This week we leave the familiar planets behind and venture into the farthest reaches of our Solar System, into regions where the Sun’s influence begins to fade and the boundaries of our cosmic neighborhood grow uncertain.

We explore the Kuiper Belt, a vast disk of icy remnants left over from the formation of the planets, and travel even farther into the mysterious Oort Cloud, a distant, spherical halo of objects that may extend halfway to the nearest stars. Along the way, we uncover the discoveries that reshaped our understanding of the Solar System, from the first detection of Kuiper Belt objects to the controversial reclassification of Pluto after the discovery of Eris.

We also follow the journey of the Voyager spacecraft, now drifting through interstellar space yet still deep within the Sun’s extended domain, and examine the ongoin ...