“PAC does not overlap with other areas of interest to human activity. PAC is the only area of the far side that will never be reached by the radiation emitted by future space bases located at the L4 and L5 Lagrangian points of the Earth-moon system,”announced Claudio Maccone, chair of the Moon Farside Protection Permanent Committee, recounting the immediacy and potential of a new age of radio astronomy.
For decades, efforts to detect cosmic messages from the dawn of the universe have been stymied by the insistent interference of the radio noise of Earth. Even in the most distant corners of the globe, from the Antarctic subantarctic Marion Island to Nunavut in the Arctic, scientists have not been able to break free from the din of man-made radio frequency interference (RFI) and distortions caused by Earth’s ionosphere. As Jonathan Pritchard of Imperial College London explained, “When scientists first started doing 21 cm low-frequency astronomy, they described it as doing astronomy from the bottom of a swimming pool.” The metaphor captures the challenge of detecting the weak, redshifted 21-cm hydrogen line a spectral signature of the universe’s “cosmic dark ages” beneath the noisy cover of terrestrial interference.
This standoff has motivated a daring solution: to hear from the back of the Moon, where the mass of the Moon itself acts as a natural barrier to Earth’s radio emissions. The back is not only quiet; it is, according to University of Colorado Boulder’s Jack Burns, the only truly radio-quiet zone in the inner solar system the only truly radio-quiet zone in the inner solar system. Here, not just Earth-bound transmitters are blocked but also satellite megaconstellations and, at lunar night, even the Sun’s radio outbursts.
Leading the way in this lunar quantum leap is the Lunar Surface Electromagnetics Experiment-Night (LuSEE-Night), a miniature radio telescope engineered to work in the far side of the Moon. Designed by a consortium spearheaded by the US Department of Energy’s Brookhaven National Laboratory and NASA, LuSEE-Night will travel aboard Firefly Aerospace’s Blue Ghost 2 lander. The 3.3 x 3.3 x 2.3-foot device is designed to detect radio signals in the 0.1–50 MHz range, an uncharted spectral window from Earth because of absorption by the atmosphere and longer-than-10-meter interference wavelengths (lower than 30 MHz frequency). Its electronics consist of a 50-MHz Nyquist baseband receiver system and a radio spectrometer, allowing for accurate filtering and analysis of cosmic signals.
The engineering task is daunting. The 14-day lunar night freezes temperatures to –279.6°F, compromising sensitive electronics’ integrity. LuSEE-Night meets this challenge with an 88.2-lb lithium-ion battery reserved for heating and sustaining operational temperatures in the absence of solar power. This strategy leverages insights from terrestrial experiments conducted in extreme settings, like the solar-fuel cell hybrid systems built for Arctic radio arrays hybrid system that fused together solar panels and fuel cells and could energize the antenna over decades of Arctic winter.
LuSEE-Night’s scientific aspirations are as lofty as its technical challenges. By detecting ultra-long-wavelength radio waves, it attempts to investigate the universe’s “dark ages” the period following the formation of the cosmic microwave background but preceding the first stars turning on. The universe was full of neutral hydrogen, whose redshifted 21-cm line, as seen from Earth, provides a distinctive three-dimensional picture of early matter distribution measuring deviations in the signal can determine the distance to each emission point. Discovering these signals would shed light on the creation of the very first stars, galaxies, and black holes, and probe underlying theories of inflation, dark matter, and dark energy to advance our knowledge of fundamental particle physics, dark matter, dark energy and cosmic inflation.
But LuSEE-Night is just the start. Visionary schemes propose crater-scale radio telescopes on the far side of the moon, like the Lunar Crater Radio Telescope (LCRT), which would deploy a kilometer-diameter wire mesh reflector with autonomous wall-climbing robots deploy a wire mesh with wall-climbing DuAxel robots inside a 3-5 km diameter crater. The structure would be enormous even compared to the Arecibo and FAST telescopes, and would be sensitive to signals from the earliest epochs in the universe. The LCRT’s design has to contend with storage and deployment of the enormous mesh, structural and thermal stresses, and radio performance each a multifaceted systems engineering challenge in itself.
The cost for protecting the Moon’s far side as a sanctuary for radio astronomy is high. With satellite megaconstellations expanding and lunar exploration intensifying, the danger of tainting this pristine environment with anthropogenic radio noise becomes greater. If we lose the lunar far side to anthropogenic noise because we did not think ahead, it will preclude humanity from observing how the first structures in the universe formed for decades, cautioned Ronald Polidan, FarView lunar observatory concept principal investigator it will exclude humanity from seeing how the first structures in the universe were built for decades.
It is increasingly becoming necessary to have international cooperation. The Moon Farside Protection Permanent Committee is drafting guidelines to preserve the radio silence of the far side, calling for protected areas and technical standards like Faraday cages for lunar electronics. As Jack Burns noted, We just need to plan ahead. That’s what our IAA group is looking to do.
With LuSEE-Night imminent and bigger observatories on the horizon, the Moon’s far side is both a technological frontier and a scientific refuge providing, perhaps for the final time, a silent window into the universe’s oldest secrets.
