Identifying habitability of exoplanets through radio astronomy
Characterising the habitability of planets orbiting stars other than our Sun is essential for understanding life outside our own Solar System. A planet is defined to be habitable if it is located within an orbital distance such that the existence of liquid water on the planet’s surface is possible (which depends on the brightness of the star). However, an equally important factor for habitability is the stability of the planet’s atmosphere, necessary to regulate the surface temperature of the planet. Intense stellar magnetic activity, such as flares and wind, can erode the planet’s atmosphere and leave the planet uninhabitable. Strong planetary magnetic fields may mitigate the impact of the stellar magnetic activity.
In our own Solar System, the Earth has retained its atmosphere thanks to the protection provided by its strong magnetic fields. In contrast, Mars lacks a strong magnetic field structure and as a result suffers from significant atmospheric losses. Thus to evaluate the habitability of a planet, the magnetic field strengths of both the parent star and the planet must be known. Observations at radio frequencies provide a unique way to directly measure the magnetic field strengths of planets and stars.
CAASTRO researcher Dr Christene Lynch (University of Sydney) and colleagues use the Murchison Widefield Array (MWA) low-frequency radio telescope to investigate the impact of star-planet magnetic interactions on the habitability of planets orbiting low-mass stars. In a recent study, they report the detection of four low-intensity, polarised flares from the highly magnetically active low-mass star UV Ceti. Using the polarisation characteristics of the observed flares, they were able to identify the physical process that generated the flares – a first-ever achievement at these frequencies for these stars. Additionally, the team measured the detected radio emission to be associated with a fairly moderate magnetic field strength.
In a companion study, Dr Lynch and colleagues targeted the young Upper-Scorpius stellar association to make the first radio detection of a planet outside our Solar System. This survey is different from previous efforts in that it is the first to target planets orbiting stars that are still forming. Young planet systems are expected to be the best candidates for radio detections given the predicted higher magnetic field strengths and stronger and denser stellar winds. Their research paper reports the first upper limits on radio emission from planets in young stellar systems.
Christene Lynch, Emil Lenc, Tara Murphy et al. in The Astrophysical Journal Letters (2017): “154 MHz detection of faint, polarized flares from UV Ceti”
Christene Lynch, Tara Murphy et al. in The Monthly Notices of the Royal Astronomical Society (2017): “A search for circularly polarised emission from young exoplanets”