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Juno - Unlocking the Mysteries of Jupiter and the Solar System


The excitement that Paul Steffes felt five years ago as he watched Juno lift off into the Florida sky is nothing compared to the feelings he has these days.

“It really is amazing,” Steffes said recently.

Steffes, a professor in Georgia Tech’s School of Electrical and Computer Engineering, is a member of the Juno Science Team, giving him first access to data beamed to Earth from Jupiter. The basketball court-sized spacecraft is currently circling the gaseous giant after finding its orbit on the evening of July 4. The mission is designed to improve our understanding of the birth of the solar system and the mysteries of its largest planet.

“We’ve already been surprised countless times, and Juno has only circled Jupiter a few times,” he said. “It’s different from what we expected.”

Steffes and the remainder of the team are purposely being coy when publicly discussing the early data. They want to be sure their findings are correct, then they will submit them to a scientific journal for review.

“We’re learning so much, and we can’t wait to share the news soon.”

NASA photo of JUNO in clean room with scientists.

Juno’s six microwave detectors will provide data on the structure, movement, and chemical composition of Jupiter’s atmosphere up to 342 miles below the visible cloud tops. The largest of MWR antenna, above, takes up a full side of the spacecraft. Image source: NASA/JPL

Officially, the spacecraft is the Jupiter Near-polar Orbiter. It’s called Juno because of the tales of Greek and Roman mythology.

Juno was the wife of Jupiter, the king of the gods who visited other worlds and used clouds to hide his mischief. But Juno was able to look through them to see what Jupiter was up to. That’s what the spacecraft will do as it orbits the giant planet from as low as 3,000 miles above the clouds.

“When you see a picture of Jupiter, you’re seeing cloud tops that form the outer reaches of the atmosphere,” Steffes said. “It’s like seeing a veneer. You’re not seeing deep down.”

To sense what’s below those clouds, Steffes and his peers are utilizing Juno’s microwave radiometer (MWR) instrument. It measures radio waves from Jupiter’s deep atmosphere, providing a first-ever glimpse of what the planet is made of.

Steffes says microwave radio waves are similar to cellphone signals, which are constantly modified by clouds, rain, and gases.

“If you look at the bars on your phone as you walk next to a fish tank, you’ll notice you’ll have fewer bars. The water absorbs the radio energy from the cell tower to your phone,” he said. “Just like the cellphone idea, we’re going to measure the microwave radiation — the signals coming out of the atmosphere. Based on how they’re affected by the clouds and gases, we’ll know what’s down there.”

While revealing levels of hydrogen, ammonia, and other atmospheric components, Juno will discover the depths of Jupiter’s bands and clouds that are scattered high in the atmosphere. This includes the famous Great Red Spot, which has swirled on the planet for more than 300 years and is two to three times as large as Earth.

NASA image - planet Jupiter's giant red spot

Jupiter’s Great Red Spot as seen by Voyager I in 1979. Juno’s closest approach to Jupiter will bring it within 2,600 miles, inside the radiation belts that block microwave detection from Earth. Image source: NASA/JPL

Now that Juno has found its home for the next year and a half, Steffes and his graduate student, Amadeo Bellotti, are beginning to decipher Juno’s information based on years of work atop Georgia Tech’s Van Leer Building. Steffes’ research group has performed more than 6,000 microwave measurements to simulate the Jupiter atmosphere in their pressure vessel, which is located inside an oven on the roof of the building. They are trying to match Juno’s planetary data with their lab simulations.

“Our measurements cover a variety of pressures, temperatures, and compounds that Juno will likely find during its mission,” Bellotti said. “This portfolio of possible signatures will, at first look, give us a sense of the elements and compounds that form Jupiter’s atmosphere. Over a period of years, we’ll discover the actual mixture of different constituents in the atmosphere.”

The MWR is just one of Juno’s nine instruments. The others, which Georgia Tech is not associated with, will help determine the core of the planet; map magnetic and gravity fields; explore the planet’s poles, auroras, and magnetosphere; and take pictures from never-before-seen vantage points.

Jupiter contains more material than every other planet, comet, and asteroid in the solar system combined. It was the first planet to form, and scientists believe it can unlock countless mysteries of the solar system’s formation.

