LISA Pathfinder Test Mass (IMAGE) American Physical Society Caption Test masses carved from blocks of high purity gold-platinum alloy, and weighing nearly 2 kilograms, are flying aboard the LISA Pathfinder spacecraft in the development of systems that will detect gravitational waves as part of the forthcoming LISA space-based gravitational wave observatory. Credit European Space Agency, CGS SpA 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.