of exciting targets to explore and better understand planetary evolution and potential habitability.
The Jovian and Saturnian systems are effectively miniature planetary systems with disks of particles (rings) and a wide spectrum of satellites which have volcanic, tectonics, geyser-like, atmospheric and weather activities, among others. Europa and Enceladus seem to have subsurface oceans directly expressed in surface activities or morphology. Io has present volcanic activity that is reshaping its surface. Titan has a methane cycle similar to our planets’ hydrologic cycle and its North pole has numerous large lakes of hydrocarbon. Enceladus is ejecting water particles from its surface in a geyser-like fashion. We are truly having a first glimpse at a wide variety of other worlds. This was done with a small number of flyby and/or orbiting spacecraft which are the Lewis and Clark of the solar system. Over the next few decades we will be sending more sophisticated orbiters, balloons, landers, penetrators, submarines, and so on, which will explore in depth these new worlds.
Every time we send a mission to a new celestial object, we are surprised, and in the process gain new knowledge, be it from the analysis of the particles in comet tails acquired by Stardust, to the unexpected larger ejecta from Tempel 1 Deep Impact encounter. In addition to its eight planets (nine if you count Pluto), and their satellites, the solar system has thousands of small objects which can give us clues of how we came here. These includes active comets, main belt asteroids, dead comets, Trojan objects, Kepler belt objects, Earth crossing objects, and so on. With our technology we will be able to encounter, observe, land and possibly nudge some of these objects to better decipher the history of our solar system, and in some rare but important cases, avoid a major catastrophic impact.
Mercury, Venus, Uranus, Neptune and Pluto are also key pieces in the puzzle of the history of our