FARSIDE (Farside Array for Radio Science Investigations of the Dark ages and Exoplanets) is a Probe-class mission to place a low radio frequency interferometric array on the farside of the Moon. A NASA-funded design study, focused on the instrument, a deployment rover, the lander and base station, delivered an architecture consistent with the mass and cost requirements for a Probe mission. This architecture consists of 128 dual polarization antennas deployed across a 10 km area by a rover, and tethered to a base station for central processing, power and data transmission to the Lunar Gateway. FARSIDE will provide the capability to image the entire sky each minute in 1400 channels spanning frequencies from 200 kHz to 40 MHz, extending down two orders of magnitude below bands accessible to ground-based radio astronomy. The lunar farside can simultaneously provide isolation from terrestrial radio frequency interference, auroral kilometric radiation, and plasma noise from the solar wind. It is thus the only location within the inner solar system from which sky noise limited observations can be carried out at sub-MHz frequencies. This will enable near-continuous monitoring of the nearest stellar systems in the search for the radio signatures of coronal mass ejections and energetic particle events, and will also detect the magnetospheres for the nearest candidate habitable planets. Simultaneously, FARSIDE will be used to characterize similar activity in our own solar system, from the Sun to the outer planets, including the hypothetical Planet Nine. Through precision calibration via an orbiting beacon, and exquisite foreground characterization, FARSIDE will also measure the Dark Ages global 21-cm signal at redshifts z~50-100. The unique observational window offered by FARSIDE will enable an abundance of additional science ranging from sounding of the lunar subsurface to characterization of the interstellar medium in the solar system neighborhood.
Gregg Hallinan is Professor of Astronomy at Caltech, and Director of the Owens Valley Radio Observatory (OVRO). His primary interests are the magnetic fields of exoplanets, brown dwarfs and stars and all sources of transient radio emission.