The passage of a radio signal through a planetary atmosphere, ionosphere, or magnetosphere affects the polarization, frequency, and power of the radio signal. Radio occultations are a common experiment used to measure planetary atmospheres, but they traditionally rely on radio transmissions from a spacecraft near the planet. We explore whether similar measurements of planetary and exoplanetary environments can be made using distant astrophysical radio sources such as pulsars, active galactic nuclei, and masers. We find that occultations by solar system planets, such as Jupiter, can be used to measure planetary magnetic field strength, plasma density, and neutral density. Based on the number of known distant astrophysical radio sources, occultations by solar system planets are likely to occur often. Occultations are most likely when the solar system planets are near the intersection of the ecliptic and galactic planes. For even the closest exoplanetary systems, the low probability of alignment of the Earth, an exoplanet, and a suitable distant astrophysical radio source presents a considerable challenge. The concentration of both exoplanets and galactic radio sources in the galactic plane may alleviate this challenge somewhat, but it still appears formidable. An alternative type of occultation may be more promising for exoplanets: high-resolution radio imaging of an exoplanet as it transits in front of its parent star.
Radio Exploration of Planetary Habitability (AASTCS5)
- Pub Date:
- May 2017