Vision and Voyages for Planetary Science in the - Solar System ...

discoveries suggest such bodies may dominate the population of exoplanets, filling this gap in our
knowledge rates as a high priority.
New lessons from the inner solar system over the last few decades show it, too, is far more
complex and active than previously known—discoveries here are equally exciting. Venus may harbor
active volcanic eruptions issuing sulfurous compounds and water vapor to feed the sulfuric acid clouds. 84
Mars is also far more active than we earlier thought, with changes on the timescale of only a few years:
new impact scars, new landslides, and active processes occurring in gullies. 85 Time-lapse movies from
the Mars rovers show dust devils racing across surface. We have new evidence for glaciers on Mars,
extending even to the equator in places and active or recent subsurface processes, of hidden origin,
generating methane. Mars’s hydrothermal and volcanic activity likely extends through today but
confirmation will require seismic data, a critical area for future investigation. We have found strange
“active” asteroids in the main belt jetting dust and gas, behaving like comets. Once the Moon had global
oceans of molten lava, today its seismic tremors can elucidate its internal structure and yield secrets of its
early origin and evolution.
In summary, we have come full circle in our view of how complex, diverse, and often active the
processes that drive the solar system are. In the end, we have come to realize that as we explore, our
expectations commonly fall short of what nature has in store for us in the unknown reaches of the solar
system and the universe.
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