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Jupiter, the planet with a solar system of its own – The Planetary Society


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Named after the king of the gods in Roman mythology, Jupiter is a stunning sight to behold. Its red, orange, and yellow swirls, spots, and bands are visible even from small backyard telescopes. Astronomers have observed the planet’s Great Red Spot, a raging storm larger than Earth, for at least 200 years.
Jupiter was the first planet in our solar system to form. It was probably born much closer to the Sun before migrating to its current position about 4 billion years ago, scattering asteroids and comets with its gravity in the process. Some of those asteroids and comets slammed into early Earth, possibly bringing water here in the process — the key ingredient for life as we know it.
Many exoplanets — planets in other solar systems — we have discovered are Jupiter-like worlds close to their stars, reinforcing the idea that our own solar system’s large planets have moved from their original positions. By studying Jupiter and comparing it to similar exoplanets, we learn how solar systems evolve and the possibilities for life elsewhere.
Jupiter has a faint ring system and at least 79 moons, four of which are active, planet-like worlds ranging in size from just smaller than Earth’s Moon to larger than Mercury. All but Io likely have liquid-water oceans under their surfaces, making them possible havens for life. Europa’s ocean in particular may be the most biologically promising environment beyond Earth for life. Jupiter challenges our perceptions about where life can exist in the universe.
Meet the Moons
Jupiter and its moons are essentially a miniature solar system unto themselves and can together teach us a lot. Every branch of planetary science has questions that can be answered here: atmospheric scientists can study storm dynamics on Jupiter, geologists can examine diverse terrains on moons with active volcanoes and geysers, and astrobiologists can search for life.
Average temperature: -108°C (-162°F) where atmospheric pressure equals sea level on Earth
Average distance from Sun: 779 million kilometers (484 million miles), or 5.2 times farther from the Sun than Earth
Diameter: 142,984 kilometers (88,846 miles), Jupiter is 11.2 times wider than Earth
Volume: 1,431 trillion km3 (343 trillion mi3), Earth could fit inside Jupiter 1,431 times
Gravity: 23.1 m/s², or 2.4 times that of Earth’s
Solar day: 10 Earth hours
Solar year: 4,333 Earth days
Atmosphere: 90% hydrogen, 10% helium, less than 1% other gases
Jupiter has long been studied from Earth-based telescopes. Galileo Galilei’s observations of Jupiter’s moons in the early 1600s revolutionized humanity’s understanding of the universe by showing that not every celestial object orbits the Earth, which was the leading theory at the time.
NASA’s Pioneer 10 spacecraft made the first Jupiter flyby in 1973, returning the first close-up images of Jupiter and discovering the planet’s huge magnetic field that traps charged particles from the Sun, creating a deadly radiation field. Spacecraft exploring Jupiter must carry radiation shielding to survive.
NASA’s legendary Voyager 1 and 2 spacecraft flew past Jupiter in 1979, capturing up-close views of the Galilean moons that revealed they were complex worlds unto themselves, with volcanoes, oceans, and other significant features. The probes also saw Jupiter’s faint ring system. The planet finally received its own, dedicated mission when NASA’s Galileo spacecraft arrived in 1995 and orbited Jupiter until 2003. Galileo dropped a probe into Jupiter’s atmosphere to measure its composition and discovered evidence of Europa’s saltwater ocean.
What’s under Jupiter’s beautiful clouds? When Jupiter formed, it likely had a large, rock-and-metal core. But as the planet gobbled up leftover gases from the solar system’s formation, intense pressures may have dissolved the core into an exotic substance called metallic hydrogen. The most recent data from NASA’s Juno spacecraft suggests there is no distinct core.
Though Jupiter’s immense gravitational field wreaked havoc during the solar system’s early days, today it shepherds the orbits of asteroids and helps protect the inner solar system. Comet Shoemaker-Levy 9 impacted Jupiter in 1994, just as the Galileo spacecraft was approaching the planet. Galileo teamed up with Earth-based telescopes to watch the impact, and the observations taught us valuable lessons about the importance of defending our own planet from asteroids and comets.
In 2016, NASA’s Juno spacecraft entered orbit around Jupiter to find out what’s at the giant planet’s core, map its magnetic field, and measure how much water and ammonia are present in the deeper levels of its atmosphere. These measurements are helping us learn more about Jupiter’s formation and evolution.
The European Space Agency’s JUICE (JUpiter ICy moons Explorer) mission will launch in 2022 to explore Jupiter’s Galilean moons. JUICE will orbit Ganymede in the late-2020s after flybys of Europa and Callisto, aiming to figure out whether the moons’ subsurface oceans could support life. NASA’s Europa Clipper mission will launch in the mid-2020s to try and answer the same question at Europa by performing a detailed survey of the moon.
Space missions to worlds like Jupiter don’t just happen, they require persistent, organized support from both scientists and the public alike. In the U.S., the scientific community has a formal process to set NASA’s exploration priorities called the decadal survey. This once-a-decade effort represents a consensus opinion of top scientific goals in the solar system, and, once released, requires support from the public and organizations like The Planetary Society to ensure those priorities are funded. Europa Clipper was a top recommendation of a prior decadal survey, yet required years of steady advocacy to become reality.

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