New Horizons flies past Pluto

In the early hours of 14 July 2015, the operations room at the Johns Hopkins Applied Physics Laboratory in Maryland was crowded, but the spacecraft everyone had come for was utterly alone. Four and a half light-hours from Earth, New Horizons was executing its encounter entirely by stored command, too busy gathering data to call home. At 11:49 UTC it swept within about 12,500 kilometres of Pluto's surface at nearly 14 kilometres per second, a one-shot pass at a world three billion miles away. There would be no second chance and no orbit, only a day of furious observation.

The journey had begun nine and a half years earlier, on 19 January 2006, when an Atlas V threw the piano-sized, 478-kilogram probe away from Earth faster than any spacecraft before it; it crossed the Moon's orbit in about nine hours. Seven months later, astronomers reclassified Pluto as a dwarf planet. New Horizons had left for the ninth planet and would arrive at something the textbooks no longer agreed on, which made the encounter feel less like a footnote and more like a verdict.

Just before 9 p.m. Eastern time that night, after an agonizing day of planned silence, a 15-minute status message arrived and the room erupted: the spacecraft had survived with its data intact. What followed astonished even the mission's veterans. Pluto's 'heart,' Tombaugh Regio, held Sputnik Planitia, a churning nitrogen-ice glacier roughly a thousand kilometres across, bordered by water-ice mountains rising as high as the Rockies. The supposed dead iceball was geologically alive.

The encounter's full harvest trickled home over 16 months through a radio link slower than an old dial-up modem, each image a small event in itself. New Horizons then flew on, and on 1 January 2019 it skimmed past the Kuiper Belt object Arrokoth, the most distant world ever explored up close. The spacecraft is still flying outward today, a working observatory in the Solar System's far suburbs.