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<p>Observations of Mercury’s sodium exosphere reveal a global annual variability, with higher total content enhancements occurring at the aphelion and perihelion. We identify the micro-meteoroid impact vaporization (MMIV) as a critical source of sodium, which can explain the observed yearly variability. This source is effective, yet with variable intensity throughout Mercury’s orbit, and it is asymmetric in a local-time reference frame, with a prevalence on the dawn side. Instead, in a fixed-longitude reference frame, the MMIV source is enhanced in two regions, located at 90° and 270° longitude at the equator, which we identify as "hot MMIV poles", in contrast to the so-called "cold poles" associated with the average temperature map. Using ground-based exospheric data from the THEMIS telescope and by employing a Markov Chain Monte Carlo method, we can rigorously test the significance of this asymmetric source and confirm this scenario. This model accurately captures both the magnitude and the seasonal patterns of Mercury’s Na exosphere. The results highlight the combined effect of Mercury’s rotation and revolution in modulating sodium source and loss processes, explaining the dawn-side enhancements observed by MESSENGER during Mercury’s outbound leg of the orbit, but not during the inbound one. Then, the "hot MMIV poles" hypothesis is tested with a full 3D model which now includes a new model for the surface temperature of Mercury, able to r: eproduce also the puzzling dusk-side sodium increase observed during Mercury’s inbound leg of the orbit.</p> Graphical Abstract <p></p>

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Hot poles at Mercury from micro-meteoroids weathering

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月26日

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  • A. Mura,
  • A. Milillo,
  • V. Mangano,
  • F. Leblanc,
  • M. Moroni,
  • S. Massetti,
  • G. Richards,
  • C. Plainaki,
  • A. Brin,
  • E. De Angelis,
  • P. Di Bartolomeo,
  • S. Orsini,
  • R. Rispoli,
  • R. Sordini,
  • M. Stumpo

摘要

Observations of Mercury’s sodium exosphere reveal a global annual variability, with higher total content enhancements occurring at the aphelion and perihelion. We identify the micro-meteoroid impact vaporization (MMIV) as a critical source of sodium, which can explain the observed yearly variability. This source is effective, yet with variable intensity throughout Mercury’s orbit, and it is asymmetric in a local-time reference frame, with a prevalence on the dawn side. Instead, in a fixed-longitude reference frame, the MMIV source is enhanced in two regions, located at 90° and 270° longitude at the equator, which we identify as "hot MMIV poles", in contrast to the so-called "cold poles" associated with the average temperature map. Using ground-based exospheric data from the THEMIS telescope and by employing a Markov Chain Monte Carlo method, we can rigorously test the significance of this asymmetric source and confirm this scenario. This model accurately captures both the magnitude and the seasonal patterns of Mercury’s Na exosphere. The results highlight the combined effect of Mercury’s rotation and revolution in modulating sodium source and loss processes, explaining the dawn-side enhancements observed by MESSENGER during Mercury’s outbound leg of the orbit, but not during the inbound one. Then, the "hot MMIV poles" hypothesis is tested with a full 3D model which now includes a new model for the surface temperature of Mercury, able to r: eproduce also the puzzling dusk-side sodium increase observed during Mercury’s inbound leg of the orbit.

Graphical Abstract