It’s obvious why NASA would spend decades and billions of dollars getting to Mars. Humanity is pretty attached to the idea that Mars is Earth’s slightly less hospitable cousin. Why getting all the way to Jupiter should be a priority is less clear. The planet is a storm-torn ball of poisonous gas—not exactly a great getaway destination.

But distant and deadly as it is, the red-eyed gas giant is exactly where NASA’s Juno mission is heading. After a nearly five-year journey, the unmanned, solar-powered Juno spacecraft should be going into orbit around Jupiter at around 11:15pm ET on Monday, July 4th, carrying an array of instruments that will do everything from analyzing fluctuations in Jupiter’s gravity to visualizing its magnetic field. It’ll snap some pretty pictures too, of course.

That is, provided that the tricky (but entirely automated) business of orbit insertion goes according to plan. Juno has one shot at syncing up with Jupiter’s gravitational pull. If the orbital maneuver is unsuccessful, there are no second chances—Juno will just sail on by. “Everything is riding on what happens July 4th,” says Scott Bolton, the Juno mission’s principal investigator. “I haven’t felt this way since launch. If something goes wrong, we’re not getting any science.”

And considering that Bolton and much of his team have been working on Juno for well over a decade, anything less than total success will be quite the blow. “I learned early in my career that in this field, you have to be patient,” Bolton says. “But Juno is different—I’m personally responsible for it all.”


The 49 minutes it will take for Juno’s message of success or failure to travel the hundreds of millions of miles between the spacecraft and Earth aren’t going to be easy. “I’m basically a nervous wreck,” says Candice Hansen-Koharcheck, senior scientist at the Planetary Scientist Institute and JunoCam lead. “Everything has to happen at once. It won’t be okay until it’s July 5th, and we can all stop hedging our bets.”

As gambles go, Juno is high stakes, and not just for personally invested scientists like Bolton and Hansen-Koharcheck. You should care: The data Juno gathers could lead to significant leaps in scientists’ understanding of not only Jupiter, but the entire solar system. And possibly of life itself.

The Road to Jupiter

Before thinking about answering any of those questions, the Juno team had to build something that could even get out there. “Everything about Jupiter is bigger and badder,” says Randy Gladstone, a planetary scientist and Juno’s UVS instrument lead. Jupiter has the strongest magnetic field in the solar system. It’s lethally radioactive. And it’s hella far from the sun. That all creates problems for scientific instruments and spacecraft—particularly a solar-powered craft like Juno.

Juno’s engineers needed to design a craft with instruments that can run on kitchen-appliance levels of power and withstand intense cold. “A solar panel in Earth orbit will get to 20, 30 degrees Celsius—kind of room temperature,” says Kevin Rudolph, a Lockheed Martin spacecraft lead systems engineer on the Juno project. “But around Jupiter, in sunlight, a solar panel will be at about -100 degrees Celsius.” Any liquids in Juno’s system (like the propellant they need for that all-important orbital maneuver) is in constant danger of freezing and bursting its pipes.

Of course, that’s all moot if the system gets fried by the time Juno arrives. Jupiter’s strong magnetic field means that any electrically conductive material that passes through it, including a metal-hulled spacecraft, is doing the deep space equivalent of shuffling its feet across a carpet and touching a doorknob. In general, electrical equipment like the computers that make up Juno’s brain don’t take kindly to arcs and sparks.

Or to bombardment by radiation, for that matter. “Radiation can refer to protons and electrons that are bumbling around like bees, going real slow and not very energetic,” says Rudolph. “That kind of shielding can be as simple as a piece of paper. On the other hand, you can have much higher energy particles, typical of Jupiter environment, and those take a lot more shielding.” That’s why Juno’s most delicate equipment is protected inside a titanium vault that distributes stray electrons evenly, and shields it from radiation.

There have been hiccups along the way—like in the spring of 2014, when Juno got slammed by a cosmic ray that blue screened its computers for a while—but those moments have just proved the strength of Juno’s self-correcting systems. “Our greatest accomplishment has been just designing and building Juno,” says Bolton.

The Origin of the Solar System

So far, that is. But that could change when Juno finally goes into orbit. The craft will ultimately make 37 close approaches, coming within 2,900 miles of the gas giant’s roiling clouds to take measurements. “There’s far more known than unknown,” Bolton says.

One thing scientists don’t know jack about: Jupiter’s auroras. A solid four instruments onboard Juno (WAVES, UVS, JADE, and JIRAM) are devoted to studying the excited particles around Jupiter’s poles, which are thousands of times larger and more powerful than Earth’s light shows. “By going to Jupiter and Saturn and other planets, we see a different set of variables, which we can’t get on Earth because we don’t have a good way to change our planet’s parameters,” says Bill Kurth, a research scientist at the University of Iowa Department of Physics and Astronomy and WAVES investigation lead. Juno’s instruments will study the particles causing the auroras and how they interact with Jupiter’s magnetosphere, telling them how and why Jupiter’s auroras have gotten so huge.

But NASA’s intrepid craft isn’t just there to stroke Jupiter’s ego. It’s also going to help scientists understand how this—the solar system, planets, life—all began. “If you want to understand the origins of the planets, including Earth, you have to start with Jupiter,” says Kurth.

The going theory is that the solar system pretty much started with Jupiter. Like the sun, it’s mostly hydrogen and helium—elements that are big components of a protosolar nebula. Scientists know that those lightweight leftovers tend to disperse quickly after the birth of a star, so it seems like Jupiter must have planetized really quickly.

Unlike the sun, though, Jupiter is enriched with heavier elements like carbon and nitrogen—and scientists don’t know how it got that way. Juno will determine whether Jupiter is also enriched with water (the Galileo mission didn’t detect any, but many believe it to have been an unlucky sample), and whether it has a rocky core. If the majority of Jupiter isn’t water depleted, then heavy elements probably arrived at the planet by way of ice—at some point, the planet got bombarded by a bunch of carbon-loaded space snowballs. But if Jupiter does have a rocky core of heavy elements, that must mean that those rocky substances formed before Jupiter did, maybe even before the sun.

“We know this is important because the stuff that Jupiter has more of, the heavy elements, is what life itself is made of,” says Bolton. “Understanding how Jupiter got that way, how it formed, how it started the enrichment process, is the smoking gun as to how we all got here.”

Humans will probably never set foot on Jupiter, let alone colonize it. Certainly nobody is ever growing potatoes there. But the things it has to tell us about our origins make it worth the trip, or at least sparing a thought for the room full of scientists who are spending their 4th of July agonizing over a tiny, basketball-court sized spacecraft almost 5 million miles from home.

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Juno’s Jupiter Mission Faces Its Most Critical Moment