On July 4, late in the evening, NASA’s Juno spacecraft finally reached Jupiter, five years after the probe left Earth.
“Juno, welcome to Jupiter,” a voice announced at NASA, as the room of engineers and astronomers broke out into cheers and applause.
The solar-powered spacecraft, roughly the size of a basketball court, overcame the extraordinary challenges of its long journey and inhospitable destination to successfully enter a 53-day orbit of the gas giant 540 million miles from home.
Its mission: uncover the secrets lurking under Jupiter’s clouds.
Could our solar system’s largest planet be hiding a solid metal core? Significant amounts of water? The keys to understanding the origins of our solar system, Earth, and the ingredients needed for life itself? Scientists think these are all serious possibilities.
To get close enough to Jupiter to get the answers, Juno first had to make it through massive belts of radiation and storms of charged particles. It also had to slow down quickly and precisely enough to hook into Jupiter’s orbit rather than careening right past it, as Nadia Drake explained at National Geographic.
It also had to avoid engine failure, computer failure, and tiny particles of dust that could throw its equipment off completely. And then it had to flip around back toward the sun, so it could collect enough solar energy to continue its mission.
The danger is not yet over. Over the course of its 20-month mission, Juno will be exposed to unpredictable storms, high pressure, and the amount of radiation in 100 million dental X-rays.
But if Juno lives up to expectations, it will totally change our view of the solar system.
While probes have passed near Jupiter before, this mission will get closer than ever before, giving us our best chance to peer beneath its thick, stormy atmosphere — and understand what lies beneath. (Juno is in fact named for a Greek goddess, also known as Hera, who could see through clouds.)
The final view captured by Juno before its non-essential instruments powered down to prepare to enter Jupiter’s orbit. It was still 3.3 million miles away from its destination.
Juno looks like a three-pronged propeller, thanks to the unfurled solar panels that are powering it. The propeller spins three times every minute.
While it orbits Jupiter, it will keep the propeller’s edge toward the planet, like someone doing a string of cartwheels. The whole system makes Juno more stable, keeps the solar panels in the sun’s path, and lets all the instruments on board take turns to get a good look at Jupiter.
About those solar panels: this is the farthest away from the sun that NASA has ever been able to send a solar-powered spacecraft. (The New Horizons spacecraft currently studying Pluto, for example, runs on plutonium.)
Juno’s path around Jupiter was carefully calculated to keep it safe from the worst of the planet’s very strong radiation. Still, it’s a bit of an experiment in understanding how to protect instruments from damaging radiation, something we’ll need to get better at the more we want to leave Earth. Engineers designed from scratch a vault to protect the computers and other instruments on board.
It wouldn’t be a NASA mission without the promise of beautiful images. Nicknamed Juno Cam, the spacecraft’s camera will photograph the tops of the clouds masking the planet. But the radiation will get to Juno Cam pretty quickly — scientists only expect it to last for seven of the spacecraft’s 32 planned orbits of Jupiter.
Jupiter’s auroras, shown here in purple as seen by the Chandra X-Ray Observatory superimposed on a Hubble Space Telescope portrait of the planet.X-ray: NASA/CXC/SwRI/R.Gladstone et al.; Optical: NASA/ESA/Hubble Heritage (AURA/STScI)
One of the instruments on Juno, called JADE (short for Jovian Auroral Distributions Experiment) will be studying Jupiter’s huge polar auroras, which can stretch up to tens of thousands of kilometers.
JADE, with the help of a few other instruments, will tally up how many electrons and charged particles (and what kind) are creating the auroras. That should help scientists understand what causes them.
Meanwhile, instruments tracking the planet’s gravity are what will help scientists determine whether Jupiter is all gas or has a solid core buried down there.
That answer, plus how much water Juno finds in the planet’s atmosphere, will help scientists figure out if any one of their theories on how the planet formed is actually correct.
Because Jupiter is so huge (more than twice as large as all the solar system’s other planets combined), its gravity was strong enough to keep everything that was around when the planet formed, unlike smaller planets which lost lightweight gases. That means Jupiter is a bit like a time capsule that lets us see back to what our neck of the woods was like when the solar system first formed.
When Juno is done with its mission, it will dive towards the center of Jupiter and be destroyed by the planet’s atmosphere. But it has a lot of work to do before then. It’s not sending any scientific data back yet (its observation equipment was powered down so it could use all its energy to just get into the planet’s orbit), but July 4 marked a critical first step.
In due time, Juno’s principal investigator Scott Bolton promised, “We will have spectacular discoveries.” For now, he congratulated his team on “the hardest thing NASA’s ever done — or at least, that’s what I say.”
