Balloon-based observations of stellar occultations Cathy Olkin Southwest Research Institute April 27, 2007

What is a stellar occultation? A stellar occultation is a planet passing in front of a star. This star light probes the planet’s atmosphere or ring system at a higher spatial resolution than available any other ways near Earth observations.

What science can be derived from this technique? -Sizes of asteroids or other airless bodies. KBOs in the future. -Discovery and kinematic models of ring systems - Discovery of the rings around Uranus - Improved kinematic models of ring systems HST FOC stellar occultation light curve of Saturn’s rings (Bosh, Olkin, French, Nicholson 2003)

What science can be derived from this technique? -Sizes of asteroids or other airless bodies - Discovery and kinematic understanding of ring systems - Discovery and characterization of planetary atmospheres R (km) v. T (K) R (km) v. dT/dr (K/km) dry adiabat

An example of how we do this now  We choose events with shadow paths goes over arid locations - severely limits possible events  Accurate, timely prediction critical for for success Pluto June 12, 2006

An example of how we do this now, cont.  Expensive to cover all these sites and ship portable telescopes. Pluto June 12, 2006

Predicted occultations More than half the events happen during daylight More than half the events happen during daylight More than half the events happen over the ocean or otherwise not amenable locations More than half the events happen over the ocean or otherwise not amenable locations

Other ways to make this measurement Advantages Advantages-mobile -above most weather Disadvantages Disadvantages -KAO de- commissioned -awaiting SOFIA -SOFIA will be a heavily desired resource - does not give multiple chords - does not give multiple chords

Our idea Deploy balloons out of an airplane traveling perpendicular across the shadow path

Advantages  Nearly global access  Day and night events possible Depends on background level Depends on background level  Multiple chords  Above clouds  Good seeing

Questions?  What is the background level at wavelengths of 8000 Angstroms at both day and night at ballooning altitude Impacts telescope aperture; payload weight; expense Impacts telescope aperture; payload weight; expense  Stability and telescope pointing  Feasibility of deploying from airplanes  Communications/Operations of multiple balloons  Cost per unit Balloon Balloon Instrumentation/Telescope Instrumentation/Telescope Campaign costs Campaign costs