Richard A Lovett
NASA’s Juno spacecraft is now successfully orbiting Jupiter. This afternoon, 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 by 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 the mission’s principal investigator, Scott Bolton.
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 in which, if the engine unexpectedly shut down, the probe’s computer would reboot as quickly as possible, in an effort to restart the engine quickly enough to keep the probe from whizzing past Jupiter into interplanetary space.
Another risk was that the fast-moving spacecraft might hit a fleck of dust as it passed 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.
The mission’s research will be focused on understanding Jupiter’s atmosphere. But the primary goal will be to see what Jupiter can teach about the dawn of the solar system.
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 toward 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, meaning it won’t make another close pass of Jupiter until late August. It will use that pass to 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 today’s 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 be focused on understanding Jupiter’s atmosphere. But the primary goal will be to see what Jupiter can teach 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 to 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.”
