Nexus

The planet Nexus is somewhat larger than Earth, but due to being less metal-rich has almost exactly the same surface gravity. Nexus has generally infertile soil and few natural resources, and orbits the out-of-the-way star of Namepending; it would be wholly unremarkable if not for an unusual structure orbiting it. It is known, rather uncreatively, as Nexus I.

Every so often, Nexus I releases a pair of nickel-iron meteoroids. Invariably, one falls down to Nexus (and almost all the time within a relatively small region of the planet), and one is launched at another planet in the Solar System. On the outside, these meteoroids are merely an accessible source of high-quality steel; once the metal has been harvested, though, a ring of silicon carbide, of diameter 2.4 meters, is exposed. Each ring is linked to its mate in that anything that passes into one passes out the other; it is from this property, allowing low-tech travel across the Solar System via Nexus, that the planet gets its name.

The origins of Nexus I are completely unknown. It is obviously the product of advanced technology, given its ability to create hyperspatial portals with no apparent power or materials source. That vast amounts of energy are involved is clear due to the occasional explosion of a portal pair when monkeyed around with by the overly curious, and also by the routine disintegration of any probe that has attempted to visit Nexus I directly.