2014ApJ...781...25M

The near-Earth object (NEO) population, which mainly consists of fragments from collisions between asteroids in the main asteroid belt, is thought to include contributions from short-period comets as well. One of the most promising NEO candidates for a cometary origin is near-Earth asteroid (3552) Don Quixote, which has never been reported to show activity. Here we present the discovery of cometary activity in Don Quixote based on thermal-infrared observations made with the Spitzer Space Telescope in its 3.6 and 4.5 µm bands. Our observations clearly show the presence of a coma and a tail in the 4.5 µm but not in the 3.6 µm band, which is consistent with molecular band emission from CO₂. Thermal modeling of the combined photometric data on Don Quixote reveals a diameter of 18.4_–0.4^+0.3 km and an albedo of 0.03_–0.01^+0.02, which confirms Don Quixote to be the third-largest known NEO. We derive an upper limit on the dust production rate of 1.9 kg/s and derive a CO₂ gas production rate of (1.1±0.1)x10²⁶ molecules/s. Spitzer Infrared Spectrograph spectroscopic observations indicate the presence of fine-grained silicates, perhaps pyroxene rich, on the surface of Don Quixote. Our discovery suggests that CO₂ can be present in near-Earth space over a long time. The presence of CO₂might also explain that Don Quixote's cometary nature remained hidden for nearly three decades.