Search

We have observed the 2002 August 21 occultation by Pluto of theR ¼ 15:7mag star P131.1, using 0.5 s cadence observations in integrated white light with the Williams College frame-transfer, rapid-readout CCD at the 2.24 m University of Hawaii telescope. We detected an occultation that lasted 5 minutes, 9:1 � 0:7 s between half-light points. The ‘‘kinks’’ in the ingress and egress parts of the curve that were apparent in 1988 had become much less pronounced by the time of the two 2002 occultations that were observed, indicating a major change in the structure ofPluto’satmosphere.AnalysisofourlightcurvesshowsthatthepressureinPluto’satmospherehasincreasedatall the altitudes that we probed. Essentially, the entire pressure scale has moved up in altitude, increasing by a factor of 2 since 1988. Spikes in our light curve reveal vertical structure in Pluto’s atmosphere at unprecedentedly high resolution.Wehaveconfirmationofourspikesatlowertimeresolutionaspartofobservationsoftheemersionmade at 1.4 s and 2.4 s cadence with the 3.67 m AEOS telescope on Maui.

Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity. The Zodiac II instrument is a 1.1-m diameter SiC telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visiblewavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights within the United States followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.