Spitzer's stellar work
In the News Feature "After Hubble" (24 April, p. 388), D. Clery inappropriately characterizes the Spitzer Space Telescope as "now largely blind." In fact, Spitzer is alive and well and continuing to make substantial contributions to the advancement of astrophysics and to scientific preparations for the James Webb Space Telescope (JWST). The exhaustion of Spitzer's cryogen in mid-2009 left the observatory with two functioning imaging arrays at wavelengths of 3.6 and 4.5 µm. The performance of what is now called "Warm" Spitzer at these wavelengths matches that achieved during the cryogenic mission. Despite its small size, Spitzer is by far the most sensitive telescope, space or ground, available at these wavelengths. The science community has used Warm Spitzer for important scientific investigations, including studies of exoplanets, the early universe, variable stars to define better the cosmic distance ladder, clusters of galaxies, near-Earth asteroids, and comets. Spitzer remains very much in demand; for the past 2 years, the oversubscription for requested observing time has been the highest of the mission.