On September 7, the Juno spacecraft made the 54th close flyby of Jupiter, which allowed it to capture images with enhanced details in cloud features and colors.
Jupiter's Atmospheric Makeup
The violent nature of Jupiter's turbid atmosphere has long been a source of fascination for planetary scientists. The gas giant has no firm surface to touch down since its atmosphere essentially makes up the entire planet. Unlike the rocky planets, Jupiter is composed mainly of hydrogen and helium, with some traces of other gases like water vapor, methane, sulfur, and ammonia which comprise a tiny fraction of its air.
From the outermost edges towards the center of Jupiter, pressure and temperature go up, causing the gases to separate into layers. The hydrogen changes from gas to liquid in deeper regions and may even become metallic. Winds generally separate the surface of the planet and the layer resting on top of it, known as the troposphere.
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Exploring the Gas Giant With Radio Science
The atmosphere of Jupiter is one of the critical targets for NASA's Juno mission, which began orbiting the gas giant in 2016. During each of the 55 close flybys, astronomical instruments have peered below the planet's turbulent cloud deck to understand how Jupiter works from the inside out.
The mission gains insight into Jupiter's interior through radio science. Astronomers use NASA's Deep Space Network antennas to track the spacecraft's radio signal. As Juno flies past the planet near 130,000 mph (209,000 kph), the experts measure the tiny changes in its velocity, as small as 0.01 millimeter per second. Since these changes are due to the variations in Jupiter's gravity field, their measurements allow the mission to see into Jupiter's atmosphere.
To determine the nature of Jupiter's atmospheric winds, a group of experts applied a mathematical technique that models gravitational variations and surface elevations of rocky planets. In studying Jupiter, the method can be used in mapping the winds accurately at depth. Using high-precision data from Juno, the study authors generated a four-fold increase in the resolution over earlier models made by trailblazing explorers Galileo and Voyager.
Measuring the gravity field of the gas giant matched the old model, which determined the planet's powerful east-west zonal flows that extend from the cloud-level white and red zones. Additionally, the measurements also revealed that instead of extending in every direction like a radiating sphere, these zonal flows move inward cylindrically along the direction of Jupiter's rotation axis.
The structure of Jupiter's deep atmospheric winds has been questioned since the 1970s, and the Juno mission has finally settled this debate. According to study lead author Yohai Kaspi of the Weizmann Institute of Science in Israel, all 40 gravity coefficients measured by Juno matched their previous calculations of what was expected from the gravity fields if the winds whip around in cylindrical form.
The new gravity model application does not only improve the current understanding of Jupiter's internal structure and origin, but it also helps gain more insight into the atmospheres of other planets. Juno's mission is currently extended. As its journey progresses, astronomers are achieving scientific outcomes that define the gas giant, likely relevant for all gaseous planets within the Solar System and beyond.
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