Exoplanet mass revealed in light
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2013/12/ag_planetmass_feat.jpg?fit=860%2C460&ssl=1)
PLANET PROFILER The final three mirrors of the James Webb Space Telescope’s 18 arrived at NASA’s Goddard Space Flight Center in Greenbelt, Md., on December 16. Thanks to a new technique, astronomers should be able to determine exoplanets’ masses after the telescope launches in 2018.
Chris Gunn/GSFC/NASA