2013ApJ...764...19B

Hubble Space Telescope transit observations in the near-UV performed in 2009 made WASP-12b one of the most "mysterious" exoplanets; the system presents an early ingress, which can be explained by the presence of optically thick matter located ahead of the planet at a distance of ∼4-5 planet radii. This work follows previous attempts to explain this asymmetry with an exospheric outflow or a bow shock, induced by a planetary magnetic field, and provides a numerical solution of the early ingress, though we did not perform any radiative transfer calculation. We performed pure 3D gas dynamic simulations of the plasma interaction between WASP-12b and its host star and describe the flow pattern in the system. In particular, we show that the overfilling of the planet's Roche lobe leads to a noticeable outflow from the upper atmosphere in the direction of the L₁ and L₂ points. Due to the conservation of the angular momentum, the flow to the L₁ point is deflected in the direction of the planet's orbital motion, while the flow toward L₂ is deflected in the opposite direction, resulting in a non-axisymmetric envelope, surrounding the planet. The supersonic motion of the planet inside the stellar wind leads to the formation of a bow shock with a complex shape. The existence of the bow shock slows down the outflow through the L₁ and L₂ points, allowing us to consider a long-living flow structure that is in the steady state.