Editor’s note: Beneath Jupiter’s clouds

The ancient Romans named the planet Jupiter after the king of the gods, who sometimes hid himself behind a veil of clouds through which only his wife, Juno, could see. Though the Romans could not have known it, the planet too is concealed beneath clouds that scud and swirl across the top of its atmosphere.

When NASA decided to send a spacecraft to peer through the veil and “reveal Jupiter’s true nature”, only one name would do: Juno. 

The Juno probe was launched in 2011. After a five-year voyage it settled into orbit around Jupiter two years ago. It is now at the end of its scheduled mission. So what has it uncovered? 

Juno has certainly been busy beaming home bursts of photos each time the probe’s orbit brings it close to Jupiter. The pictures have captured the public imagination and redrawn our understanding of the solar system’s largest planet. 

These dazzling images have revealed a new world of detail in the intricate, filigreed patterns of the Great Red Spot and the chaotic fringes of Jupiter’s striped atmospheric bands, as well as delivering our first look at the polar regions with their arrays of interlocking cyclones and storms.

Despite their breathtaking beauty, these photos are only a side note – taken with a wide-angle camera added to Juno almost as an afterthought – to the main mission. Juno’s principal scientific purpose is to peer beyond Jupiter’s cloud tops with microwave sensors and other instruments.

Take the Great Red Spot: this enormous storm has a circumference bigger than the Earth. Astronomers have watched it for centuries. But no one has ever been able to tell how deep it goes. Is it a superficial swirl on the skin of the atmosphere, or a deep vortex that extends far into the planet’s interior?

By looking through Juno’s eyes, scientists have been able to see infrared radiation emitted from far below the surface, revealing that the storm goes down at least 350 km below what can be seen with the naked eye. {%recommended 7386%}

In this issue of Cosmos, we celebrate the Juno mission with a look at what it has revealed about Jupiter. As Richard A. Lovett writes, “it’s already proven well worth its $US1.1 billion price tag.”

Everything Juno has seen and done has provided valuable information. By studying minute fluctuations in the speed of the probe, scientists have measured small variations in the planet’s gravity field. These variations in turn have revealed that

Jupiter’s atmospheric bands, the different-coloured stripes of wind moving in opposite directions that mark the surface so clearly, extend thousands of kilometres into the interior, where gravitational pressure squeezes the atmospheric gases into liquid. 

These could be just the beginning of Juno’s discoveries! As Cosmos goes to press the probe is just weeks away from the end of its scheduled life. Will its next close orbit end, as Cassini’s did, with a death dive to protect moons from contamination? Jupiter’s moon Europa has water and maybe life. 

Or will the mission be extended? We here at Cosmos certainly hope Juno’s unveiling of Jupiter will continue.