NASA’s Juno spacecraft went into safe mode last night, 13 hours before it swung close by the surface of Jupiter. Since July 4th, Juno has been in a highly elliptical orbit around the gas giant, swinging close by Jupiter every 53 days to take scientific measurements of the planet and its insides. But since Juno was in safe mode, all of the vehicle’s instruments were automatically turned off and were unable to collect any data during this most recent pass by the planet.

It "detected a condition that was not expected"

It’s unclear what caused Juno to go into safe mode, but NASA thinks it may be related to a software problem that caused the onboard computer to reboot. At a press conference today, Juno principal investigator Scott Bolton said the vehicle had "detected a condition that was not expected," but he did not think the problem was related to the radiation environment around Jupiter.

Whatever happened caused Juno to turn off all its "unnecessary subsystems" — including its science instruments — and point itself toward the Sun to get as much power as possible. It’s now awaiting further instructions from NASA on the ground. Bolton says the spacecraft is healthy, though, and the mission team is working to getting it back to optimal working conditions.

This marks the second road bump for Juno in the last week. On Friday, NASA announced that it was going to delay changing Juno’s orbit —a move that was supposed to happen today. When Juno passed by Jupiter today, NASA was going to ignite the spacecraft’s main engine, putting the vehicle into a shorter 14-day orbit around Jupiter. But the space agency decided to postpone that because a couple of valves in Juno’s engine didn’t behave as expected.

A composite image of cloud formation at Jupiter. (NASA)

Delaying the shift doesn't detract from the science that Juno can do at Jupiter; it just means the mission could take longer to pull off. Right now it takes 53 days for the spacecraft to complete one orbit and pass close by the planet — what is known as a perijove pass. That's the prime time for Juno to do its science at Jupiter. Staying in a 53-day orbit simply means those passes will happen less frequently. "The worst case scenario is I have to be patient and get the science slowly," Bolton said at the conference.

Still, the Juno team has two big problems to solve now: figuring out why the spacecraft went into safe mode and why the engine isn’t working like it should. But the mission has still led to some interesting discoveries about Jupiter in the meantime. Juno conducted its first perijove pass on August 27th with all of its science instruments on, and based on that data, NASA now knows that Jupiter's magnetic field and aurora are a lot bigger than originally thought. The pass also gave Juno its first peek underneath the surface of Jupiter, finding that the planet's clouds extend as far below as the spacecraft's instruments can see. And they are constantly changing the farther down they go. "It is as if we took an onion and began to peel the layers off to see the structure and processes going on below," Bolton said in a press release.