Scientists have released the first published scientific results from July's historic flyby of Pluto and its moons, highlighting new discoveries and the new mysteries that have arisen with those discoveries.
A new paper published in Science today by the New Horizons team, led by principal investigator Alan Stern, summarizes what scientists have learned from data collected by the New Horizons spacecraft during the first-ever flyby of the dwarf planet and its moons on July 14.
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Here are 3 mysteries they highlight.
What's reshaping Pluto's surface?
Pluto's surface is covered in a range of features from mountains to plains, and different kinds of ice that range from bright and shiny to very dark red in colour.
Some areas appear to be shaped by glaciers and by ice that vapourizes in some areas and redeposits in others, especially on the plains near the planet's equator.
The formation of mountains and other geological reshaping seems to have happened recently, puzzling researchers.
"This raises questions of how such processes were powered so long after the formation of the Pluto system," they wrote.
They note that on most other icy bodies in the solar system – mostly moons — that kind of reshaping is powered by tides that make certain regions bulge and create heat from friction during the motion.
"But these are not a viable heat source today for Pluto or Charon," the researchers added.
What's that dark spot on Charon's north pole?
Pluto's largest moon, Charon, is mostly pale-coloured, but there's "puzzling dark terrain" on its north pole.
One possible explanation scientists have come up with is that during colder times, gases deposit there, then radiation chemically transforms them into coloured compounds called tholins that are heavier and less likely to vaporize during warmer times.
Why are Nix and Hydra so bright and shiny?
Measurements show that two of Pluto's moons, Nix and Hydra, are covered by the ice we're most familiar with – frozen water.
That ice is unexpectedly clean and bright.
"How such bright surfaces can be maintained on Nix and Hydra over billions of years is puzzling," the researchers wrote.
Billions of years of radiation and impacts from darker material such a meteorites should have made them turn darker and redder over time.
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Another interesting discovery made by New Horizons but not mentioned in the new paper is that unlike Earth's moon – and likely most if not all other moons in the solar system – Nix and Hydra don't always face the same side toward Pluto.
"We now believe Nix and Hydra are spinning really fast and rotating in an odd way, and may be the only regular moons, meaning satellites that are near their host planets, which do not always point the same face toward their primary body," said Douglas Hamilton, a University of Maryland researcher who co-authored the new Science paper, in a statement.
That may be because of Pluto's largest moon Charon, which doesn't just orbit Pluto, but also has Pluto in its orbit, as a kind of "binary planet" system.
"It's possible that Nix and Hydra can't focus on locking one face toward Pluto because Charon keeps sweeping past and stirring things up."
New Horizons is still in the process of sending data from its flyby back to Earth, a process that will take nearly another year.