Observation of discontinuities accompanied by interplanetary shock within the Martian magnetosheath

As fast forward interplanetary (IP) shocks travel outward in the IP medium, they might encounter planetary bow shocks (BSs) and then propagate into the magnetosheath. The interaction of an IP shock with a BS could create a new discontinuity, which has been predicted by theory and simulations, and commonly observed at Earth. Nevertheless, it is still uncertain whether such a phenomenon occurs at unmagnetized planets like Mars. Here, we present the first experimental observation of a discontinuity-like structure that follows a transmitted IP shock within the Martian magnetosheath. This event was recorded by the MAVEN spacecraft on March 3, 2015. The comparison of spacecraft measurements with theoretical studies indicates that the discontinuity-like structure is a compound structure in nature, composed of the slow expansion wave, contact discontinuity, and slow shock, launched by the interaction of a fast IP shock with the Martian BS. The results shed light on the similarities between magnetized and unmagnetized planets in response to the passage of IP shocks.