As we slide into another end-of-year holiday season, I’m thankful for a lot of things, from family and friends to a great new job at Ars. But I’m also thankful for New Horizons, the grand-piano-sized spacecraft that revealed Pluto to humanity for the first time this year. Anyone under about 45 years old, which narrowly includes me, largely missed the real-time excitement as the Voyager probes uncovered the Solar System’s outer worlds in the 1980s.
And what a discovery Pluto proved to be. Far from a cold, dormant, cratered world at the edge of the Solar System, Pluto dazzled with varied terrain and active geology. Perhaps most important, the tiny, almost-a-planet world reminded us all of what makes science so great and so rewarding. First comes the joy of discovery, and then a realization that with new information comes a multiplicity of questions.
For Pluto that has meant finding a world with a surface that yet lives. Part of the left side of its “heart,” known as Sputnik Planum, appears to be less than 10 million years old. Scientists had no notion they would find this smooth feature before New Horizons arrived in July. Now they are left scrambling to understand how this could be.
This week I met with Fran Bagenal, a planetary scientist whose 40-year professional career has allowed her to be involved with the Voyagers, NASA’s Galileo mission to Jupiter, the Cassini mission to Saturn, and now New Horizons. When it comes to exploring the outer worlds of the Solar System, she’s seen pretty much everything. And to be honest, Bagenal told me, she didn’t anticipate all that much from Pluto beyond an asteroid-like object.
“I was expecting a really, really boring little object covered by impact craters, something like a Vesta or Ceres, which wasn’t particularly interesting,” she said. “And instead we see all these weird things being moved around, like ice formations. It’s incredible.”
It has also raised questions about what may be driving the world’s active geology and the movement of water ice and nitrogen ice on its surface. Scientists are just now crafting theories and models to explain how much residual heat might be leaking from Pluto’s interior and how this could provide a small amount of warmth to the surface. But scientists must also consider a host of other factors, such as how do minute amounts of methane, carbon dioxide, and complex organic molecules like tholins change the viscosity of the ice? And what about the effect of the extreme cooling from above the surface? And how do cryovolcanoes fit in?
Scientists must also factor in Pluto’s eccentric orbit, ranging from 30 to 50 astronomical units from the Sun. Does this also play into the convective cycle? They must also consider whether Sputnik Planum looks so much different from the rest of Pluto because a comet or some strange Kuiper Belt object grazed the world there and splattered it with a lump of nitrogen.
To study unknown processes, scientists like to take data and make careful observations over time. But with Pluto they got a single snapshot. “I am afraid some of these things we’ll never know, and we’ll never sort them out,” Bagenal said. “So these are some of the scenarios going through people’s minds. I would never have imagined that was going to be the case with such a dynamic world.”
New Horizons collected all of this amazing data during a brief, hours-long flyby of Pluto, after taking nearly a decade to traverse more than 5 billion km of empty space. And that single view is all these scientists will get in their lifetimes, because it takes a long time to plan and build and fly these outer-worlds missions, and Pluto is unlikely to get back to the top of the exploration list any time soon.
In truth scientists have higher priorities, with a smorgasbord of mysterious worlds left to explore, such as Jupiter’s ice-covered ocean world of Europa, and Enceladus and Titan around Saturn. One has geysers shooting into space between ice cracks and the other oceans of methane. To say nothing of Neptune and Uranus, which we last visited when Bagenal was just a graduate student.
The Solar System is truly a wondrous place, and science gives us the tools to explore it in unprecedented ways. I am thankful to be alive at a time when we are finally doing so.
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