Juno enters Jupiter orbit

While America watched fireworks on the Fourth of July 2016, the people who most needed the night to go right were sealed in a windowless room at NASA's Jet Propulsion Laboratory. Juno, launched on 5 August 2011 and nearly five years and 2.8 billion kilometres into its journey, was diving toward Jupiter at one of the highest speeds any human-made object had reached, threading a gap between the planet and its lethal radiation belts. At 8:18 p.m. Pacific time, right on schedule, its main engine lit.

The 35-minute burn had to happen entirely on the spacecraft's own initiative. Juno spun itself up to five revolutions per minute for stability, turned its antenna away from Earth, and slowed by 542 metres per second while its makers listened to faint telemetry tones arriving 48 minutes after the fact. At 8:53 p.m. Pacific time the tone confirming capture arrived, and the room at JPL erupted. A spacecraft running on sunlight 25 times weaker than Earth's had put itself into polar orbit around the largest planet in the Solar System.

Everything about Juno was an engineering dare. It was the first solar-powered spacecraft sent to Jupiter, flying three nine-metre solar wings to harvest a few hundred watts. Its computers ride inside a titanium vault because Jupiter's radiation would otherwise destroy them, and bolted to its deck are three aluminum LEGO figurines: the god Jupiter, his wife Juno, and Galileo, who discovered the planet's large moons in 1610.

Settled into long 53-day polar orbits, Juno proceeded to rewrite the textbook. Its instruments revealed geometric clusters of cyclones at both poles, a surprisingly deep Great Red Spot, a lumpy magnetic field, and gravity data pointing to a strange, dilute core, while JunoCam's images, processed by volunteers around the world, became some of the most recognizable planetary photographs ever made. Extended well beyond its planned end, the mission went on to fly past Ganymede, Europa and Io, operating through September 2025 and beyond its original imagination.