NASA’s Juno spacecraft prepares for cosmic date with Jupiter

LOS ANGELES — A solar-powered spacecraft is spinning toward Jupiter for the closest encounter with the biggest planet in our solar system.

NASA’s Juno spacecraft fires its main rocket engine late Monday to slow itself down from a speed of 150,000 mph (250,000 kph) and slip into orbit around Jupiter. With Juno on autopilot, the delicately choreographed move comes without any help from ground controllers.

The spacecraft is traveling through a hostile radiation environment and rings of debris and dust, “making for very serious hazards,” Juno chief scientist Scott Bolton said during a morning briefing. But Juno should be able to withstand the harsh conditions because it’s “built like an armored tank,” he said.

The spacecraft’s camera and other instruments were switched off for arrival, so there won’t be any pictures at the moment it reaches its destination. Hours before the encounter, NASA released a series of images taken last week during the approach, showing Jupiter glowing yellow in the distance, circled by its four inner moons.

Scientists have promised close-up views of the planet when Juno skims the cloud tops during the 20-month, $1.1 billion mission.

The fifth rock from the sun and the heftiest planet in the solar system, Jupiter is what’s known as a gas giant — a ball of hydrogen and helium — unlike rocky Earth and Mars.

With its billowy clouds and colorful stripes, Jupiter is an extreme world that likely formed first, shortly after the sun. Unlocking its history may hold clues to understanding how Earth and the rest of the solar system developed.