New Models of Jupiter's Magnetopause and Bow Shock Through the Juno Prime Mission: Probabilistic Location, Shape, and Internally‐Driven Variation.

The interaction between Jupiter's magnetosphere and the solar wind is not well‐constrained: while internal energetic plasma processes are thought to dominate plasma circulation, the solar wind nonetheless exerts significant control over the shape and scale of the whole structure. To better constrain this interaction, we derive new functional forms for Jupiter's magnetopause and bow shock using data from the Ulysses, Galileo, Cassini, and Juno missions and calibrated solar wind estimates from the Multi‐Model Ensemble System for the Heliosphere (MMESH). We design an empirical Bayesian model to estimate the locations of the boundaries using a Markov‐chain Monte Carlo (MCMC) algorithm, expanding our model to sample all times, not only boundary crossing events. The boundary surfaces which best describe the data are thus estimated without the need for a full, physics‐based magnetohydrodynamic (MHD) treatment of the Jovian magnetosphere and the additional assumptions required for such. The new magnetopause model exhibits significant polar flattening and dawn‐dusk asymmetry, and includes a narrowing of the magnetotail when compared to previous models. The new bow shock model is largely axisymmetric. Both boundary models describe surfaces which lie closer to Jupiter than previous models, which has important implications for the modern picture of Jupiter's dynamic magnetosphere and the expected science results of current and upcoming Jupiter‐bound spacecraft. Applying these models to Juno's trajectory, we estimate that the spacecraft should be expected to spend ∼19% ${\sim} 19\%$ of each orbit in the magnetosheath and ∼4% ${\sim} 4\%$ of each orbit in the solar wind starting from Perijove 64 (PJ64, 21 July 2021). Plain Language Summary: The solar wind, a perpetual stream of plasma and magnetic fields flowing outwards from the Sun in all directions, interacts with all of the planets as it flows past them. Planets with their own internal magnetic fields create bubbles within this solar wind flow—magnetospheres—which are supported by the balance of pressures inside and outside. At most planets, a second boundary forms around the magnetosphere—a bow shock—caused by the fast‐flowing solar wind suddenly stopping as it hits the magnetosphere. The shapes and sizes of a planet's magnetosphere and bow shock are continuously changing as the solar wind changes, and understanding these changes is important for determining how mass and energy move through space near that planet. Here, we investigate the size and shape of Jupiter's magnetosphere and bow shock using spacecraft measurements and solar wind models, and define new functions that describe how the shapes change with the solar wind. The new shape of the magnetosphere is asymmetric, being flatter near the poles and inflated near dusk. The sizes of both the magnetosphere and the bow shock are smaller than previously thought, meaning that current missions to Jupiter, like Juno, will leave the magnetosphere and bow shock more frequently. Key Points: New, data‐driven boundary models for Jupiter's magnetopause and bow shock surfaces are derived using Bayesian statistical techniquesThe estimated magnetopause is polar‐flattened (∼15%) and asymmetric in the dawn‐dusk direction; the estimated bow shock is mostly symmetricJuno will likely spend 10× longer in the solar wind during the extended mission compared to estimates from earlier boundary models [ABSTRACT FROM AUTHOR]