Observation of solar radio burst events from Mars orbit with the Shallow Radar instrument

¹ University of Texas at Austin Institute for Geophysics, J.J. Pickle Research Campus, 10100 Burnet Road, 78758 Austin, TX, USA
e-mail: christopher.gerekos@austin.utexas.edu
² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91011, USA
³ Department of Physics and Astronomy, University of Turku, Turku, Finland
⁴ Naval Postgraduate School, Monterey, CA, USA
⁵ Fondazione Bruno Kessler, Via Sommarive 18, 38123 Povo, Trento, Italy
⁶ School of Physics and Astronomy, University of Leicester, University Rd, Leicester LE1 7RH, UK
⁷ Center for mathematical Plasma Astrophysics, Department of Mathematics, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁸ Solar-Terrestrial Centre of Excellence, Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Uccle, Belgium
⁹ Department of Aerospace Engineering Sciences, College of Engineering and Applied Sciences, University of Colorado Boulder, Boulder, CO, USA

Received: 7 September 2023
Accepted: 19 December 2023

Abstract

Context. Multispacecraft and multiwavelength observations of solar eruptions, such as flares and coronal mass ejections, are essential to understanding the complex processes behind these events. The study of solar burst events in the radio frequency spectrum has relied almost exclusively on data from ground-based observations and a few dedicated heliophysics missions such as STEREO or Wind.

Aims. By reanalysing existing data from the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument, a Martian planetary radar sounder, we discovered the instrument was also capable of detecting solar radio bursts and that it was able to do so with unprecedented resolution for a space-based solar instrument. In this study, we aim to demonstrate the reliability and value of SHARAD as a new solar radio observatory.

Methods. We characterised the sensitivity of the instrument to type III solar radio bursts through a statistical analysis of correlated observations using STEREO and Wind as references. Using 38 correlated detections, we established the conditions under which SHARAD can observe solar bursts in terms of acquisition geometry. As an example of scientific application, we also present the first analysis of type III characteristic times at high resolution beyond 1 AU.

Results. A simple logistic model based purely on geometrical acquisition parameters can predict burst show versus no-show in SHARAD data with an accuracy of 79.2%, demonstrating the reliability of the instrument in detecting solar bursts and laying the foundation for using SHARAD as a solar radio observatory. The extremely high resolution of the instrument, both in temporal and frequency directions; its bandwidth; and its position in the Solar System enable SHARAD to make significant contributions to heliophysics. Notably, it could provide data on plasma processes on the site of the burst generation and along the propagation path of associated fast electron beams.