The proton (red) (IMAGE) University of Bonn Caption has a radius of 0.84 femtometers (fm). Also shown in the figure are the three quarks that make up the proton and the gluons that hold them together. Credit Image: Dr. Yong-Hui Lin/University of Bonn Usage Restrictions This image may be used together with the press release. License Original 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.