Scientists confirm closest known Earth-sized world, LTT 1445 Ac, orbiting a small red dwarf star just 22 light-years away. LTT 1445 Ac, an Earth analog, provides valuable insight into planet evolution and differences. Hubble Space Telescope helps obtain high-resolution measurement of LTT 1445 Ac's density, suggesting it is a rocky exoplanet similar in size and composition to Earth.