Mercury Darkened by Carbon (IMAGE) Brown University Caption New research suggests that carbon from cometary material that bombards the Mercury may be the reason the planet's surface is so dark. Experiments show that impact material is significantly darkened when impacts occur in the presence of complex organics. Credit NASA/Ames/Brown Unviersity 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.