Chefs have long used a simple trick to differentiate between a raw and hard-boiled egg. By spinning an egg and watching how it behaves when the spin is disrupted, it's easy to tell whether its interior is solid or liquid.
Applying a similar test to the planet Mercury, astronomers have found strong evidence that the planet closest to the sun has a fluid core. The research, led by Jean-Luc Margot, assistant professor of astronomy at Cornell, appears this week on the Web site of the journal Science.