Radio astronomy is difficult on Earth. It's getting more difficult every day. Radio interference can be a problem because of our daily dependence on radio technology. For some wavelengths, even the Earth's atmosphere can be a problem. It absorbs or scatters radio light and makes it difficult for Earth-based telescopes to see these wavelengths clearly. Astronomers propose putting a radio telescope at the Moon's far side to overcome these problems.Proposed design for a radio telescope located in a lunar-crater. Credit: Saptarshi GangyopadhyayThe Moon is the perfect place to see the radio sky because it has no atmosphere that absorbs light. The radio signals from Earth are also blocked on the far side of Moon. We could build the most sensitive radio telescope in history if we built a radio dish inside a lunar crater. This is similar to how Arecibo was constructed in a natural valley. It would be sensitive enough to detect exoplanets.The majority of our knowledge about exoplanets is based on visible light. This occurs when an exoplanet passes directly in front of its star, usually from our vantage point. Infrared light can also make exoplanets bright, so we have seen many of the exoplanets directly in infrared. Sometimes, however, exoplanets can emit radio light. Jupiter is a good example. Its strong magnetic field and intense aurora make it very visible in radio. Large exoplanets, such as brown dwarfs, have enough aurora to make their radio glow from Earth.Simulation of aurora from an exoplanet Credit: Anthony SciolaExoplanets of Earth-sized size are unlikely to be bright enough in radio wavelengths for Earth to see, but they would likely be visible through a lunar radio telescope. The Astrophysical Journal recently published the answer to this question. The team studied the effects of a planet's magnetosphere on radio light it emits. This included the aurora that is produced during active periods of the planets stars.They discovered that visible aurora cluster near the magnetic poles of planets, but radio aurora are farther away and more scattered. Radio aurora can be seen on Earth but they are not visible because the Earth's ionosphere absorbs light. Any radio auroras from Earth-like exoplanets would be blocked by our ionosphere. A lunar observatory, however, would be able see radio aurora even if it is coming from the dark side.Based on simulations from this study, lunar radio observations could help determine the strength and stability the magnetosphere. This is especially important for exoplanets located in the potentially habitable zones of stars. Earth is a haven of life due to its rich atmosphere. This is due to its strong magnetosphere. We can learn whether the magnetospheres on exoplanets also have a rich atmosphere by studying them.NASA is currently investigating how to build a radio telescope for the Moon. We might finally see the aurora glow from a distant Earth if it is constructed in the next decades.Reference: Sciola Anthony et al. Numerical Simulations of Exoplanet Radioemission: Incorporating Inner Magnetosphere Current Driven Electron Acceleration. The Astrophysical Journal 94.1 (2021) 60.
