Frequently Asked Questions

About Juno Mission

About Jupiter

FAQ Answers

1. Why is the mission called Juno?

Painting of Jupiter and Io by Correggio

Painting of Jupiter and Io by Correggio (Kunsthis-
torisches Museum, Vienna)

Juno, the god-sister-wife of Jupiter, maintained a constant, jealous vigil over her god-husband's dalliances from Mount Olympus. When Jupiter had his tryst with Io, he spread a veil of clouds around the entire planet to conceal his activities. Upon observing the cloud-cloaked planet, Juno immediately suspected Jupiter of concealing activities that would not bear the light.

Hence, Juno came down from Mount Olympus and employed her special powers to penetrate the clouds and reveal the true nature of Jupiter.

Listen to Dr. Bolton (Juno Mission Principal Investigator) explain the choice of the name of the mission.

2. How important for an understanding of the solar system do you believe the Juno mission to be ?

To understand how the solar system formed we need to understand how much oxygen (most commonly found as water) there is inside Jupiter. Did Jupiter collapse from the original cloud of gas? Or, did Jupiter form by the gravitational attraction of hydrogen gas onto a core of ice and rock? Or, was more ice added later when large, left-over ice balls collided with Jupiter? These different ideas all predict different amounts of water in the outer layers of Jupiter. Unfortunately, scientists have been unable to measure the amount of water at Jupiter.

Dr. Fran Bagenal

Answered by: Juno Co-Investigator Dr. Fran Bagenal, Professor of Astrophysical and Planetary Sciences at the University of Colorado, Boulder, Colorado, USA

3. How do scientists plan to use the information gathered about Jupiter to understand water on Earth ?

Current ideas about the formation of the solar system suggest that the Earth formed at about its present distance from the Sun where it was too warm for ice to condense. This means that we think that Earth formed from balls of rock and metal that condensed out of the original cloud of gas close to the Sun. This means that the water was delivered to the Earth later - after the planet was formed. One possible source of water for the Earth is a population of large ice balls that condensed out beyond the "frost line" (probably beyond the asteroid belt) - ice balls left over from the formation of the cores of Jupiter and the other giant planets. Being the largest, most-massive planet in the solar system, Jupiter is thought to have stirred up the left-over ice balls and sent them hurtling to the Earth. Some of these ice balls may have been responsible for the large craters on the Moon. The early phases of the solar system was a dangerous time!

Dr. Fran Bagenal

Answered by: Juno Co-Investigator Dr. Fran Bagenal, Professor of Astrophysical and Planetary Sciences at the University of Colorado, Boulder, Colorado, USA

4. Can you please describe the orbit paths of the Galilean satellites ?

The 4 Galilean satellites - Io, Europa, Ganymede and Callisto (in order away from Jupiter) - all have very circular orbits that lay very close to the equatorial plane of Jupiter. The inner 3 have very special orbits - these moons are in a orbital resonance. This means that for every once that Ganymede orbits Jupiter, Europa orbits almost exactly twice and Io almost exactly 4 times.

Here is a little movie of these motions.

Dr. Fran Bagenal

Answered by: Juno Co-Investigator Dr. Fran Bagenal, Professor of Astrophysical and Planetary Sciences at the University of Colorado, Boulder, Colorado, USA

5. What one aspect of Jupiter interests you most and why ?

I am particularly interested in Jupiter's strong magnetic field and the charged particles that are trapped by the planet's magnetic field - similar to the Van Allen belts around the Earth (discovered 50 years ago by the first US rocket into space)!

Dr. Fran Bagenal

Answered by: Juno Co-Investigator Dr. Fran Bagenal, Professor of Astrophysical and Planetary Sciences at the University of Colorado, Boulder, Colorado, USA

6. Could you tell me about Jupiter's unique composition ?

Actually, the problem is that we really do not know Jupiter's chemical composition. In particular, we would think that Jupiter should have about the same composition of the Sun - after all, they both came from the same large cloud of gas. But Jupiter seems to have higher amounts of elements heavier than hydrogen and helium. In particular, we do not know the amount of oxygen - the third most abundant element in the universe after hydrogen and helium. That's why Juno is designed to measure the amount of water at Jupiter... more about that later.

Dr. Fran Bagenal

Answered by: Juno Co-Investigator Dr. Fran Bagenal, Professor of Astrophysical and Planetary Sciences at the University of Colorado, Boulder, Colorado, USA