Autocorrelation Infrasound Interferometry on Mars.

A high‐sensitivity pressure sensor was deployed as part of the Mars Interior Exploration using Seismic Investigations, Geodesy and Heat Transport lander on Elysium Planitia in November 2018. We use pressure records from 1 October to 31 December 2019 (Sol 301–389) for frequencies between 0.1 and 0.5 Hz to infer relative sound‐speed changes in the Martian atmosphere using the autocorrelation infrasound interferometry method. We find that relative sound‐speed changes are up to ±15%, follow a similar pattern to Martian‐daily variations of atmospheric temperature and horizontal wind velocity, and are similar to those inferred from in‐situ observations and Martian climatology. The relative sound‐speed changes and horizontal wind speed variations are synchronous, while temperature peaks ∼1.88 hr after these time series. The strong and continuous emergence of coherent phases in the autocorrelation codas suggests the presence of continuous infrasound on Mars. Plain Language Summary: We study the Martian atmosphere using the pressure data collected by the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander. We apply a novel method to determine relative changes of sound‐speed, which in turn are related to changes in wind velocity and atmospheric temperature. Compared to Earth, Mars daily variations of sound‐speed are ∼10 times larger and the attenuation of acoustic waves is ∼2 orders of magnitude higher. Nevertheless, inferred relative sound‐speed changes are highly similar to temperature and horizontal wind velocity time series. Our analysis also indicates that the pressure sensor onboard the InSight lander samples a persistent background acoustic signal, which permits continuous monitoring of the highly variable Martian atmosphere. Key Points: Autocorrelation infrasound interferometry retrieves relative sound‐speed changes from the pressure data recorded by the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport landerIn the Martian atmosphere, the relative sound‐speed changes are up to ±15% and follow a similar trend to temperature and wind velocityPersistent emergence of coherent phases in the autocorrelation codas suggests the presence of continuous infrasound on Mars [ABSTRACT FROM AUTHOR]