Adam Riess, Space Telescope Science Institute (STScI) astronomer and professor at the Johns Hopkins University is a newly elected Fellow of the American Academy of Arts and Sciences. The Academy honors excellence by electing to membership remarkable men and women who have made preeminent contributions to their fields, and to the world. Riess is a leader of a team that, in 1998 co-discovered "dark energy", a mysterious repulsive force in the universe. Dark energy is the biggest mystery now confronting astrophysics, and Riess continues doing observations to deduce what dark energy is. The 38-year-old astrophysicist has been at STScI since 1999.