Pluto continues to puzzle and intrigue scientists as data and images flow back to Earth from NASA's New Horizons spacecraft, and the latest images have astronomer saying "it's the pits."
That's their response to images of the dwarf planet that show hundreds of deep pits scattered across the Sputnik Planum, the heart-shaped region scientist think is a huge depression on the surface filled with frozen gases, mostly nitrogen.
The images, gathered by the spacecraft's Long Range Reconnaissance Imager (LORRI) instrument and posted to a public website, show a pattern of clusters of small pits and troughs.
The researchers suggest the pits and troughs, some hundreds of meters across and probably tens of meters deep, may be the result of the sublimation or evaporation of the volatile ices on the surface that then reveals darker materials in the surface beneath.
Those ices covering much of Pluto's surface are likely only a "surface veneer" covering a widespread water-ice based bedrock veneer, they say.
As evidence they cite mountains on the dwarf planet that rise almost 2 miles above their surroundings. If those mountains were made of frozen ices of nitrogen, carbon dioxide or methane -- instead of bedrock -- they would collapse rapidly, the researchers explain.
"Pluto is weird, in a good way," says Hal Weaver, New Horizons project scientist with Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. "The pits, and the way they're aligned, provide clues about the ice flow and the exchange of volatiles between the surface and atmosphere, and the science team is working hard to understand what physical processes are at play here."
The pits are just one of the discoveries about Pluto presented in a study by the New Horizons team published [pdf] in the journal Science.
Astronomers think the surface at the Sputnik Planum is around 100 million years old, which makes the region much younger than other geological features seen in other regions of Pluto.
It is surprisingly free of any craters, compared to other areas of the dwarf planet's surface, suggesting that in at least some areas activity including ice flows, sublimation, internal convection and winds have all likely shaped Pluto.
"What's striking to me is that, yes, there is activity, but it's not everywhere and that's an interesting part of the puzzle," says astronomer Will Grundy at the Lowell Observatory, who leads the New Horizon surface composition team and co-authored the study.
"It's obviously a special place that doesn't fit into the pattern you see across the rest of the surface," says Grundy of the Sputnik Planum and its puzzling pits.
