The Search for Exoplanets using Ultra-long Wavelength Radio Astronomy

Recent studies on extra solar planets (exoplanets) provide us with a new glimpse into the Milky Way's composition. Exoplanets appear to be very typical around Sunlike stars. Most of these exoplanets are observed via indirect measurements. If a direct radio observation of the exoplanet's signal was possible, new scientific information will help us in the search for Earth like planets. Magnetised exoplanets are expected to emit strongly at radio wavelengths, in the same way as magnetised planets in our own solar system. Direct radio observations of exoplanets, therefore, will give important additional information to science. It would confirm that the planet has a magnetic field and it will also put a limit on the magnetic field strength near the surface of the planet. The determination of circular polarisation would indicate the source of the magnetic hemisphere and would give limits on the plasma density in the magnetosphere. However, not a single exoplanet radio detection have been measured until now. There are two reasons for this: the weakness of the signal and the frequency range in which the signal will appear - very low frequencies. The only solution to detect these weak signals from exoplanets is to realise a space-based radio telescope. Space based ultra-long wavelength radio astronomy has recently gained interest. The need for large effective apertures spread over long ranges implies that advanced technologies are required, which is in reach at this moment. This together with the unexplored frequency band below 30 MHz makes these initiatives very interesting. A space or Lunar based low-frequency radio array would suffer significantly less from the limitations and hence would open up the last, virtually unexplored frequency domain in the electromagnetic spectrum. In this paper we will present the development of a space-based radio telescope for detection exoplanets in the ultra-long wavelength range. This includes a system concept, and the algorithms to be used as a direct exoplanet radio observatory.