The Juno Mission and Jupiter Mysterious Winds

Data analysis of the NASA Juno mission reveals the details of the gravitational field of the giant planet and the intense winds that blow up to 3000 kilometers of depth below the surface of Jupiter, involving huge amounts of matter.

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Gravitational field, atmospheric flows, internal composition and polar cyclones: four different studies published in "Nature" trace an updated identikit of the planet Jupiter thanks to the vast amount of data collected by the NASA probe Juno, entered in polar orbit around the gas giant in the July 2016.

In the first study, Luciano Iess of Sapienza University of Rome and colleagues of an international collaboration, which also includes the University of Bologna and Pisa, have reconstructed the gravitational acceleration of Juno along its elliptical orbit around the planet by measuring the Doppler movements , that is, changes in the frequency of radio waves sent to Earth.

Minuscule anomalies in these signals reveal slight deviations of the probe's share along its orbit and, indirectly, the details of the mass distribution of Jupiter, responsible for the local variations of its gravitational field.

The most surprising result is that there is a component of the gravitational field of the planet that does not show a symmetry between the northern hemisphere and the southern hemisphere, as would be expected. This confirms that Jupiter does not behave like a solid body, due to the presence of imposing flows of matter on its surface and inside it.

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In the second study , Yohai Kaspi of the Weizmann Institute of Science in Rehovot, Israel, and international collaboration colleagues, including the Department of Mechanical and Aerospace Engineering at Sapienza University of Rome, show that the characteristic asymmetry of the Jerry gravitational field is the fruit of an equally asymmetric distribution of surface winds, which blow with different velocities to vary in latitude.

To influence the gravitational field of the planet, the winds must be relatively deep and involve a considerable amount of mass. This implies that the characteristic colored bands of Jupiter are not just a surface phenomenon, a discovery that puts an end to a long-running debate among paleontologists on the nature of these bands.

The analysis of the data shows in particular that the intensity of the wind decays slowly going deep until about 3000 kilometers below the surface of Jupiter, a share at which the pressure is about 100,000 times that of the atmosphere at the surface level terrestrial. The volume of Jupiter in which these winds are produced represents about 1 percent of the planet's mass.

The third study , based on Tristan Guillot in Nice and colleagues from an international collaboration, focused on the 3000 meters below the surface. The data analyzed by the authors show that this dimension marks a discontinuity: below, the deep interior of Jupiter consists of a fluid mixture of hydrogen and helium, which rotates like a solid body. In fact, the pressure is so high that hydrogen splits into positive ions (protons) and free electrons. These particles generate intense viscous friction forces that suppress winds in all directions.

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In the fourth study , Alberto Adriani of the National Institute of Astrophysics (INAF) of Rome and colleagues of an international collaboration, including the University of Bologna and the CNR-Institute of Atmospheric Sciences and Climate of Bologna and Rome, report the results of extensive observations in the infrared and visible spectrum of the Jupiter's polar regions conducted by Juno.

These regions are scarcely unknown, as they are not visible from Earth and have never been observed by space probes, which typically do not deviate from the equatorial regions of the giant planet.

The data show that the cyclones observed in these regions are arranged in such a way as to form polygonal patterns that persist over time. At the north pole, eight circumpolar cyclones revolve around a single cyclone, while at the south pole it observes the same pattern with a central cyclone and another five around. The origin of these cyclones and the physical mechanisms that lead them to be arranged in geometric shapes for now escape any physical explanation.

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