Cracked Mud (IMAGE) Duke University Caption As a volume of mud dries, its internal tension grows until it suddenly cracks hierarchically, meaning with a few large cracks along with many small ones. A similar process is responsible for the wide variety of sizes that celestial bodies come in, according to a Duke professor. Credit Adrian Bejan, Duke University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.