New Horizons flew 7,750 miles from Pluto on July 14, 2015

NASA’s New Horizons made the first flyby of Pluto at 11:49 UT on July 14, 2015, passing about 7,750 miles (12,500 km) above the surface and about 17,900 miles from its largest moon, Charon. It had launched on January 19, 2006, and covered roughly three billion miles to get there.

How close, exactly?

You will also find 4,800 miles (7,800 km) quoted for the closest approach, and that number still appears on NASA’s own New Horizons mission page. The two groups that actually ran the encounter disagree with it: Johns Hopkins APL, which built and flew the spacecraft, and Southwest Research Institute, which led the science, both give 7,750 miles, or 12,500 km. We use their figure.

The aiming was extraordinary. SwRI reported that the spacecraft reached closest approach about one minute earlier than predicted at launch, threading a target window 36 by 57 miles wide, which it likened to an airliner arriving within the width of a tennis ball. A gravity assist at Jupiter in February 2007 added about 9,000 mph and cut three years off the trip.

During the flyby New Horizons pointed its instruments at Pluto rather than its antenna at Earth, so controllers heard nothing. At more than 30,000 mph, a particle the size of a grain of rice could have disabled it. Confirmation came about 13 hours after closest approach, at 00:53 UT on July 15, as a 15-minute burst of status messages.

Sending the science home was slower still. With Earth about 4.5 light-hours away and a transmitter managing only 1–2 kilobits per second, the full 6.25 gigabytes took more than 15 months, finishing in October 2016. By then the craft was heading for a second target: it flew past the Kuiper Belt object Arrokoth on January 1, 2019, the most distant object ever explored up close.