The Juno probe itself is packed with scientific wizardry. Including its massive solar panels, it is roughly the size of a basketball court and includes advanced sensors to probe the interior of Jupiter. The Juno mission should also reveal more details of the planet itself than its predecessor, the Galileo mission
(which arrived at Jupiter in 1995).
That earlier mission was historic: Galileo was the first spacecraft to orbit and then take detailed picture of Jupiter and its moons, although it suffered from a partially disabled antenna. It took spectacular pictures of the moons of Jupiter, even revealing the possible presence of an ocean under the ice cover of its moon, Europa. However, it did not give scientists as much insight as they hoped into the nature of the planet itself.
As a result, Jupiter itself
still remains much of a mystery, although it is the 800-pound gorilla that dominates the solar system. It is so massive that
if it were hollow, you could place over 1,300 Earth-like planets inside it. Because it is heavier than all the other planets combined, its presence determines the past and future of the solar system.
For reasons still not understood, it is surrounded by a ferocious radiation belt that is so powerful it can cripple a spacecraft. In fact, the radiation field is so intense that it creates much of the static you hear on a radio. (So you can blame Jupiter the next time you hear static when listening to the radio.)
Jupiter also makes life on Earth possible. Its gravity field is so huge, it acts like a gigantic vacuum cleaner, sucking in comets, asteroids, and cosmic debris in the solar system. What it cannot absorb, it can also fling into outer space. Without Jupiter cleaning out the early solar system, the Earth would be pock-marked with meteor collisions. We would suffer from asteroid impacts every day. CNN studios would probably be a gigantic crater it if wasn't for Jupiter. (Today, astronomers, when they try to simulate the creation of new solar systems in outer space capable of harboring life, have to include the presence of a Jupiter-sized planet to clean out the debris.)
But, though our very life depends on Jupiter, we know very little about the planet itself. Early astronomers, for example, first discovered the gigantic red spot on Jupiter. It is probably the largest hurricane in the solar system, so big that it can easily swallow up Earth, but little is known about where it came from or its energy source.
Also, little is known about the interior of the planet. Beneath its cloud cover, scientists suspect there is a vast ocean of liquid hydrogen. (When the Galileo mission was deorbited, it was deliberately crashed into Jupiter on September 21, 2003, and probably sank in this liquid hydrogen ocean.) Nothing is known, however, about what lies beneath this ocean. Most likely, it is some form of metallic, solid hydrogen, with perhaps a rocky core at the very center, a remnant of the birth of the planet itself. However, all this is speculation.
The very existence of Jupiter, and hence the planets of the solar system, is also a tremendous mystery. The Kepler space probe and astronomers, using telescopes on Earth, have identified on the order of 2,000 planets orbiting other star systems, most of them resembling Jupiter. But the mystery is: Why is our Jupiter so exceptional in the universe?
Most Jupiter-sized planets orbit the mother star in a highly elliptical orbit. This means they will often cross the orbit of any Earth-like planet and fling it into outer space, making life impossible. But our Jupiter travels in a near-perfect circular orbit, preventing a collision with any Earth-like planet, making life possible.
Furthermore, many Jupiter-sized planets in other solar systems travel around their mother star in a very small orbit (sometimes comparable to roughly the orbit of Mercury, the nearest planet to the sun). But in the 1980s, astronomers universally believed that all Jupiter-sized planets originated in deep space, far from the mother star.
The discovery of these new Jupiter-sized planets that orbit close to their sun forced astronomers to contemplate a once heretical idea: that Jupiter-sized planets originate far from the mother sun, like our Jupiter, but then somehow migrate and spiral into the inner solar system. In the process, these migrating Jupiter-sized planets would again cross the orbit of any Earth-like planet, and destroy it. So why is our Jupiter so different from the other Jupiters in space, in that it doesn't migrate?
Like the Galileo mission before it, the Juno probe will end its life by plunging into Jupiter. This will happen after circulating around Jupiter 37 times over 20 months. But before its final hurrah, it will have given us fresh insight into the nature of the solar system, its birth, its evolution, and its future. It will help us to understand the birth of the solar system, and why we exist at all.