The Origin of Jupiter's Great Red Spot

Jupiter's Great Red Spot (GRS) is the largest and longest-lived known vortex of all solar system planets but its lifetime is debated and its formation mechanism remains hidden. G. D. Cassini discovered in 1665 the presence of a dark oval at the GRS latitude, known as the "Permanent Spot" (PS) that was observed until 1713. We show from historical observations of its size evolution and motions that PS is unlikely to correspond to the current GRS, that was first observed in 1831. Numerical simulations rule out that the GRS formed by the merging of vortices or by a superstorm, but most likely formed from a flow disturbance between the two opposed Jovian zonal jets north and south of it. If so, the early GRS should have had a low tangential velocity so that its rotation velocity has increased over time as it has shrunk. Jupiter's Great Red Spot (GRS) is probably the best known atmospheric feature and a popular icon among solar system objects. Its large oval shape, contrasted red color and longevity, have made it an easily visible target for small telescopes. From historical measurements of size and motions, we show that most likely the current GRS was first reported in 1831 and is not the Permanent Spot observed by G. D. Cassini and others between 1665 and 1713. Numerical models show that the GRS genesis could have taken place from an elongated and shallow, low speed circulation cell, produced in the meridionally sheared flow. A study of historical observations suggests that Jupiter's Great Red Spot (GRS) was not the Permanent Spot reported by G. D. Cassini in 1665 The temporal evolution of the shrinkage rate, area and eccentricity of the GRS and its Hollow have been precisely determined Observations and numerical simulations indicate that the genesis of the GRS was due to a disturbance in Jupiter's sheared flow