On the Fourth of July, Paul Steffes will stare into the Pasadena, California, evening sky. He will not look for fireworks. Instead, his gaze will focus on the heavens while his ears brace for a beep generated 520 million miles away.
Steffes, a professor in the Georgia Tech School of Electrical and Computer Engineering, is a member of the Juno Science Team. He’ll be in California with fellow team members on Independence Day as the spacecraft reaches its destination: Jupiter. The mission will improve our understanding of the birth of the solar system and the mysteries of its largest planet.
Juno arrives in Jupiter’s orbit five years after NASA and the Jet Propulsion Lab launched it and 11 years after a team, including Steffes, created it.
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.
Measuring microwave radiation
“When you see a picture of Jupiter, you’re seeing cloud tops that form the outer reaches of the atmosphere,” says Steffes. “It’s like seeing a veneer. You’re not seeing deep down.”
To sense what’s below those clouds, Steffes and his peers will utilize Juno’s microwave radiometer (MWR) instrument. It will measure 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 says. “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.
A 47-minute delay
Steffes and graduate student Amadeo Bellotti will both be in Pasadena for Juno’s July 4 orbital insert. They’ll standby as Jupiter’s massive gravity pulls in the basketball court-sized spacecraft at a speed of more than 40 miles per second. Juno will counteract that force by using its engines to place itself into a polar orbit around the planet. It takes about 47 minutes for the machine to communicate with Earth, meaning the scientists will have to hold their breath as they wait for conformational beeps that Juno was successful in its tug-of-war maneuver.
Once Juno finds its orbit, the professor and student will wait until late August for the first MWR data. Then they’ll begin 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. Once they receive the planetary data, they’ll match it with their lab simulations.
“Our measurements cover a variety of pressures, temperatures, and compounds that Juno will likely find during its 20 months in orbit,” says Bellotti. “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, the work of other teams, 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’re going to be surprised by what we find,” says Steffes. “I think we may discover that conditions vary from location to location. For example, conditions under the Great Red Spot could be totally different from the rest of the planet. It will be very interesting and exciting.”
Ride along with Juno with NASA’s “Eyes on Juno” app.
Image Source: Screenshot of Georgia Tech YouTube Channel