Spacecraft radio signals as plasma probes

Near solar conjunction, a spacecraft signal passes close to the Sun. Density irregularities carried by the solar wind broaden the received Doppler spectrum, and the width of that spectrum scales with the wind speed and the density fluctuation level. I derive both quantities from S-band data of the Indian Mars Orbiter Mission and X-band data of Akatsuki, including the 2016 and 2022 Akatsuki conjunctions at different levels of solar activity.

Conventional retrievals fix the turbulence spectral index in advance. The framework published in MNRAS (2026) removes this assumption, and the method in Advances in Space Research (2026) generalises the retrieval for a Kolmogorov spectrum.

ApJ 2025MNRAS 2025MNRAS 2026VideoASR 2026

Radio occultation retrievals attribute frequency fluctuations to the atmosphere or ionosphere of the target body. Part of the fluctuation arises in the interplanetary medium between Earth and the spacecraft. I measure this contribution with five datasets: two-way S-band Chandrayaan-3 data outside the lunar ionosphere, two-way S-band Chandrayaan-2 data during lunar occultation, one-way S/X-band Venus Express (VeRa) and Akatsuki data under interplanetary-only conditions, and one-way X-band Akatsuki data during solar occultation.

Icarus 2026Video

Two-way coherent S-band measurements from the Chandrayaan-2 Radio Science experiment give electron density fluctuations integrated along the Earth–Moon line of sight. Comparing orbits with the Moon in the solar wind against passages through the terrestrial magnetotail separates the turbulence of the two plasma regimes.

JGR: Planets 2026Video

As a member of the JWST Transiting Exoplanet Community Early Release Science team, I am a co-author on the first JWST spectra of the hot Jupiter WASP-39b, which report carbon dioxide, carbon monoxide and photochemically produced sulphur dioxide, and on related studies of WASP-18b and WASP-43b.

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Co-author on three white papers for the 2024–2033 Solar and Space Physics Decadal Survey, including the COMPLETE flagship concept for three-dimensional measurement of coronal magnetic energy storage and release, and second author of the UK white paper on magnetic reconnection (2025).

White papers