# Martian ionospheric response during the May 2024 solar superstorm

## TL;DR

A solar flare in May 2024 caused Mars' lower ionosphere to expand by 278%, offering new insights into solar impacts on planetary atmospheres.

## Contribution

The study presents the largest observed expansion of Mars' lower ionosphere due to a solar flare, revealing a new relationship between soft X-ray flux and ionization.

## Key findings

- A solar flare caused Mars' lower ionospheric layer to expand 278% beyond its typical size.
- Soft X-ray irradiance increased threefold during the event.
- The ionization increase depends on the spectrum 'hardening' from the solar flare.

## Abstract

Solar energetic events can have considerable effects on planetary ionospheres. However, the erratic nature of these solar energetic events make observations difficult. Here we show a mutual radio occultation observation, which serendipitously occurred just 10 minutes after a large solar flare impacted Mars. This resulted in the largest lower ionospheric layer ever recorded, where it was 278% its typical size. We used in-situ soft x-ray irradiance measurements to show a threefold increase in flux. This infers a different relation of soft X-ray to this layer’s density than previously thought, with variations depending on the amount of spectrum ‘hardening’ leading to the increase of ionisation from secondaries.

The response of Mars’ ionosphere to major solar energetic events has been known, but such observations are challenging. Here, the authors show mutual radio occultation observations revealing that a solar flare in May 2024 enhanced the lowest ionospheric layer of Mars by 278% of its typical size.