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 CO _ { 2 } .
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 ^ { +0.02 } _ { -0.01 } , 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 ^ { -1 } and derive a CO _ { 2 } gas production rate of ( 1.1 \pm 0.1 ) \cdot 10 ^ { 26 } molecules s ^ { -1 } .
Spitzer IRS spectroscopic observations indicate the presence of fine–grained silicates , perhaps pyroxene rich , on the surface of Don Quixote .
Our discovery suggests that CO _ { 2 } can be present in near–Earth space over a long time .
The presence of CO _ { 2 } might also explain that Don Quixote ’ s cometary nature remained hidden for nearly three decades .