Science & technology | The New Horizons mission

Pluto’s icy mountains

At last, a mysterious dwarf planet is ready for its close-up

“WE ARE outbound from Pluto.” So said Alice Bowman, mission operations manager for New Horizons, an American space probe, when her charge resumed contact with Earth following its passage by the place on July 14th. After nine and a half years of its being inbound to Pluto, her announcement was met with jubilation. On July 15th the craft sent back the first hints of what it had seen as it whizzed by at 14km a second. Even these preliminary data are filled with mysteries that will take years to unravel.

Pluto is, on first blush, unlike any single world yet seen in the solar system. Instead, it is a composite of many of them—with mountain ranges more than 3km high. These are altitudes that suggest the crust of frozen nitrogen and methane on Pluto’s surface must be supported by ice, which is much stronger.

What is most surprising, as the image shows, is how unmarked by meteorite impacts Pluto is. Some geological process must be refreshing its surface. That requires amounts of heat that no geophysicist would have guessed Pluto had going spare. Far from being a dead, icy world, Pluto has proved itself a very lively one.

New Horizons also snapped pictures of Pluto’s five moons, including the largest, Charon (which also looks unpocked), and Hydra (which seems composed mostly of ice). There is much, much more to come. But it will come slowly, at rates no faster than 4 kilobits a second (a fourteenth as fast as an old-fashioned telephone modem). The full complement of fly-by data will take 16 months to relay—first as compressed files over a couple of weeks, just in case something should go awry, and then, slowly, in their fullest glory. The images released this week are a mere whetting of scientific appetites.

This article appeared in the Science & technology section of the print edition under the headline "Pluto’s icy mountains"

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From the July 18th 2015 edition

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