Artist rendering of Juno spacecraft in orbit around Jupiter. NASA

The last NASA mission to orbit Jupiter, the Galileo, was designed, flown and its data analyzed as if it was circling the only Jupiter in the sky.

This is hardly surprising since the spacecraft launched in 1989, before the exoplanet era had arrived.  Ironically, Galileo entered its Jupiter orbit in late 1995,  just a few months after the first exoplanet was detected.

That planet, 51 Pegasi b, was a Jupiter-sized planet shockingly close to its host star, and its location and white-hot temperatures turned upside down many then-current theories about gas giant planets and their roles in the formation of solar system.  Scientists are still struggling to make sense of what 51 Pegasi b, and the 250 or so Jupiters found after it, are telling us.

So the Juno mission, which is scheduled to begin orbiting Jupiter on July 4, will arrive at a planet understood quite differently than when Galileo made its appearance.  Juno was built first and foremost to unravel some of the enduring mysteries of the planet:  When and where was it formed?  Does it have rocky core?  Is there water deep in the atmosphere?

But the spacecraft and its instruments will do their unraveling within our current, very different galactic context, where exoplanet scientists will be waiting for results with nearly as much eagerness and anticipation as solar system and planetary scientists.  And the findings from Juno may well have as much impact on the subsequent study of the many, many Jupiter-like planets known to exist in other solar systems as it does on the study of our solar system and its formation history.

Scott Bolton, principal investigator for Juno, recently told a NASA gathering that one of the primarily goals of Juno is to learn, through exploration of Jupiter, “the recipe” for the formation of our planets, our solar system, and those solar systems and planets well beyond Earth.

This is possible because Jupiter was the first planet formed after our sun, which is made almost entirely of hydrogen and helium.  Jupiter is also largely made up of those two elements, but it does have some additional heavy elements that somehow got there — carbon, nitrogen, phosphorus, important gases.

“We don’t know exactly how that happened, but we know that it’s really important,” Bolton said.  “That’s because the stuff that Jupiter has more of is what we’re all made of made of, and is what Earth is made out of, and what life comes from. … Read more