“I think we may discover that conditions vary from location to location,” Steffes said. “For example, conditions under the Great Red Spot could be totally different from the rest of the planet. These next 18 months will be very interesting and exciting.”

Jason Maderer is assistant director of Georgia Tech’s media relations team. He is a former television reporter.

Video: Paul Steffes describes Juno's mission


Since his arrival at the Georgia Tech School of Electrical and Computer Engineering (ECE) in 1982, Paul Steffes has had substantial support from NASA to develop techniques for using microwave systems to remotely sense the composition and structure of planetary atmospheres.

His research has supported Magellan-Venus, which mapped the surface of Venus and determined the topographic relief of the planet; Pioneer Venus, which investigated the solar wind in the Venusian environment, mapped the planet’s surface through a radar imaging system, and studied the characteristics of the upper atmosphere and ionosphere; and Juno, with which he has been involved since 2005. Juno’s goals are to understand the origin and evolution of Jupiter, look for a solid planetary core, map its magnetic field, measure water and ammonia in its deep atmosphere, and observe auroras.

photo - Paul Steffes standing in front of workbench with electronic instrumentsPaul Steffes in his lab. Photo by Fitrah Hamid.

In addition to support for the Juno mission in particular, Steffes’ research in this area has been supported by NASA under a continuous, single-subject grant for more than 31 years, making it the longest-running NASA research program at Georgia Tech. His total career support for all of his solar system research activities totals $5.5 million. He and his team have produced 160 journal and conference papers, and he has graduated 14 Ph.D. students who have published dissertations that focus on this area.

Over the years, Steffes has also worked on the design and implementation of Earth-based microwave and millimeter-wave measurements of the emissions from planets, using facilities such as the National Radio Astronomy Observatory’s Very Large Array (VLA), the largest single-site radio telescope in the world, located west of Socorro, New Mexico. In 1991, Steffes was selected by NASA to serve on the investigator team of the High Resolution Microwave Survey, a program to search for artificial microwave signals characteristic of civilizations outside our solar system. When Congress acted to terminate the program in 1993, a new donor-funded program for the search for extraterrestrial intelligence was begun by the SETI Institute in Mountain View, California.

Steffes’ leadership in planetary atmospheric research has been recognized by several national and international groups and at Georgia Tech. In 2011, the American Association for the Advancement of Science (AAAS) elevated him to the level of Fellow “for contributions to the understanding of planetary atmospheres through innovative microwave measurements,” and in 2004, he was elevated to IEEE Fellow “for contributions to the understanding of planetary atmospheres.” In 1996, Steffes received the IEEE Judith A. Resnik Award “for contributions to an understanding of the Venus atmosphere through innovative microwave measurements.”

NASA also recognized the level of Steffes’ contributions by naming him to the NASA Advisory Council (Planetary Science Subcommittee) in 2010 and to several mission selection panels. Steffes has also chaired several NASA research grant selection panels and subpanels. At Georgia Tech, he was recognized with the ECE Distinguished Faculty Achievement Award in 2010 and the D. Scott Wills ECE Distinguished Mentor Award in 2015. — Jackie Nemeth


rendering of Jupiter's layersThe first look into Jupiter’s clouds by the microwave radiometer.

Juno’s principal goal is to understand the origin and evolution of Jupiter. Underneath its dense cloud cover, Jupiter safeguards secrets to the fundamental processes and conditions that governed our solar system during its formation.

With its suite of science instruments, Juno will investigate the existence of a solid planetary core, map Jupiter’s intense magnetic field, measure the amount of water and ammonia in the deep atmosphere, and observe the planet’s auroras.

Juno will let us take a giant step forward in our understanding of how giant planets form and the role these titans played in putting together the rest of the solar system. — NASA/JPL



Determine the abundance of water and place an upper limit on the mass of Jupiter’s possible solid core to decide which theory of the planet’s origin is correct.


Understand Jupiter’s interior structure and how material moves deep within the planet by mapping its gravitational and magnetic fields.


Map variations in atmospheric composition, temperature, cloud opacity, and dynamics to depths greater than 100 bars at all latitudes.


Characterize and explore the three-dimensional structure of Jupiter’s polar magnetosphere and auroras.

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