VACUUM ATTRACTION Fleeting electromagnetic waves nudge parallel plates together through a phenomenon called the Casimir effect, illustrated here. If the same thing works with gravitational waves, it could prove the existence of particles that transmit gravity.
Emok/Wikimedia Commons (CC BY-SA 3.0)
TIGHT FIT The star Kepler 11 (illustrated) is home to six planets, five of which would fit inside the orbit of Mercury. Most solar systems might form with planets squished even closer together.
Tim Pyle/NASA
Two bright patches on the dwarf planet Ceres, seen in this image from the Dawn spacecraft, might result from ice volcanoes.
JPL-Caltech/NASA, UCLA, MPS, DLR, IDA
