As fireworks go bursting in air Monday night, deep-space monitoring stations will hold a silent vigil, straining to hear a beep from just outside Jupiter that signals Juno has arrived.
The Juno probe was launched in 2011 to study Jupiter, and on Monday NASA will find out if they hit their mark 1.8 billion miles later, or if they overshot. As it traveled around the solar system to Jupiter, Juno has been busy at work, even sending images of Jupiter back, but now it has gone quiet.
Entering the orbit of its destination planet is such a critical phase for the Juno mission that all of its sensors and other systems have been turned off to reduce the chances of anything going wrong. So it's only a simple radio signal that will indicate all is well, once Juno has arrived.
Juno is the first probe since the 1989 Galileo mission to specifically visit Jupiter. Other probes, including the recent Pluto probe New Horizons, have swung by Jupiter for a gravity assist or some snapshots, but they weren't designed to stick around and study Jupiter.
Juno has been painstakingly constructed to survive this extremely hostile space around Jupiter, referred to as Jovian space, to explore some fundamental questions about the planet and the origins of our solar system.
Why send a probe back to Jupiter?
We have many questions and few concrete answers about Jupiter.
While we have been able to see its Great Red Spot for centuries, what lurks below remains a mystery. Does Jupiter have a solid rocky core beneath the clouds somewhere? Or is it an ocean of metallic hydrogen all the way down? We don't know, but Juno is going to try to find out. NASA's asked Bill Nye to explain this part of the mission and how they plan to do it.
Jupiter is mainly composed of the same materials — mostly hydrogen and helium — as the early solar nebula that eventually created our solar system. By studying it, scientists hope to find some of those materials in their primordial form — in some ways, Jupiter's massive size has preserved it in its near-original state.
The Juno probe will measure the amounts of water, methane and ammonia in Jupiter's atmosphere, which will help scientists begin to better understand the planet's — and our solar system's — ancient past.
What's special about the Juno probe?
When the probe arrives in Jupiter's orbit, it will be the most distant solar-powered probe from the earth. According to NASA, Jupiter receives only 1/25th of the sunlight we receive here on Earth.If it were to orbit Earth, Juno's solar panels would be capable of producing 14 kilowatts of power.
Near Jupiter, those same panels will be working hard to produce the roughly 500 watts of power needed to run the probe. Previous probes to the outer planets — any of the planets beyond Mars — have been nuclear-powered.
Since Juno will be traveling in and out of the strongest radiation belts and magnetic fields outside of the sun, the probe will carry its electronics in a titanium vault to protect the most sensitive among them from the ravages of Jovian orbital space. Many of the sensors are much heavier than on other probe, thanks to this heavy shielding.
What happens on July 4?
In order to reach Jupiter in only four years, the probe gained a great deal of speed, even swinging by Earth in 2013 for a gravity boost. Now it needs to slow down, so it doesn't overshoot.
To slow down for what NASA calls the "Jupiter Orbital Insertion" on Monday night, (it's scheduled to happen shortly after 10 p.m. Central), the probe turns to point its main engine forward, and will fire it for 35 minutes to slow the speed of the craft enough that it gets caught in Jupiter's gravity well and is pulled into an orbit.
Over the next couple months, NASA scientists will make adjustments to put Juno in its planned orbital path. It's scheduled to dive down past the north pole of Jupiter and then back out away from the planet with each orbit.
At its closest point, Juno will soar a mere 3,100 miles over the tops of Jupiter's clouds, a great chance for some spectacular snapshots. This polar orbit takes Juno around the planet's radiation belts, but over the course of the mission the orbit will shift, sending Juno deeper through the belts to study them as the mission nears its end.
But what are radiation belts?
Jupiter has powerful magnetic fields surrounding it — the largest planetary fields in the solar system. Charged particles from the sun are trapped within these magnetic fields. They form radiation belts, like the Van Allen Belts of Earth, but much much more powerful. The radiation can damage the probe's sensors, computers and other systems, which is why this part of the probe's exploration is scheduled for the mission's end.
How long will we have Juno continue to fly around?
Designed to survive long enough to part the veil of the most hostile atmospheric and orbital environments in the solar system, the Juno mission will last for 37 orbits around Jupiter. All the while, it will be beaming data back to Earth, even during its final flight into the planet itself. On that last orbit, which is projected to end in February of 2018, the probe will plunge into Jupiter's atmosphere, just as Galileo did, to comply with NASA's planetary protection requirements.
NASA is bringing another of its big-name space probes in on the Jupiter fun. For the next month, the Hubble telescope will be making daily observations of Jupiter.