Even though several spacecraft have visited Jupiter, and
despite having the best telescopes on Earth and in space, there’s still a lot
we don’t know about the gas giant. We know that 99 percent of the planet is
hydrogen and helium, but the remaining one percent remains a mystery. We’re
also not sure whether there’s a solid core at the center or how Jupiter
generates its powerful magnetic field.
We’ve come up with many possible answers to these questions,
and many of our ideas are well supported by experiments and other space
missions. With the help of Juno, we will make dramatic progress in solving
these mysteries, allowing us to understand how Jupiter formed and became the
planet we know today.
THE SEARCH FOR WATER
One of the biggest questions we have about Jupiter is how
much of it is made of heavy elements – elements that are heavier than hydrogen
and helium. By far the most important heavy element is oxygen, whose most
common form is in water. Oxygen is the third most abundant element in the
universe, and we expect that it should account for more than half of Jupiter’s
heavy-element composition. In fact, the amount of oxygen in Jupiter could weigh
as much as 20 Earths.
PLUNGING INTO JUPITER’S DEPTHS
According to data taken by spacecraft and telescopes,
Jupiter must be made of materials heavier than hydrogen and helium. Most
theories about what Jupiter looks like inside suggest that there’s a solid core
at its center. But so far, we have never been able to verify its existence.
We’re also unsure whether the core is like a solid ball with a surface, or
whether the core’s interface with the rest of the planet is more gradual, with
Jupiter’s interior gas becoming denser until it becomes solid at the center.
Different theories, or models, of how Jupiter formed make
different predictions about the size, mass, and composition of the core. In
some models, Jupiter’s core could weigh as much as three, nine, or even twenty
Earths. By determining what Jupiter’s core is like, Juno will help us narrow
down the correct model. And if Juno finds that the core is nothing like what we
expected, then we would be forced to rethink our ideas about how giant planets
like Jupiter form.
Another mystery is the structure of Jupiter’s swirling
clouds, bands, and storms. Jupiter’s most breathtaking surface features, like
its Great Red Spot, could be connected to the structure and motions of gas deep
in its interior. Or, they could be shallow patterns on the outermost layer of
the atmosphere, like drops of oil on a pool of water. With Juno, we will be
able to see the structure and movement of material deep beneath Jupiter’s
clouds for the first time.
EXPLORING THE MAGNETIC FIELD
Deep inside Jupiter, the crushing weight of the planet
creates extreme temperatures and pressures. Researchers have recreated similar
conditions in the laboratory – but only for mere fractions of a second. Their
experiments suggest that at some point inside Jupiter, maybe about a third to a
half of the way toward its center, the pressure and temperature become so
intense that the planet’s hydrogen gas turns into liquid and conducts
electricity. We think that it’s here, where hydrogen takes on this exotic form,
that Jupiter’s huge magnetic field is produced.
But the conditions here are so strange that we don’t have a
good understanding of what exactly goes on. The magnetic field could be
generated in a way that’s similar to how Earth’s field is generated. Or, the
engine behind Jupiter’s magnetic field could more closely resemble how material
flows inside the Sun. To improve our understanding of Jupiter’s magnetic field,
Juno will map the field and monitor how it changes over time.
As tiny, charged particles fly through space, they get caught
up in Jupiter’s magnetic field, which channels them toward the planet’s north
and south poles. When these particles slam into the poles, they create intense
light shows – Jupiter’s aurorae, northern and southern lights just like on
Earth. Juno is equipped with powerful instruments that can measure the aurorae
and detect these particles as they stream past. These processes also produce
radio signals that Juno can listen to with its radio antennas. The data will
help us understand the complex interactions between Jupiter’s rotation, its
atmosphere and its magnetic field.