Studying these rifts is almost impossible. They have no mass, but can be located through fractured light from the other side. They are bound to a medium-strength centre of gravitational attraction, such as a planet, and will move with that body while they last. It seems they cannot live past twenty four hours, but sometimes even less than that. However, Rifts often reopen after their closure.
They are the entrances of tunnels through the Crossverse. An object entering one almost instantaneously appears at the other side, and so do air, light, radiation, and heat. Tunnels are of multiple sizes, most commonly 3m across, and spherical.
These Rifts usually connect planets with similar properties. It is theorised that microbes travelling through have seeded life on other worlds. However, planets with drastically different conditions can be majorly affected by these links.
There have been examples of Rifts connecting to stellar surfaces or protoplanetary disks. The reasons for this are unknown.
In the Crossverse
Rifts to birthing universes produce Rift-Stars, which survive far longer than conventional Rifts (up to millions of years). In the Crossverse, Rifts can be seen opening as far as the eye can see.