NASA's Juno spacecraft to probe Jupiter for the secrets of our Solar System's Formation by Pecier Decierdo


This week, NASA's Juno spacecraft will perform a crucial move that will, if successful, insert itself into a very unique orbit around Jupiter. This maneuver, called a Jupiter Orbit Insertion, or JOI, will start at around 11:18 AM Philippine Standard Time on July 5, Tuesday.*

In one of the stories from Roman mythology, the god Jupiter hid himself behind clouds to cover his mischief. It was his wife, the goddess Juno, who was able to see through the clouds and discover Jupiter's secrets. 

As in the myth, the Juno spacecraft was designed to see through Jupiter's surface clouds to uncover the secrets hiding underneath.

Fig 1. Juno is set to see through Jupiter's cloud cover.
Image credit: NASA/JPL-Caltech.

What Jovian secrets is Juno trying to uncover?

Unlike the Earth and other rocky planets like Mars, the gas giant Jupiter does not have an actual surface to speak of. The rich tapestries of colors you see when looking at pictures of Jupiter are bands and swirls of clouds. Underneath these clouds are denser bodies of fluid.

Juno wants to peer into these deeper layers to measure how much water there is in Jupiter. Most of this water would be in the form of water vapor. Measurements of the amount of water in Jupiter will give scientists clues about where and how this gas giant formed. 

Fig 2. Artist's conception of how the young Solar System looked like.
Image credit: NASA/JPL-Caltech.

Some scientists propose that Jupiter formed from far away, probably around where Uranus is now. According to these proposals, when the Solar System was just developing, a huge clump of ice formed far from the newly burning Sun. This ice core gathered much of the nearby gas to form Jupiter. Eventually, the newly formed gas giant would migrate to where it is now.

Other proposals suggest that Jupiter formed close to where it is at the present. In these proposals, Jupiter did not have to migrate over a long distance. According to such theories, Jupiter formed because instability within the cloud surrounding the young Sun caused the gas to collapse into gas giants, the biggest and most massive of which is Jupiter.

Knowing how much water there is in Jupiter will provide clues to help us figure out which of these proposals is closer to the truth.

Why is Jupiter's formation important? 

We know that Jupiter is the biggest planet in our Solar System, but just how big is it? Imagine putting together more than 1330 Earths. Jupiter would still be slightly bigger than that. This gargantuan planet is 2.5 times more massive than all other planets combined, making up more than 70% of the planetary matter in the Solar System. Basically, majority of the material left over from the forming Sun became what is now Jupiter.

Fig 3. The planets of the Solar System, to scale in size.
Image obtained via Wikimedia Commons.

How Jupiter formed is, therefore, important to our understanding of how the other planets, including Earth, formed. In a way, Juno is a mission to understand how we got here. 

Jupiter's great mass also creates a very strong gravitational pull that traps most of the original material. Hence, much of what makes up present-day Jupiter is original stuff from the formation of the Solar System.

Scott Bolton, Juno's principal investigator, described the mission's aim by saying: "What Juno is really about is learning...the recipe for how solar systems are made."

"We know after the Sun formed, something happened and we were able to form Jupiter. It took up more than half of the material that was left over. And it's a little bit different than the Sun, and we don't completely understand that. [It's] really the first step in making the recipe," Bolton said during a NASA press conference about the mission. 

Aside from looking through the surface clouds to measure the amount of water, Juno was also designed to detect the presence or absence of a solid core inside Jupiter. Planetary scientists have long debated whether Jupiter has a solid core in its very center, and if there is one, how big it is. Juno's measurements will lead us closer to the right answer.

Fig 4. One of the several models of Jupiter's interior.
Image obtained via Wikimedia Commons.

Is Juno going to have a breezy time around Jupiter? 

Certainly not. Scientists describe Jupiter as the 'biggest, baddest planet in our Solar System', which explains why it has the biggest, baddest magnetic field and radiation belt around it. This magnetic field traps a lot of highly energetic particles and radiation that can easily fry the equipment aboard most spacecraft.

Fortunately, Juno is not like most spacecraft. Most of Juno's scientific instruments will be protected by more than 180 kilos of thick titanium shielding. The spacecraft was designed to withstand the intense radiation so close to Jupiter. Scientists estimate that its electronic components will remain working for most of its nearly one and a half years of gathering data around Jupiter.

After its mission is done, Juno is set to crash into the clouds of Jupiter, eventually to be crushed by the titanic pressures there. Scientists fear that some hardy bacteria from Earth may have hitched a ride aboard Juno and might have survived the ravages of space and Jupiter's radiation. In case there is life at Jupiter's moon Europa, which has oceans of liquid water underneath its surface covering of ice, scientists don't want Earth bugs to invade this alien world. 

Juno - a mission of many firsts

There are so many reasons to get psyched about Juno. Aside from the exciting scientific data it will beam back at us, Juno is a truly unique spacecraft.

Unlike most probes we sent into the outer Solar System, Juno is not nuclear-powered. Rather, it gets its energy from the Sun with the help of its three huge solar panels. This makes it the farthest solar-powered spacecraft sent by humans.

Because of how far Jupiter is, the amount of sunlight Juno will be receiving is 25 times less than what it would receive here on Earth. To gather as much solar energy, Juno's solar panels were made so big that the whole spacecraft would span a professional basketball court from ring to ring.

Fig 5. Juno is the queen of solar-powered spacecraft. 
Image credit: NASA

Despite the size and efficiency of its solar panels, Juno will only be generating and consuming around 530 watts of power for its scientific instruments. Most household microwave ovens consume more power than this.

To make sure its solar panels always face the Sun, scientists will make Juno orbit around Jupiter in a unique way. Instead of going around Jupiter from west to east like most probes, it will orbit Jupiter from north to south in a very elongated orbit. This will also give the probe a close-up view of Jupiter's intriguing aurorae.

Fig 6. Jupiter's aurora is several times bigger than the whole Earth.
Image credit: X-ray - NASA/CXC/UCL/W. Dunn et al.

Scientists also want to see how Jupiter's internal dynamo produces its colossal magnetic field. The Earth's crust obscures our view of the internal dynamo that produces its magnetic field. Because Jupiter is made of gas, that will not be a problem there. And Jupiter's magnetosphere is truly worthy of study. If humans can see this magnetosphere, it will be comparable in size to a full moon!

Fig 7. If Jupiter's magnetosphere were visible, it would look magnificent when viewed from Earth.
Image credit: NASA Goddard.

To see the countdown of the historic Jupiter Insertion Orbit, view the home page of the Juno Mission at this link: Juno Mission.

*This time is Earth Receive Time, or the time when signals from Juno will arrive here. It will take more than 48 minutes for the light-speed signals to travel from the spacecraft to Earth during JOI.

REFERENCES:

1. National Aeronautics and Space Administration. (2016, July 2). Juno. Retrieved from: https://www.nasa.gov/mission_pages/juno/main/index.html
2. Jet Propulsion Laboratory (2016). Jupiter Orbit Insertion Online Press Kit. Retrieved from: http://www.jpl.nasa.gov/news/press_kits/juno/
3. Wall, M. (2016, July 2). Juno Probe Will Run Hellish Radiation Gauntlet at Jupiter Monday. Space.com. Retrieved from: http://www.space.com/33331-juno-probe-jupiter-radiation-environment.html
4. Ellis, E.G. (2016, July 2). Juno's Jupiter Mission Faces Its Most Critical Moment. Wired. Retrieved from: http://www.wired.com/2016/07/jupiter-can-tell-us-origins-solar-system/

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