Most of us grew up with a rather placid notion of the formation of our solar system: dust agglomerating into larger clumps, with an “ice line” forming the divide between the outer behemoths like Jupiter that we see today against the smaller, rockier bodies orbiting closer to our sun. Then astronomers began to find exoplanets multiple times the size of Jupiter—and generally far too close to their stars to fit within our tidy classical theories. Time for a rewrite of the textbooks.

In this issue's cover story, “Born of Chaos,” Konstantin Batygin, Gregory Laughlin and Alessandro Morbidelli trace that still evolving, new history of our stellar neighborhood: “a tale of wandering planets evicted from their birthplaces, of lost worlds driven to fiery destruction in the sun eons ago and of lonely giants hurled into the frigid depths of near-interstellar space.”

A different kind of materials construction is the subject of “A Cure for Africa's Soil.” John P. Reganold and Jerry D. Glover explain the mechanisms of soil degradation in sub-Saharan Africa. With some 220 million of the world's 800 million undernourished people living in the region, restoring soils is a top priority to improve crop yields. Just adding more fertilizer won't work and can even worsen the situation. Scientists now are looking to a solution called perenniation—in which perennial plants such as shrubs, trees or grasses are grown alongside crops. They help to supply carbon and nitrogen, and their roots hold the soil against erosion.

Researchers who have a strong desire to study something like agriculture might metaphorically say they want to “scratch an itch.” But scientists have had only a piecemeal understanding of how the annoying feeling itself actually arises. In “The Maddening Sensation of Itch,” Stephani Sutherland describes new insights into the causes of itch—some of the first since the molecule histamine was found to set off the sensation in the early years of the 20th century.

These investigations could lead to new treatments for itch that does not respond to antihistamines. The article discusses the way nerve cells detect the presence of itch-inducing substances and then send off signals, relayed all the way to the brain, that tell the body it's time to scratch. Sutherland also mentions why itching is contagious—perhaps explaining why I began feeling those irritating twitches along my arm about halfway through reading the article.