Jupiter! The largest planet in our solar system, a bulging beauty known for its ominous Great Red Spot. It's also a world cloaked in mystery, full of puzzles that scientists are working to solve.
NASA's Juno spacecraft is scheduled to arrive at the giant planet on Monday (July 4), to do more investigations of this giant planet and to try to solve some of the following mysteries.
Scott Bolton, principal investigator of Juno at the Southwest Research Institute in Texas, told Space.com what some of the biggest outstanding questions are. [Closing in on Jupiter: 7 Fun Facts About Juno's Mission]
1. How did Jupiter get enriched in heavy elements, compared with the sun?
Jupiter is 317 times more massive than the Earth, making it a real heavyweight in the solar system. It is believed that the planets in the solar system formed from the same hydrogen-helium cloud from which the sun was created. But here's the catch: The Galileo probe, which looked at Jupiter in the 1990s and 2000s, found a different abundance of heavy elements in Jupiter than in the sun.
One theory (proposed at the time by Galileo scientists) is that Jupiter's heavy elements come from the numerous comets, asteroids and other small bodies that it has pulled in and "consumed" when they get too close. But scientists aren't quite sure. One of Juno's aims will be to measure these elements at higher precision than previous missions.
2. What is the global abundance of water in Jupiter?
Water is key to understanding how Jupiter was formed. According to NASA, water ice (likely in the form of comets or asteroids sucked into the giant planet) brought heavier elements to Jupiter besides the original hydrogen and helium floating around in the solar system.
"Knowing the water abundance will tell us the original form of that ice and hence help define the conditions and processes in the original cloud of dust and gas that led to the origin of Jupiter," according to the Juno mission page. "Those same conditions and processes were forming other planets, too. Because this enormous planet contains most of the water in the solar system, we can expect this investigation to help us understand the origin of the life-giving water on Earth."
A surprising recent finding is just how persistent water can be after a comet crashes into Jupiter. A famous comet called Shoemaker-Levy 9 broke up into pieces before peppering the planet in July 1994. About 20 years later, the Herschel Space Observatory detected an abundance of water in Jupiter's stratosphere that came from Shoemaker-Levy 9 (which was clear because most of the water vapor was around the impact sites).
3. Does Jupiter have a core of heavy elements at its center?
The physics of Jupiter are hard for even space scientists to imagine. Jupiter is made up of 90 percent hydrogen, which exists in the outer layers as gas (just like on Earth). Deeper inside the planet, however, the hydrogen is under so much pressure that the electrons are squeezed out, creating a fluid that conducts electricity like a metal, according to a 2011 NASA feature story.
This creates a huge magnetic field within the planet, which is also strengthened by Jupiter's rapid rotation. Auroras shine brighter on Jupiter than anywhere else in the solar system. At the core of Jupiter, however, the composition is anyone's guess. No one is sure how far the liquid hydrogen layer penetrates and if the core has heavier elements inside. Juno aims to figure out more about Jupiter's insides by examining the planet's atmosphere, gravity and magnetic field.
4. How deep do the zones, belts and storm features, such as the Red Spot, go?
Images of Jupiter show thick stripes and swirling storms, but most of these pictures capture only the tops of the clouds that cover the giant planet. It's unclear what the weather is like deeper down, inside Jupiter, and whether the features that can be seen on the surface are present below.
"Juno will determine the global structure and motions of the planet's atmosphere below the cloud tops for the first time, mapping variations in the atmosphere's composition, temperature, clouds and patterns of movement down to unprecedented depths,” NASA wrote on the Juno website.
Understanding the long-term weather on Jupiter will also help scientists solve mysteries such as why its Great Red Spot is shrinking. This storm feature has been known to astronomers ever since telescopes were first available in the early 1600s. But since 1930, astronomers have noticed the storm getting smaller and smaller; in 2014 it was at its smallest stature ever. Once estimated as large enough to fit three Earths across its width, the storm is now no bigger than Earth's diameter.
5. How does the interior of Jupiter rotate?
When you look at the exterior of Jupiter, you can see that the zones and bands don't move in concert with each other. There are changes in their rotation and sizes from night to night, changes that are even apparent in amateur telescopes.
Deeper down in Jupiter's atmosphere, what is happening is even less understood. To date, planetary probes have mostly been looking at the surface of the giant planet. Juno aims to probe a little deeper to see how the interior of Jupiter rotates.
6. How and where does the magnetic field originate?
The magnetic fields found around planets like Earth are thought to be caused by the flow of liquids within the core (in the case of Earth, the fluid is iron). Things are more complicated on Jupiter, however. As mentioned earlier, the planet has liquid hydrogen closer to its center that would also conduct, much like a metal. So it is unclear if the magnetic field originates from there or from deeper within the planet, or if the field is created through some sort of dual process.
Figuring out what is happening in Jupiter could not only help us understand magnetism in giant planets in our own solar system, but could also help scientists make predictions about planets outside the solar system. Jupiter is considered a model for exoplanet studies, although there are very weird Jupiter-size planets out there. For example, some orbit very close to their parent stars. [What’s Inside Jupiter? Close Encounters With The Giant (Video)]
7. What drives the aurora in Jupiter?
Jupiter's auroras were first spotted when the Voyager 1 spacecraft flew by in 1979. When astronomers later turned X-ray telescopes toward the planet, however, they saw much more power than anticipated. Auroras are so frequent on Jupiter, in fact, that in a 2007 news release astronomers said they see the auroras every time they look at the giant planet.
The process for generating these fields, however, is poorly understood, NASA added in the same release. Scientists know that Jupiter has enough spin to produce its own auroras (unlike the Earth, which relies fully on solar activity). They also know the auroras come from charged particles, mainly (in Jupiter's case) from volcanic plumes on the moon Io. But it's unclear how the particles make their way from Io to Jupiter's magnetosphere. Closer study will be required by the Juno spacecraft.