway gasaccretion, yet somehow super-Earths accreted atmospheres that weigh only a fewpercent of their total mass. We show that this puzzle is solved if super-Earthsformed late, as the last vestiges of their parent gas disks were about toclear. This scenario would seem to present fine-tuning problems, but we showthat there are none. Ambient gas densities can span many (up to 9) orders ofmagnitude, and super-Earths can still robustly emerge after $\sim$0.1-1 Myrwith percent-by-weight atmospheres. Super-Earth cores are naturally bred ingas-poor environments where gas dynamical friction has weakened sufficiently toallow constituent protocores to merge. So little gas is present at the time ofcore assembly that cores hardly migrate by disk torques: formation ofsuper-Earths can be in situ. The picture --- that close-in super-Earths form ina gas-poor (but not gas-empty) inner disk, fed continuously by gas that bleedsinward from a more massive outer disk --- recalls the largely evacuated butstill accreting inner cavities of transitional protoplanetary disks. We alsoaddress the inverse problem presented by super-puffs: an uncommon class ofshort-period planets seemingly too voluminous for their small masses(4-10$R_\oplus$, 2-6$M_\oplus$). Super-puffs easily acquire their thickatmospheres as dust-free, rapidly cooling worlds outside $\sim$1 AU wherenebular gas is colder, less dense, and therefore less opaque. Unlikesuper-Earths which can form in situ, super-puffs migrated in to their currentorbits; they are expected to form the outer links of mean-motion resonantchains, and to exhibit greater water content. We close by confrontingobservations and itemizing remaining questions.

Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks