Fascinating Pluto

The special Physics Today issue on planetary diversity (April 2004) describes many fascinating objects in our solar system. But the controversy over Pluto’s planethood and the interest in new objects beyond Neptune shouldn’t mask the fascinating nature of Pluto itself. A recent consortium in which we participated used a total of nine telescopes, in Hawaii and California, to observe Pluto when it passed in front of a star. From the way the starlight faded, we could tell that Pluto’s atmosphere has expanded since it was detected in another occultation 15 years ago. From spikes of intensity in the fading starlight, we could even tell about kilometer-scale structure in Pluto’s atmosphere. We hope that the New Horizons spacecraft gets to Pluto before the expansion is inevitably reversed, which may cause the atmosphere to condense on the surface or freeze and fall as snow.

We are planning to observe more occultations by Pluto and other objects in the outer Solar System in the upcoming years. This effort often requires extensive international collaborations, so we would like to hear from others interested in collaboration. Large telescopes are not required for observing the brighter occulted stars.