Juno set to answer big questions at Jupiter

Almost five years after it was launched, NASA’s Juno spacecraft will arrive at Jupiter on July 4, and Ron Hobbs is pretty excited about it. Hobbs, a Seattle-based NASA Solar System Ambassador, recently learned the inside scoop about the Juno mission during a teleconference with the mission’s principal investigator, Dr. Scott Bolton, who is the associate vice president for the space science and engineering division at the Southwest Research Institute.

Juno at Jupiter

Artist concept of Juno at Jupiter. Image: NASA/JPL.

“The Juno mission is about reverse-engineering the recipe of the soup that is our solar system,” Hobbs said. He noted that the Sun contains the vast majority of the mass in the solar system. After the Sun was born, Jupiter formed next, and it weighs two-and-a-half times more than everything else—the rest of the planets, comets, asteroids, the works.

Juno has four main scientific objectives, according to Hobbs: figuring out what’s at Jupiter’s core, studying the planet’s atmosphere and magnetosphere, and figuring out where its water came from.


Ron Hobbs

NASA/JPL Solar System Ambassador Ron Hobbs. Photo: Greg Scheiderer.

“The present theories about the solar system origin and evolution do not explain how Jupiter was enriched in heavy elements,” Hobbs said, noting that, in astronomical terms, anything above hydrogen or helium is considered heavy. “The key to understanding how the giant planets form, and then how the rest of the planets form, and how other planetary systems form is really the key to how those heavy elements got into Jupiter.”

Hobbs noted that the Galileo mission in 1995 sent a probe into Jupiter in search of water but didn’t find much. Scientists speculate they may have just gotten unlucky, and hit a sort of Sahara Desert area of Jupiter. Juno will avoid that problem by using antennas to measure microwave radiation from Jupiter; we’ll be able to tell how much water is there by how much energy is absorbed. It’s a lot less costly than probes and we’ll be able to get measurements from all over Jupiter and to greater depths.


Juno will answer questions about Jupiter’s most visible features as it studies the Jovian atmosphere.

“It’s going to be able to get atmospheric composition, temperature, cloud opacity and dynamics to depths greater than 100 bars at all latitudes,” Hobbs said. “We’re really going to start to understand what those belts and zones that we see here from Earth are composed of.”


“Jupiter has a huge magnetosphere, and there’s still some uncertainty about how it formed,” Hobbs noted. Like Earth’s Van Allen Belts, there’s a lot of radiation trapped there.

“They’re so intense at Jupiter that any spacecraft going into them is in danger of having its electronics fried,” Hobbs said. “Humans, living things, would never survive; the radiation levels are just incredible.”

Juno will make polar orbits around Jupiter. Previous missions have taken equatorial orbits. Hobbs said the polar orbit will help the craft avoid intense radiation, and will create some great imaging opportunities.

“We know that Jupiter has incredible aurorae, but they’ve never been seen up close,” Hobbs said. “In polar orbit Juno is going to be able to get close-up views.”

Gravity science

Jupiter is known as a “gas giant,” but scientists believe it has a metallic core of really heavy elements: iron, nickel, silicon and the like. They don’t know for sure.

“The gravity science that Juno will do will answer that question, will tell us the interior structure,” Hobbs explained.

Juno will study the interior of Jupiter by mapping both its gravitational and magnetic fields. Hobbs said scientists expect to find metallic hydrogen.

“We believe that at some point down in this giant body hydrogen is under so much pressure that it becomes a metal,” Hobbs said. “We believe there’s a whole ocean, if you will, or mantle of metallic hydrogen.”

About Juno

Hobbs said Juno is the second mission of NASA’s New Frontiers program. New Horizons, which flew past Pluto last summer, was the first.

“New Frontiers is a follow-on to the Discovery program, where NASA basically funds investigator-led missions,” Hobbs said. “The Discovery missions are all low-cost missions, largely to the inner solar system, but there were enough targets of opportunity that they saw the need for an expanded program.”

Juno will make 33 orbits of Jupiter, each taking about two weeks. It will get within 5,000 kilometers of its cloud tops. The electronics are protected from radiation inside a 200-kilogram titanium vault. The craft is powered by huge solar panels that are about 80 feet across as the craft spins. It will be the furthest we’ve sent a solar-powered spacecraft.

Juno Cam

Junocam photo of Earth

This image of Earth was taken during the close flyby of NASA’s Juno spacecraft on October 9, 2013. The coastline of Argentina is at the upper left, and clouds cover much of Antarctica at bottom. Image credit: NASA/JPL-Caltech/MSSS

Juno will be spinning, which makes photography a challenge. But we love our space images, and Hobbs said the craft carries the Juno Cam to grab photographs, though it’s not considered to be an official scientific instrument. Still, it took some great images of Earth during a gravity-assist fly-by in 2013. Hobbs said Juno Cam is naturally outside the titanium vault, which will leave it exposed to radiation.

“I’m looking forward to getting those pictures taken and down here on Earth early on in the mission, because I have a feeling it’s going to be one of the first things that gets fried,” he said.

Hobbs is looking forward to getting data from Juno starting next month.

“It’s a cool mission and it’s answering some really fundamental questions,” he said. “We’re going to learn a lot about our place in the universe once again.”

Podcast of our conversation with Ron Hobbs: