Juno’s Close Encounter with Jupiter

Juno – a Jovian Boomerang

On 5 July 2016 a new NASA spacecraft called Juno arrives at Jupiter after five years of traveling the Solar System. Juno is set to peel back the layers of Jupiter to reveal its secrets, but first it has to survive a high-speed manoeuvre to enter into a stable orbit around Jupiter.

This manoeuvre, called Jupiter Orbit Insertion, occurs in the early hours of Tuesday 5 July (UK time) and will determine the whole success of the Juno mission. Gain too much speed and Juno will sling-shot around Jupiter much like the icy rocks that stray too close to Jupiter and are flung around the Solar System. Too little speed and Juno will fall towards Jupiter to burn up in its dense atmosphere.

“We go in sort of like a dive-bomber,” according to Dr Scott Bolton, a space physicist at the Southwest Research Institute who leads the science team for Juno. Speaking to Astronomy Now, Bolton says “We go in really fast and get out fast. That speed itself is really hazardous, and we’re also spinning. We’re this giant solar array spacecraft cartwheeling through this incredible magnetic field and radiation belt. It’s a little bit scary.”

Searching for Water

Why bother with such a risky mission? What can we learn about Jupiter that’s so important?

Water. We don’t know how Earth got its water, but it seems likely that Jupiter played a big role. In the early days of the Solar System, the Sun was surrounded by a giant disc of gas and dust, which gradually started collapsing into the planets we know today.

Near the Sun, hot temperatures and strong solar winds should have vaporised and blown away the liquid and icy water out to colder climates in the outer Solar System. Much of it is thought to have ended up in Jupiter, Saturn, and the other gas giants, as well as in the cloud of comets beyond Pluto.

So how did Earth end up covered in water? Without Jupiter, all the water in the outer Solar System may have stayed just there, but with Jupiter’s immense gravity tugging constantly on the icy comets, many could have been sling-shot back into the inner Solar System and landed on Earth, Mars, and other rocky planets, delivering water and organic materials onto newly-cooled worlds.

Juno will map the environment around Jupiter, including its gravitational field, to uncover just how it redirects particles, meteors, and solar winds around the Solar System, and whether it ultimately plays a good or bad influence on the formation of life here on Earth.

Juno will also hunt for water inside Jupiter. Just like on Earth, astronomers think that a water cycle drives the weather and storms (such as the Great Red Spot) on Jupiter.

But the trouble is that so far we haven’t found enough water on Jupiter to prove this.

Juno carries a microwave camera that is specifically tuned to find any water underneath the top layers of Jupiter’s atmosphere, if it exists. Finding water means we can begin to explain the extreme weather patterns on Jupiter and perhaps even link it back to our own water cycle and weather here on Earth.

In preparation for Juno’s arrival, a new infrared map of Jupiter reveals glowing activity beneath the clouds. This ground-based image will support Juno’s data to reveal Jupiter’s complex weather.

Jupiter Detectives

Juno has several other cameras on board, tuned to frequencies of light that we can’t see. This allows them to measure things beneath the Jupiter’s clouds, like water content and temperature. Other detectors will measure Jupiter’s magnetic field (the strongest in the the Solar System after the Sun’s) and gravitational field (which will reveal the shape and density of Jupiter’s unknown core). A particle detector will sample the plasma that flows around Jupiter and causes its vibrant auroras.

But the astronomers who designed Juno felt that it would be a crime to send a spacecraft closer to Jupiter than ever been before and not include a camera that sees things as we would see it. And rightly so! JunoCam is the people’s camera, included to give us a sense of Juno’s perspective, to allow the public to control and select regions of Jupiter to photograph, and quite possibly to do some lucky science along the way. There is still so much that is unknown about Jupiter that it’s hard to say which Juno detector will reveal the most.

What is certain is that Juno will help us peer back to the beginning of our Solar System 4.5 billion years ago. “We like to call Jupiter a time capsule because it is so massive; all of the stuff that was incorporated into Jupiter when the planets first formed is not allowed to escape,” says Dr Leigh Fletcher, planetary scientist at the University of Leicester, speaking at the National Astronomy Meeting this week.