A Disruptive DiskOur solar system makes makes a leisurely circuit every 250 million years around the galactic disk (above) of the Milky Way. But the route is not straightforward; our sun dips in and out of the disk every 30 million years. Biologist Michael Rampino at New York University speculates that this passage may be related to mass extinctions on Earth—like the one that wiped out all dinosaurs except for birds 65 million years ago. Cometary impacts are one explanation, among several, scientists use to explain these mass extinctions.

Disruptions—such as those caused by passing stars—in the Oort cloud, a debris field in the outer reaches of our solar system, can propel comets toward Earth. Rampino now believes that dark matter can also rattle this cloud every time our solar system wanders through the galactic disk.

—By Jane J. Lee, photo gallery by Nicole Werbeck

Photograph by Royal Academy Sciences

Week's Best Space Pictures: A Giant Erupts, a Glacier Spills, and Janus Hovers

A volcano awakens after seven years, a river of ice and snow spills onto a plain, and a Saturnian moon hovers near some rings in this week's best space pictures.

Published February 22, 2015