Poster Presentation
ALMA Study of Atmospheric Compositions of Jovian Moons Io and Callisto
Presenter: Ming-Chi Chung (National Taiwan Normal University)
According to the Grand Tack (GT) model, Jupiter is believed to have migrated very close to the Sun. Hence atmospheres of the four Galilean moons were largely destroyed during the GT due to non-thermal XUV-driven atmospheric escape. However, scarce atmospheres remain existent on Galilean moons today. It is thus important to study the chemical compositions of these atmospheres in order to understand their origins. In particular, by probing atmospheric trace components evaporated from the surface, we may infer the likely chemical compositions of the subsurface oceans suspected to exist on the outer three Galilean moons Europa, Ganymede and Callisto. Thanks to the high sensitivity and spatial resolution of the ALMA array, we are now able to resolve the discs of Galilean moons directly. As first steps, we use the archival ALMA data to study the atmospheric compositions of Io and Callisto, respectively, the innermost and outermost Galilean moons orbiting around Jupiter.
Because of its closeness to Jupiter, Io is the most geologically active body in the solar system. Io’s surface appears mainly in yellow, black, white and orange colors due to sulfide compounds ejected from volcanic eruptions. Sulfide compounds from volcanic plumes are also present in Io’s atmosphere. On the other hand, Callisto is about 1,880,000 km away from Jupiter, hence it is least affected by Jupiter tidally among four Galilean moons. Unlike Io, Callisto’s atmosphere is thought to be formed mainly due to sublimation of icy volatiles on its surface. Preliminary results obtained from our high spectral resolution ALMA study indicate the existence of sulfide compounds (SO, SO2 and 34SO2) and potassium chloride (KCl) in Io’s atmosphere. A hint of likely existence of ethanol in Callisto’s atmosphere is seen but it requires observations of more C2H5OH transitions for confirmation.
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