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OUTER SOLAR SYSTEM

JunoCam looks at the Great Red Spot

The camera on board the spacecraft has captured dynamics of the wel-known storm that rages on Jupiter. The study is published on The Astronomical Journal

Jupiter’s Great Red Spot, an exceptionally long-lived storm churning south of Jupiter’s equator, has been observed continuously for nearly two centuries. Though this atmospheric vortex is the largest and longest-lived of any planet in our solar system, our observations suggest that the Great Red Spot is gradually shrinking: the major axis of the ellipse was ~21° in longitude 40 years ago, and only ~14° in the last few years. 

Our current understanding of the morphology of this storm comes primarily from detailed observations by spacecraft since 1979 - first by the two Voyager spacecraft as they flew by, then by the Galileo orbiter, and then by the Hubble Space Telescope. These past observations have ranged in resolution from about 15 to 150 km per pixel. Now, since the 2016 arrival of the Juno spacecraft in orbit around Jupiter, there’s a new player in town: JunoCam

JunoCam is a visible-light camera with a 58° field of view. In a new study on The Astronomical Journal, a team of scientists led by Agustín Sánchez-Lavega (University of the Basque Country, Spain) have used the unprecedented detail of JunoCam’s observations to examine the various cloud morphologies inside the Great Red Spot

Sánchez-Lavega and collaborators identify five particular morphologies within the cloud tops of the Great Red Spot.

Compact cloud clusters: Several groups of compact clouds resemble altocumulus clouds observed on Earth. These may suggest condensation of ammonia. 

Mesoscale waves: Interfering trains of wave packets indicate stable conditions in this region. 

Spiraling vortices: A large eddy of ~500 km in radius suggest a region of intense horizontal wind shear. 

Central turbulent nucleus: The red nucleus of the Great Red Spot spans ~5.200 km in length (that’s about 40% of Earth’s diameter) and ~3.150 km in width. 

Large dark thin filaments: Undulating dark gray filaments 2.000 - 7.000 km in length circulate at high speeds around the outer park of the vortex. These may be darker aerosols or represent areas with different altitudes. 

The team’s measurements of the overall wind field in the Great Red Spot demonstrate that though the Spot may be dramatically shrinking, its wind field has shown little change over 40 years of observation. The rich variety of morphologies we’re seeing therefore likely represents just the top of a dynamical system with a much deeper circulation. 

Juno's goal is to analyse the Jupiter’s characteristics as representative of the giant planets. The Solar System’s ‘heavyweight’ can, in fact, offer fundamentally important data not only for gaining deeper knowledge of the origin of the System itself, but also for analysing those of the planetary systems that are gradually discovered around other stars, with particular reference to those exoplanets that have a similar mass to that of Jupiter. 

Juno's heart is the Italian Jiram (Jovian InfraRed Auroral Mapper), financed by ASI, built by Leonardo and operated under the scientific responsibility of INAF's Institute of Astrophysics and Planetology (IAPS). Juno's other Italian component is KaT (Ka-Band Translator), a radio science instrument designed by the 'La Sapienza' University of Rome, built by Thales Alenia Space Italia (A Thales/Leonardo-Finmeccanica company) again with ASI's support.