This unusual patient was an early version of the star tracker aboard NASA’s Juno spacecraft. Becker and other engineers had entered around midnight, long after the Curie Institute’s normal business hours, to get a taste of what the satellite will face when it arrives at Jupiter on July 4.
“It’s kind of like cat burglars in the middle of the night, stealing electrons,” said Becker, the lead engineer for the mission’s radiation monitoring experiment at NASA’s Jet Propulsion Laboratory.
It’s not your typical test for spacecraft parts, but this is no typical destination.
On Monday night, if all goes as planned, Juno will complete its 1.8-billion-mile journey and slip into Jupiter’s embrace — the first spacecraft to orbit the gas giant in more than a decade. Launched in 2011, Juno will fly within 2,600 miles of the planet, closer than any previous satellite. As it completes 37 orbits over 20 months, Juno will have to withstand a brutal onslaught that will deliver more radiation than 100 million dental X-rays.
“Jupiter is really, really hazardous,” said Scott Bolton, Juno’s principal investigator at the Southwest Research Institute. To withstand the barrage of high-energy electrons, most of Juno’s electronics are inside a titanium vault. “We’re an armored tank.”
The rewards of such a perilous mission are clear: to probe Jupiter’s deeply held secrets and solve major mysteries about the origins of our solar system, of Earth and, by extension, of life itself.
Like its mythological counterpart, Jupiter is king of its realm: the largest and most powerful planet, more than twice as massive as all the others combined, and the first to be born from the swirling disk of gas and dust that once surrounded our nascent star.
It is also the most sun-like planet: made mostly of hydrogen and helium, with traces of heavier elements thrown in. In fact, size aside, the main difference between Jupiter and the sun is that the planet has a larger share of those trace elements, including carbon, nitrogen and sulfur.
“We don’t know how Jupiter got enriched, but we know it’s very important,” Bolton said. “Because the stuff that Jupiter has more of is what we’re all made out of. It’s what the Earth is made out of. It’s what life comes from.”
Four centuries ago, Galileo Galilei’s observations of the planet and its four largest moons demonstrated that the Earth was not the center of the universe — a discovery that ultimately landed him under house arrest until his death. And yet, large as this storm-eyed, striped giant looms in our minds, we know remarkably little about it.
For example, scientists don’t know if Jupiter’s Great Red Spot, that giant storm that’s roughly twice the size of Earth, is merely an atmospheric phenomenon or a structure that penetrates far into the planet.
Nor do they know how much oxygen or water lies within the planet, a mystery that only deepened after NASA’s Galileo probe plunged into the gas giant in 1995 and found it to be surprisingly dry.
Hydrogen is by far the most abundant element in the universe, and oxygen ranks third. Together, that should have made for a lot of water — that is, if Jupiter really does hold within it the secret recipe for our solar system.
Perhaps the Galileo probe did not reach deep enough. Perhaps it hit a dry spot. Or perhaps scientists’ theories of planetary formation are completely wrong.
“That one single number, the water content, will tell us a whole lot,” said Steven Levin, Juno’s project scientist at JPL in La Cañada Flintridge.
Juno will also be the first mission to orbit the planet’s poles, documenting its powerful northern and southern auroras, studying its colossal magnetic field up close and perhaps learning what exactly powers it. After completing its nearly 5-year journey from Earth, the spacecraft will take a highly elliptical orbit, crossing from one pole to the other in just two hours, then shooting far out into space for about two weeks. This will allow researchers to compare their measurements close to and farther from the planet’s influence.
The deepest mystery lies at the heart of the gas giant — scientists want to find out whether it has a hard center, like an inverse Tootsie Pop. Researchers aren’t sure if Jupiter hides a solid core of heavy metals such as iron and nickel, or whether it’s filled with hydrogen that has been compressed so much that its electrons have been squeezed off, allowing it to behave like a metal. If there’s rocky material in the core, it may hint that Jupiter formed later in the solar system’s history, after chunks of rock had time to coalesce out of the dust.
Juno is a giant spinning three-armed pinwheel whose 30-foot-long solar panels make it about the size of a basketball court. So far from the sun, those panels only provide roughly 500 watts of power — not enough to power a hair dryer, but perfect for this efficient suite of instruments.
Among them: an infrared spectrometer, an ultraviolet spectrograph, a visible-light camera, a magnetometer and a plasma-wave sensor. It has a microwave sensor to search for water and ammonia hidden beneath the thick cloud-tops. Another sensor will map the planet’s interior structure by measuring the tiny shifts in radio signals caused by subtle gravitational tugs that distort the spacecraft’s orbit.
Unlike many NASA missions, Juno’s 20-month investigation probably won’t be extended by much: The spacecraft, armored as it is against Jupiter’s harsh environment, can’t protect its systems indefinitely. And scientists do not want to risk having a radiation-fried satellite go off course and potentially contaminate a nearby moon like Europa, one of the solar system’s best candidates for finding microbial life.
Ultimately, Juno will plunge into Jupiter’s atmosphere, succumbing to the punishing forces within.
The end may be a tad bittersweet for such a groundbreaking mission, said Rick Nybakken, Juno’s project manager at JPL.
“We all feel that way,” he said. “But we also know we’ve got a lot ahead of us.”
