Explained in 60 Seconds: Surveys ’s Great

Column Red Spot and the Citizen-Led Approach to Imaging

Glenn S. Orton Senior Research Scientist Jet Propulsion Laboratory California Institute of Technology Glenn.S.Orton@jpl..gov

The Juno spacecraft is blazing a new trail in understanding Jupiter’s atmosphere and magnetosphere (Daniels, 2016). Juno scientists have been keenly anticipating observations of Jupiter’s Great Red Spot, a storm the size of two or three Earths that has been raging for over a century. Juno passed directly over the centre of Jupiter’s Great Red Spot on 11 July 2017, only 9000 kilometres away from the tops of its clouds.

The highest-resolution image of the Great Red Spot has an unprecedented spatial scale of six kilometres per pixel. V-shaped lanes, darker in colour, mark peak veloci- ties in the Great Red Spot’s counterclock- wise rotation, and smaller anti-clockwise vortices can also be seen. Near the cen- Figure 2. Close-up of the Great Red Spot showing tre of the spot are clusters of clouds 25–30 the mesoscale gravity wave and thunderstorm-like kilometres in size, reminiscent of terrestrial bright clouds. Annotations courtesy of CAPjournal. thunderstorms. Near the northern edge of the Great Red Spot, as the red colour fully produced images that enhance fea- blends into the whiter-coloured, slower-­ tures without introducing spurious pro- moving clouds, is a long series of ­linear cessing effects. For example, the striking features spaced about 70 kilometres from figure in this article was created by Gerald each other. This is the first evidence for Eichstädt, a mathematician in Stuttgart, small-scale atmospheric waves called Germany, with enhancements by Seán Mesoscale Gravity Waves within the Great Doran, a visual artist in London. Red Spot. Gravity waves happen when the atmosphere gets disturbed. The force Soon, the information from JunoCam will of gravity pulls the atmosphere back into be assembled along with Juno’s other equilibrium, but ripples are left behind. observations as well as results from a coor- These ripples are gravity waves. dinated campaign of Earth-based sup- porting observations to extend and sup- Although most of Juno’s instruments col- port Juno’s results. Much is owed to the lect data that need to be downloaded citizen-scientists who helped to track the and processed by a science team before location of the Great Red Spot and pro- they can be made widely available, the vided detailed processing of Juno’s initial results from Juno’s public-outreach cam- results. era, JunoCam, became available to both the science team and the general pub- This research was carried out at the Jet lic within a couple of days of the close Propulsion Laboratory, California Institute approach and captured jaw-dropping of Technology, under a contract with moments. Originally intended only as a the National Aeronautics and Space public-outreach instrument, JunoCam has Administration. no dedicated science–analysis team, but Figure 1. The highest-resolution colour-composite the images have proven to be very useful. image of Jupiter’s Great Red Spot by the JunoCam References In fact, astronomers are particularly grate- instrument. Credit: NASA/Southwest Research ful to talented members of the public who Institute/Malin Space Science Systems/Gerald Daniels, Sebastian. CAPjournal 21, December have processed the raw frames and care- Eichstädt, Seán Doran 2016

4 CAPjournal, No. 23, February 2018