Last but not least are the observations of solar system objects. As with Astro-1, the dynamic processes occurring in the Jovian system (Jupiter and its moons) will be a primary target for HUT. These include the moon Io, the torus of plasma surrounding Io's orbit, the planet itself, and the polar aurorae. The UV emissions from all of these sources are time variable, and are related to one another, at least indirectly. In addition, the separation in time between Astro-1 and Astro-2 is sufficiently large to show possible secondary differences in the state of the Jovian system due to the 11 year solar cycle. (We are close to the minimum of the solar activity cycle now, whereas we were near the maximum back in late 1990.) The HUT wavelength coverage and resolution are almost ideal for this project, which is a favorite of HUT payload specialist Sam Durrance.
In addition, HUT scientists plan to observe Venus toward the end of
the Astro-2 mission. Venus is somewhat closer to the sun than the
Astro telescopes are normally pointed, but not dramatically so, being
near 40 degrees away. (The telescopes were pointed about 40
degrees from the sun once on Astro-1, to observe a comet, with no ill
effects.) Investigators will search for emission from various
molecular species that are excited by incoming solar radiation and
particles, as well as evidence of trace constituents such as the noble
gases argon and neon.