As far as puny former planets go, Pluto is definitely one weird little world. Since New Horizons’ close encounter with the distant dwarf planet last July revealed a jagged, diverse terrain littered with canyons, mountains and hills of nitrogen-ice, scientists have been mesmerized by photos of the unimaginably complex world.
Now, with months of data still left to downlink back to Earth, scientists have formally started telling the story of a world that was once the ninth planet of our solar system. On Thursday, five new studies were published in the journal Science, providing a detailed analysis of Pluto's landscape, atmosphere, moons, chemistry, and its interaction with solar wind.
“These five detailed papers completely transform our view of Pluto – revealing the former ‘astronomer’s planet’ to be a real world with diverse and active geology, exotic surface chemistry, a complex atmosphere, puzzling interaction with the sun and an intriguing system of small moons,” Alan Stern, New Horizons principal investigator from the Southwest Research Institute, Boulder, Colorado, said in a statement.
Many of the findings are related to the dwarf planet’s atmosphere. For the first time, scientists have discovered a plausible mechanism that may be responsible for Pluto’s atmospheric haze. This mechanism involves the concentration of particles by buoyancy waves, or “gravity waves” — not to be confused with gravitational waves — created by winds blowing over Pluto’s mountainous topography.
“For several decades, telescopic observations have shown that Pluto has a complex and intriguing atmosphere. But too little has been known to allow a complete understanding of its global structure and evolution,” the researchers wrote in one of the studies.
It turns out that Pluto’s upper atmosphere is much colder — by about 70 degrees Fahrenheit — than previous, Earth-based studies had indicated. Why this is so remains a mystery.
“We’ve discovered that pre-New Horizons estimates wildly overestimated the loss of material from Pluto’s atmosphere,” Fran Bagenal, from the University of Colorado, Boulder, and lead author of one of the papers, said in the statement. “The thought was that Pluto’s atmosphere was escaping like a comet, but it is actually escaping at a rate much more like Earth’s atmosphere.”
Another study reveals that Pluto barely interacts with solar wind — the high-energy stream of particles ejected by our sun. Analysis of data collected by New Horizons revealed that the “interaction region” between the solar wind and Pluto’s atmosphere is confined to the dayside of Pluto to within 6 Pluto radii, or about 4,500 miles — much smaller than expected before the flyby.
Scientists believe this is most likely due to the lower-than-expected atmospheric escape rate.
Scientists have also analyzed close-up images of Pluto’s small moons, Styx, Nix, Kerberos and Hydra, which range in diameter from about 25 miles for Nix and Hydra to about six miles for Styx and Kerberos. Some of these moons, it turns out, have highly “anomalous” orbits. They’ve also found evidence that some of the moons resulted from mergers of even smaller bodies, and that their surface ages date back at least 4 billion years.
So far, only half of New Horizons’ flyby data has been transmitted home. And it's expected that some of the best discoveries about Pluto's tiny, complex world are yet to be made.