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NASA

For the Juno spacecraft scientists on Wednesday it was the best of times, it was the worst of times, it was the age of discovery, it was the age of disquiet, it was the spring of hope, it was the winter of despair. We could go on as Dickens might, but the point is that on Wednesday scientists who sent the probe to Jupiter had both exciting scientific news, as well as some health concerns with the spacecraft.

First, the bad news. Late last week mission managers canceled a planned engine firing to drop Juno into a shorter orbital period around Jupiter, from 53 days to 14 days. As they were checking out the spacecraft's propulsion system, the mission scientists noted that two helium check valves that play an important role in the firing of the spacecraft's main engine did not operate properly. They decided to delay the burn until at least December, but they still intended to take advantage of this week's close approach to Jupiter by taking additional data.

Safe mode

However on Tuesday evening, shortly before Juno's perijove in its 53-day orbit around the planet on Wednesday, the spacecraft entered into a "safe" mode for an unknown reason. The Juno mission's principal investigator, Scott Bolton, explained during a news conference Wednesday that, "The spacecraft is like a smart robot, and it detected a condition that was not expected." So it turned off its science instruments to protect them as it flew through Jupiter's radiation belts.

Everything, however, is probably just fine with the spacecraft, Bolton said. As Juno is now flying away from Jupiter in its elongated orbit, mission managers have time to assess the situation. During the coming days they will analyze and understand what caused Juno to enter its safe mode and then address the issue. They also will look at the valves and the propulsion system, and determine when it is safe to fire the Leros 1b engine to drop into a 14-day orbit.

If for some reason the propulsion system is beyond repair, Juno can still fulfill its scientific mission with the longer 53-day orbits. The spacecraft's components should be fine during the extended time, and Juno won't be subject to any additional radiation—which is what scientists are most concerned about in terms of wear and tear—as it will spend the majority of the longer orbit far away from Jupiter. One concern is that after 20 of these 53-day orbits, in the middle of 2019, Juno might find itself eclipsed by Jupiter for longer periods of time due to orbital dynamics. This would pose a problem to the spacecraft as it is powered by solar energy. But 20 orbits is plenty of time to do the mission's primary science.

When asked about the worst case scenario for Jupiter, Bolton smiled. "The worst case scenario is that I have to be patient, and get the science slowly. The science opportunities are all there, and we'll have more time to analyze and interpret the science. But I have to wait, and I'm generally impatient, and most of my science team are."

Oh, the storms

Bolton also shared some insights about the science data collected by its first close pass of Jupiter, 53 days ago, when it flew over the planet's poles. As previously reported, Juno found no hexagon-shaped patterns in the upper atmosphere, like astronomers have found on Saturn. But they did find an awful lot of storms, many more than exist near the planet's equator. "That was kind of a surprise," Bolton said.

One highlight came when scientists looked at the terminator, the division between the parts of Jupiter illuminated by the Sun, and those in the dark. There they observed a cyclonic storm some 7,000km across, more than half the size of Earth. And because of its proximity to the terminator they could observe a shadow cast by the cyclone, and found that it rose 85km above the planet's atmosphere. "It is a truly, towering beast of a storm," Bolton said.

For the first time scientists also got a look inside the gas giant. Using Juno’s Microwave Radiometer, scientists could see a few hundred kilometers into Jupiter’s atmosphere, and found that its belts and bands apparent on the surface also extended in similar patterns well below the surface. They are only beginning to understand what this data means.