What better ways to celebrate Independence Day in the U.S. than family barbecues, splendid fireworks shows . . . and a visit to Jupiter?  That’s right, in addition to the traditional activities, this year’s July 4th holiday will be marked by the arrival of NASA’s Juno spacecraft at the mighty gas giant.

Launched in August 2011, Juno has taken a circuitous route to its destination and will have traveled a little over two billion miles by the time it arrives.  When it gets there, the spacecraft will enter an elliptical polar orbit and is expected to sweep around Jupiter 37 times before the mission’s planned completion, in 2018.

June will follow an elliptical trajectory as it sweeps around Jupiter. (Image credit: NASA/JPL)

Juno's Mission

Astronomers believe that Juno has the potential to make discoveries that will help explain the Solar System as a whole.  Because it is a gas giant revolving around the Sun at a huge distance, Jupiter is essentially invulnerable both to intense solar heat and to asteroids and comets that disappear into its clouds from time to time – forces that have shaped the development of the smaller, rocky planets that are closer to the system’s center.

“Studying Jupiter’s atmosphere is like reading the tree rings of the solar system itself.” – Jeffrey Kluger

Jupiter’s atmospheric chemistry is thought to have been relatively unchanged in 4.5 billion years.  Juno will study that atmosphere down to an altitude of only about 3,100 miles above the clouds, gathering data on the planet’s composition, temperature, structure, its auroras, and other features of interest to researchers.  It will also map Jupiter’s gravitational and magnetic fields, and attempt to determine whether it might have a solid core.

Jupiter is shown tilted on its axis with blue auroras shimmering over its poles. (Image credit: NASA/ESA, The Hubble Heritage Team. Acknowledgement: H. Weaver [JHU/APL] and A. Simon-Miller [NASA/GSFC])

The ambitious agenda of experiments and observations, of course, is dependent on a safe arrival at Jupiter and the ability of the spacecraft to function in the challenging Jovian environment.  The planned polar orbit was chosen to minimize the potential negative impact of the planet’s immensely powerful magnetic field.  Among the precautions NASA has taken is placing the critical flight computer in a titanium-lined vault weighing almost 400 pounds.

Galileo's Earlier Visit

Juno will be the first spacecraft to orbit Jupiter since NASA’s Galileo toured the Jovian system, from 1995 to 2003.  The earlier visitor transmitted important data about the planet’s atmosphere, cloud formations, and magnetosphere, and it also provided images of and fascinating revelations about Jupiter’s largest moons – Io, Ganymede, Callisto, and Europa, which were first identified by the spacecraft’s namesake, Galileo Galilei, in 1610.

Three of Jupiter’s moons leave shadows on the planet. (Image credit: NASA/ESA/Hubble Heritage Team)

Although no one expects Juno to encounter extraterrestrial beings in Jupiter’s neighborhood, it does have some special items onboard.  In tribute to the great astronomer (and to the spacecraft named for him), it carries an Italian Space Agency plaque dedicated to Galileo, along with a figurine of him made of aluminum Lego blocks.

Similarly, the Roman god Jupiter and his goddess wife Juno are represented by two Lego figurines.  Ancient myth tells of jealous Juno pulling back a curtain to witness one of Jupiter’s trysts.  Fittingly, beginning on the 4th of July, spacecraft Juno will peer through a veil of clouds to reveal some of planet Jupiter’s intimate secrets.  Now, those will be sights to see!