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Overcoming considerable odds, NASA’S spacecraft arrived safely and manoeuvred into the gas giant’s orbit.
After a tricky journey whose success was far from guaranteed, NASA’S Juno spacecraft is now orbiting Jupiter. On the evening of 4 July PDT, it braved one of the most extreme environments in the solar system to skim within 5,000 kilometres of the giant planet’s cloud tops, firing its main engines to brake just enough to put it in the desired orbit.
“After a 1.7-billion-mile journey, we hit our burn within one second on a target that was just tens of kilometres large,” says the mission’s project manager Rick Nybakken of NASA’S Jet Propulsion Laboratory in Pasadena, California. “That’s how well the spacecraft performed tonight.”
“We conquered Jupiter,” added Scott Bolton, the mission’s principal investigator.
Although the spacecraft’s engines had been fired two times previously for mid-course corrections, this was the burn that had the scientists and engineers biting their nails.
That’s because it had to be conducted within Jupiter’s intense radiation belts, which could interfere with Juno’s electronics, causing its engines to misfire and the spacecraft to veer off course.
NASA even had a backup plan – if the engine unexpectedly shut down, the probe’s computer would reboot as quickly as possible in an effort to restart the engine to keep the probe from whizzing past Jupiter into interplanetary space.
Another risk was that the spacecraft might hit a fleck of dust as it zoomed between Jupiter and the inner reaches of its rings. “Even a small piece can do serious damage,” Bolton said, adding that the engine nozzle was particularly vulnerable because it had a protective coating that might get chipped, interfering with the engine’s ability to burn properly. But none of this happened. The burn started on time and lasted within one second of its target time. “It was a song of perfection,” Nybakken said.
An hour later, the spacecraft passed its last test by rotating from its deceleration orientation back into one in which its solar panels were again turned towards the sun – critical for a solar-powered craft.
“As soon as we turn away from the sun, a time clock starts,” Bolton said. “The whole game is to get turned back to the sun before you run out of battery.”
The spacecraft is now in a 53-day orbit. Its next close pass of Jupiter will occur in late August. During that pass, Juno will scout for unexpected issues, then fire its engine again to descend into a 14-day orbit, from which it will repeatedly swing by Jupiter over the next year and a half.
That late-august passage will be the first time Juno returns data about the giant planet’s near environs. On its first pass, the flight crew wanted to make sure that the only computer systems active were those that were absolutely necessary for the critical braking manoeuvre. “So all of the science [was] turned off,” Bolton said.
Once it begins, some of the mission’s research will focus on understanding Jupiter’s atmosphere. But the primary goal will be to see what Jupiter can reveal about the dawn of the solar system, and what Bolton calls the “recipe” for both the formation of our own solar system and ones we’ve discovered around other stars.
“Jupiter has a unique position in that recipe because it was the first planet to form,” he says.
Part of that recipe will be determined by using Juno’s instruments to find out how much water is contained in Jupiter’s upper atmosphere – an important marker of how far from the sun Jupiter was when it formed.
Another will come from Jupiter’s gravity field – does it have a rocky core? If so, Bolton says, that means it formed after rocky materials began to form in the disc of gas and dust surrounding the infant sun.
All of that, he adds, helps us understand our own origins.
“Jupiter sucks up the majority of the leftovers,” Bolton says. “We are the leftovers of the leftovers.”
In other words, Juno’s successful arrival at Jupiter might ultimately help us understand ourselves.
“By studying Jupiter,” Bolton says, “what you’re really learning is the history of the elements that eventually made us.”
THE PRIMARY GOAL WILL BE TO SEE WHAT JUPITER CAN REVEAL ABOUT THE DAWN OF THE SOLAR SYSTEM.