Shocklets in the vicinity of Mercury

Shocklets are compressive, linearly polarized magnetosonic structures that have been widely observed in the Earth's foreshock. They form due to wave steepening and dispersive effects, often accompanied by whistler wave precursors. At Earth these structures are characterized by steepened upstream edges, magnetic compression below 2, and associations with hot diffuse ion distributions. Shocklets play a crucial role in energy transfer and wave-particle interactions in collisionless shocks. While most studies have focused on Earth's foreshock, some evidence suggests their presence at Venus, raising questions about their existence in other planetary foreshocks.

In this study, we investigate the presence of shocklets in Mercury's foreshock using data from the MESSENGER mission. The timescales of Hermean shocklet candidates range from 3 to 30 seconds. Our preliminary analysis reveals that shocklets at Mercury exhibit greater diversity compared to those observed at Earth. While some structures resemble typical Earth-like shocklets, characterized by a sharp leading edge with whistler wave precursors followed by a slower relaxation, we also identify ULF magnetosonic waves accompanied by high-frequency fluctuations that display initial signs of wave steepening which could correspond to an early stage of the Earth-like shocklet. Our findings highlight the complex and dynamic wave activity in Mercury's unique solar wind environment.