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Jupiter and Its Moons, an Exploration History

I love researching planetary science and tracking NASA's latest efforts to explore the universe.

Jupiter: The Gas Giant

Jupiter is by far the largest planet in the solar system spanning 86,000 miles in diameter. It is bright enough to easily be seen from Earth, no wonder the Romans named it after their god of thunder and storms. The planet is made up of gaseous hydrogen and helium with a turbulent atmosphere so there are actually many large and violent storms down at the surface.

Learn more about the planet, its moons and humanity's efforts to learn more about them.

Image of Jupiter, 5th planet from the Sun, from the Hubble telescope.

Image of Jupiter, 5th planet from the Sun, from the Hubble telescope.

Jupiter's Exploration History

Various spacecrafts have gathered information about Jupiter and its composition during flybys, like Pioneer and Voyager. Until recently, NASA's Galileo (launched in 1989) was the only spacecraft to perform a long duration mission around Jupiter. It orbited the gas giant and sent an atmospheric probe to report data back to scientists on Earth. The mission was able to gather information on the composition of Jupiter's four large satellites, study storms on the surface of the planet and examine the dust rings around it.

Perhaps Galileo's most significant discovery was the possibility of a very large ocean on the surface of one of Jupiter's moons, Europa. The presence of water has led to speculation as to whether the moon could have supported life.

Galileo's mission was completed in 2003 when it was commanded to crash into Jupiter's surface once it no longer had the resources to stay operational, a typical end to the service life of an orbiter.

Besides Galileo, a few other missions flew close to Jupiter in what the space exploration community calls "flybys". Flybys can provide information through images and sensors without committing the craft to an orbit.

First Image from Jupiter's New Satellite: Juno

First image returned to Earth from Juno. Three of the four moons are shown.

First image returned to Earth from Juno. Three of the four moons are shown.

NASA's Juno Mission to Jupiter

Juno Mission (2011-2018)

NASA launched Juno (built by Lockheed Martin) in 2011 to begin a five year journey to cross the 588 million kilometers from Earth to Jupiter. The Juno spacecraft is powered by three large solar arrays and is the first solar powered vehicle operated by NASA to travel that far from Earth.

Juno's trajectory let it steer clear of Jupiter's heavier radiation regions, the deadliest in the solar system. It propelled itself over the radiation regions in plane with the planet and settled into orbit and then will leave the orbit by flying out below the planet. It carries scientific instruments to take measurements of the planet as well as a color camera called the JunoCam to send pictures back to Earth.

Juno's main goals are to provide scientists data on Jupiter's gravity and magnetic field as well as analyze the water content in Jupiter's atmosphere. All of this information will allow scientists to better understand how gas giants are formed and how they are able to stay relatively stable, something scientists have not been able to explain.


Europa compared to planet Earth and its moon

Europa compared to planet Earth and its moon

Jupiter's Moons

Jupiter has many satellites but the most well known are the four largest: Europa, Io, Ganymede and Callisto. They were first discovered by Galileo (that was Galileo Galilei in 1610, not the 1989 mission named after him) and thus called the Galilean moons. Mostly due to their old age and Jupiter's strong gravitational pull these four moons are very unique and intriguing to scientists.

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  1. Ganymede, at 3,273 miles in diameter, is the largest satellite in the solar system, right behind Saturn's Titan. It is large enough to have its own magnetic field.
  2. Callisto is Jupiter's second largest moon. It has a lower density than the other large moons and unlike the other three has very little geographic activity.
  3. Io is the driest object is the solar system and thought to the most geologically active. Sulfur and sulfur dioxide make up most of the surface with regular lava flows from its hundreds of active volcanoes.
  4. Europa is the smallest of the Galilean moons and many consider it to be the most significant to science. Many of the satellite's characteristics such as its oxygen atmosphere and the possibility of liquid water beneath its ice crust lead some scientists to theorize that it could have at one time supported extraterrestrial life.

Ganymede, Io and Europa are in a unique 1:2:4 orbital resonance around Jupiter, which means they periodically affect each other with their gravity. This causes the stretching of the satellites that is responsible for the friction that causes their tidal heating and geological activity.

All four Galilean moons are named after one of Zeus's many lovers. Jupiter was the Roman equivalent of the Greek god of thunder Zeus. You can see why NASA engineers named the probe they sent to investigate the moons after Jupiter's wife, Juno.

Jupiter Facts Quiz: Are you a Jupiter Expert?

For each question, choose the best answer. The answer key is below.

  1. How many Galilean moons are in orbit around Jupiter?
    • 2
    • 4
    • 3
    • Jupiter doesn't have any moons.
  2. In Roman mythology, who are Jupiter and Juno?
    • Jupiter is the god of war, Juno is the goddess of peace.
    • Jupiter is the god of the sun, Juno is the goddess of the stars.
    • Jupiter is the god of sky and thunder, Juno is his wife.
  3. How far away is Jupiter from Earth?
    • 176 million kilometers
    • 2 billion kilometers
    • 588 million kilometers

Answer Key

  1. 4
  2. Jupiter is the god of sky and thunder, Juno is his wife.
  3. 588 million kilometers

Interpreting Your Score

If you got 0 correct answers: Oops. Read on to learn more about what we know about Jupiter.

If you got 1 correct answer: Oops. Read on to learn more about what we know about Jupiter.

If you got 2 correct answers: You can do better than on to learn more about what we know about Jupiter.

If you got 3 correct answers: Great job!


Katy Medium (author) from Denver, CO on September 05, 2016:

Great to see some Jupiter fans! You inspired me to put some Juno updates to this Hub on my to do list. First, more recent images and eventually the results from what NASA analysts found.

Readmikenow on September 05, 2016:

Excellent Hub. I understand the Russians also had a successful mission to Jupiter and were able to obtain some good photographs. It was a few decades ago when it happened. Enjoyed reading it.

CJ Kelly from the PNW on September 04, 2016:

Great job. Can't enough Jupiter. Sharing everywhere.

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