A FROST on Pluto’s moon Charon is an unexpected sign that the satellite is not completely dead. Mike Brown of the California Institute of Technology in Pasadena has obtained the first detailed infrared spectrum of Charon and found the crystalline form of ice. The spectrum also showed that ammonia was mixed with the ice (Science, vol 287, p 107).
Crystalline water is not stable at Charon’s frigid temperatures of around -223°C, and ammonia ices decompose when exposed to cosmic ultraviolet radiation. The two types of ice indicate that the surface of the moon is being continually reworked, says Brown,…
