interval

“Space Your Studies” In order to remember things for a longer time, repeat the material in spaced intervals.

At 20 minutes 8 central time, Professor Farrell of the Mount Jennings Observatory, Chicago, Illinois, reports observing several explosions of incandescent gas occurring at regular intervals on the planet Mars.

and Don Pettit, an astronaut, his theory is that, that low pressure zone starts to suck material away from the outside perimeter, breaking up the ring into regular intervals.