Juno spat in the face of certain death this week as it made its first and closest pass to the clouds on Jupiter. We don’t really think of spacecraft as being “disposable” per se, but we did sort of send a one-time-use spacecraft to Jupiter; even though it was specifically built so that it could handle Jupiter’s radiation belts, Juno won’t survive its mission there. You might even say that Juno will die for our wins.
It’s all because of the extreme electromagnetic environment around Jupiter. Liquid metallic hydrogen circulating in Jupiter’s interior contributes to the strength of the magnetic fields forming a deadly donut around Jupiter’s equator (we think; Juno is designed in part to confirm or correct this hypothesis). During the time it spends in orbit – about a year and a half – the spacecraft will swoop in for a close flyby above the planet’s cloud tops every 14 days. But that means every two weeks it has to make a deep sortie into – and back out of – the Jovian magnetosphere. Jupiter’s radiation belts extend out some 400,000 miles from the surface. Juno will skim within 3100 miles of the clouds, and this first close pass got within 2400 miles. While the stalwart spacecraft will make the shallowest possible passes through Jupiter’s magnetic field, damage from the repeated plunges will eventually fry it. All by itself, the magnetic flux is enough to induce electrical current sufficient to short out our best electronics and baffle Juno’s magnetometer. Then there’s the ionizing radiation. Jupiter is a terribly hostile place, and Juno is already committed. It completed its first orbit just this week.
It’s not like we didn’t realize the dangers of orbiting Jupiter. Juno was purpose-built for the ludicrous EM environment around Jupiter – it’s what happens when your tank (finally!) gears up like a tank.* It’s got a 10mm titanium “radiation vault” designed to mitigate damage from the particles accelerated by Jupiter’s insane magnetic fields. The spacecraft is swathed in those shiny thermal blankets, which in this case also act as a Faraday cage, allowing electricity to be diverted around Juno instead of building up a dangerous charge. It’s got a duplicate of everything important, because the project team assumed that at some point, components would inevitably short out and die. All its cords and cables are clad in braided metallic shields. And its polar orbit was planned to keep it in the most clement parts of the magnetosphere.
Every time it makes a new orbit around Jupiter from here on out, Juno will make a deeper and more perpendicular pass through the radiation belts, exposing its sensitive memory and control equipment to greater and greater doses of radiation. NASA hopes to get 36 orbits out of Juno before the radiation environment finally makes a TKO. Juno’s radiometer might only make it through 11 orbits, but JunoCam could kick it in eight or less. Either way, Juno will soldier on until it’s reached the end of its mission, and then de-orbit – which is to say, it will burn up in Jupiter’s atmosphere rather than risk contaminating Europa with Earthly microbes. But until then, Juno is “firing on all cylinders” and making data transfers back to Earth right on schedule.
“We are getting some intriguing early data returns as we speak,” said Scott Bolton of the SwRI, principal investigator on the Juno team. “It will take days for all the science data collected during the flyby to be downlinked and even more to begin to comprehend what Juno and Jupiter are trying to tell us.”
Images from JunoCam should be released over the next couple of weeks. Those images will include the highest-resolution views yet of the Jovian atmosphere and some beauty shots of Jupiter’s north and south poles. Scientists hope to use Juno’s camera and other instrumentation, including its magnetometer and the JEDI and JADE instruments, to learn more about what goes on around the poles, with an eye to the way the magnetic field interacts with Jupiter’s atmosphere, and especially its auroras.
Beyond the auroras, though, what we’re really after is a better sense of the internal structure of Jupiter. It was the first planet to form in our solar system, and whether or not it has a core will tell us how it formed, and could divulge important information about the formation of planets, our solar system and other star systems, and maybe even shed light on the conditions that led to the emergence of life on our own rocky little planet.
“We are in an orbit nobody has ever been in before,” said Bolton, “and these images give us a whole new perspective on this gas-giant world.”
*No offense is intended to tanks, especially those long-suffering paladins who build just fine but then can only facepalm as they watch their DPS charge blithely onto the point of an opponent’s sword.