When the first close-up pictures of Pluto came in from the New Horizon satellite which flew by the planet this year, they shocked pretty well everyone who had thought about the now-demoted dwarf planet. Common sense suggested Pluto should be a frozen ball, with a pockmarked surface reflecting billions of years of Comet impacts. Instead what was revealed was a dynamic object, with mountains 3-4 kilometers high, and a huge 1000 km wide flat plain of ice with no impact craters. This means that this plain cannot be older than 100 million years old, implying that the surface of Pluto is dynamic. Since there are no other large planets nearby that might be sources of tidal heating, this means that Pluto still has an active internal engine, continuing to mold its surface. We have no idea how that could be the case.
Similar surprises have accompanied flybys of other solar system objects, from the liquid water ocean, and the organic-water geysers pushing through the surface ice of Saturn’s Moon Encedalus, to the surface full of volcanoes on Jupiter’s Moon Io. While these oddities are now understood to be powered by the huge tidal influence of the giant host planets, no one had expected this kind of extreme activity in advance.
As we peer out further to other stars we have found them to be ripe with planetary systems that were once thought to be impossible. Large gas giants like Jupiter and Saturn orbiting closer in to their stars than Mercury is to our Sun. It had previously been felt that inner planets would be small and rocky and outer planets larger and gaseous, as in our solar system. We now understand that dynamical effects may have caused large planets to migrate inwards over time in these systems.
Similarly, classical dynamics had suggested that binary star systems should not contain planets, as gravitational perturbations would expel such orbiting objects in a short time. But planets have now been discovered around even binary stars, suggesting some new stabilizing mechanism must be at work.
We are accustomed to recognizing that at the extremes of scale, the Universe is a mysterious place. For example, Dark Energy—the energy of empty space—appears to dominate the dynamics of the Universe on its largest scales, producing a gravitational repulsion that is causing the expansion of the Universe to accelerate. Or, on small scales, we currently have no idea why the newly discovered Higgs particle is as light as it is, one of the reasons the four forces in nature have the vastly different strengths we measure on laboratory scales.
But what we are learning as we explore even our own solar neighborhood, is that the physics governing the formation and evolution of nearby planetary-scale objects like Pluto, Io, and Enceladus—physics that we thought was well understood—is actually far richer and more complex than we had ever imagined. This not only brings the lie to claims made decades ago that physics was over, that no new results of relevance to understand human-scale physics would ever again occur, it also puts in perspective the hyperbolic claims made that a quantum theory of gravity such as the most popular candidate, superstrings or M-Theory, would be a Theory of Everything. While such a theory would be of vital importance for understand the origin of the Universe, and the nature of space and time, it would be irrelevant for understanding complex phenomena on human scales, like the boiling of oatmeal, or formations of sand on the beach.
While oatmeal and sand may not capture the public’s imagination, the exotic new worlds inside and outside our solar system certainly do. And our recent discoveries suggest that much conventional wisdom about even our nearest neighbors, and physics as classical as Newton’s, will have to be rethought. The result of such revisions will likely shed new light on vital questions including the big one: Are we alone in the Universe? It is hard to see how our cosmic backyard could get more interesting!