On July 4, the veil over Jupiter’s mysteries will be ripped away with the arrival of NASA’s Juno mission, and Cornell University astronomer Jonathan Lunine will be there to watch it happen.
Like cosmic archaeologists, astronomers will use Juno’s instruments to understand what went into the icy planetesimals that Jupiter swept up after it formed. “It’s a unique record for the outer solar system of what these protoplanets might have been like,” says Lunine, the David Duncan Professor in the Physical Sciences in Cornell’s College of Arts & Sciences. “We’re doing the astronomical equivalent of ‘broken pottery’ archaeology, trying to piece back together the original molecules and ice grains that got evaporated and dissociated inside Jupiter billions of years ago.”
According to NASA, the primary goal of the Juno mission is to improve understanding of Jupiter’s formation and evolution. The spacecraft will investigate the planet’s origins, interior structure, deep atmosphere and magnetosphere. NASA officials say Juno’s study of Jupiter will help explain the history of our solar system and provide new insight into how planetary systems form and develop in our galaxy and beyond.
As a co-investigator on Juno, Lunine is attached to a working group rather than a specific scientific instrument; Lunine “floats” between several instruments. One is the Microwave Radiometer (MWR), designed to use radio wavelengths to achieve what the Galileo probe was unable to do 20 years ago: measure the water abundance in Jupiter below the clouds. Knowing this measurement will enable scientists to assess what materials Jupiter absorbed early in the solar system’s life.
Another of the instruments Lunine is interested in is the spacecraft itself, which will be used for a gravity experiment involving the Doppler effect to determine whether Jupiter has a solid core or not. Juno will swing so close to Jupiter for the measurement that it will be below the massive radiation belts, just a few thousand kilometers above the clouds.
Having spent his career trying to understand how the solar system formed, for Lunine, the spacecraft’s arrival at Jupiter is particularly fraught. “This is really the first mission that’s devoted to understanding the kingpin of the solar system, which played such a huge role in what happened early on in the history of the solar system,” he says. “It’s our first chance to look inside Jupiter with very, very powerful techniques.
The other instrument Lunine will be working with is the Juno Infrared Auroral Mapper (JIRAM), a near infrared spectrometer. It will detect water and certain trace gasses in the atmosphere to help determine its composition and will serve as a complement to the other two instruments on which Lunine will be working.
“One of the reasons I’m so excited about Juno is that this is a critical step in understanding not just how one solar system formed but how many planetary systems formed,” adds Lunine, who is a member of Cornell’s Carl Sagan Institute. He plans to compare what’s learned about the elemental composition of Jupiter to giant planets around other stars, to aid in understanding whether they formed the same way as Jupiter.
