The spacecraft will focus on exploring the inner workings of Jupiter. "We're sending Juno out there to try to understand the origin and evolution of Jupiter, ... to explain how much water there is, what it's like inside, what the atmosphere is like," Fran Bagenela of the University of Colorado told a group of scientists at the recent meeting of the American Astronomical Society in Anchorage, Alaska.
Probing Jupiter's interior was first attempted in 1995 when NASA's Galileo atmospheric probe was the first man-made object ever to plunge into Jupiter's roiling atmosphere. The spacecraft was presumably crushed when atmospheric pressure rose to over 23-times Earth's surface pressure and temperatures passed 300 degrees Fahrenheit (150 degrees Celsius).
Looking at the telemetry sent back by Galileo, scientists were surprised to find much less water than expected deep in Jupiter's atmosphere. After all, Jupiter is theorized to have bulked up to its size in the icy region of the circumstellar disk of gas and volatile materials that encircled the newborn sun 4.5 billion years ago.
Bagenela believes that the Galileo probe fell at the boundary between one of the brown atmospheric zones and white belts that form a striped pattern across the giant's face. This gap region could have been unusually dry. It's as if space aliens sent a probe to Earth and it descended over Denver during a Chinook where dry winds descend from the Rocky Mountains, says Bagenela.
Juno's microwave instruments should detect water deep in Jupiter's interior. Water absorbs microwaves from Jupiter's heat, just as water behaves in a microwave oven. A straightforward measurement of the strength of the microwaves radiating from Jupiter will give a tally of the water supply. This will also tell how much oxygen is locked inside Jupiter.
Jupiter is prototypical of gas giant planets found elsewhere in our Milky Way galaxy, but the only world where we can get details of its composition and inner workings. Though Jupiter-sized worlds are not thought to be abodes for life - at least not life as we can imagine it - they could host one or more inhabitable moons.
However such moons would have to lie far outside a gas giant's immense magnetic field, assuming Jupiter is a true archetype of such worlds. Jupiter is largely a ball of whirling metallic hydrogen - a form of hydrogen not found on Earth - that drives the dynamic electron flow. The magnetic field is 100 times stronger than Earth's.
HOWSTUFFWORKS: Jupiter Explained
Like threading through the eye of a needle, the 66-foot diameter probe will skirt the edge of Jupiter's radiation belts and plunge down toward the poles. It may survive 33 orbits before radiation - intense enough to kill a human in a few minutes - fries its electronics, which are encased in a vault of titanium. It's doubtful even Superman could survive this task.
Juno's ultimate fate is to be deorbited into Jupiter's atmosphere, like its Galileo predecessor. This is to avoid potentially biologically contaminating any of Jupiter's moons in a wayward collision with the Earth visitor.
Image credit: NASA, Lunar and Planetary Insitute