For radio astronomers, the far side of the Moon could be the last pristine haven in the solar system. The Earth and all man-made electromagnetic noise it emits into space will remain permanently below the horizon, allowing radio observatories stationed there to observe space freely without interference.
But the upcoming boom in lunar exploration could put that in jeopardy. Over the next decade or so, the Moon will become the target of hundreds of orbiters and landers, each of which can generate radio noise. Researchers expressed their concerns at a conference called “Astronomy from the Moon: The Next Decades” held at the Royal Society in London last month.
“This is probably the radio-quietest place in the solar system and we need to keep it,” said Mark Klein-Worth, an astronomer at Radboud University Nijmegen in the Netherlands.
“Is it still dark on the other side? You must be already nervous about what I’m asking,” said Joseph Lazio, a researcher at NASA’s Jet Propulsion Laboratory in Pasadena, California, at a conference. Told.
quiet zone
The far side of the Moon holds great potential in many fields, but it also holds unique potential in cosmology. Astronomers have mapped the sky using much of the electromagnetic spectrum, from microwaves to visible light to gamma rays. However, cosmic radio waves at frequencies below about 100 megahertz are very difficult to measure from Earth because of earth noise. Anything below 30 megahertz is completely off-limits. This is because the Earth’s atmosphere is absorbed by the ionosphere, the area where the universe meets. But these low frequencies hold a treasure trove of information about his first billion years or so of cosmic history.
The far side of the Moon is nearly ideal for exploring during these times, as it is shielded from Earth’s radio emissions, has little atmosphere, and lacks long, cold nights.
If all goes according to plan, a small U.S. lander called 2026 Lunar Electromagnetic Experiment (LuSee) Night will be the first dedicated space mission to take advantage of these conditions, designed with that goal in mind. It has been. (Chang’e 4, a historic Chinese mission that landed on the other side of the Earth in 2019, carried a simple radio astronomy antenna. However, the mission was not optimized for space observation. , the experiment was marred by radio frequency interference from the lander itself.)
With funding from both NASA and the U.S. Department of Energy, LuSee-Night will be transported to the other side by a private contractor as part of NASA’s early Commercial Lunar Payload Services program. Four 3-meter antennas arranged in a cross will attempt to measure the ‘cosmic dawn’. This is a feature thought to be detectable in the radio spectrum that reveals the appearance of the first stars in the universe.
noise limit
But even from the peaceful solitude of the far side of the moon, measuring LuSee’s cosmic dawn is difficult. The features of the early universe are 100,000 times weaker than the noise produced by galaxies in the same range of frequencies. It is important to limit noise from the spacecraft itself. “The only way is to turn off the lander completely,” says Stuart Bale, an astrophysicist at the University of California, Berkeley, who said the radio receiver had enough power to survive his two weeks of nights. to pack the battery. Principal Investigator on a NASA mission. Receiver electronics, including the clock that keeps the computer running, must be designed to “block” radiation to a limited portion of the spectrum, Bale says. It must work and have certified frequency stability.” Known and predictable noise sources are easier for the experimenter to filter out during data processing.
These are relatively simple precautions that all lunar missions, including commercial missions, can take, Bale says. If spacecraft are designed to suppress radio frequency interference, the potential for harm to future scientific experiments can be greatly reduced.
Melanie Johnston Hollitt, former director of the Murchison Widefield Array Radio Observatory in Western Australia, agrees. Massive Square Her Kilometers At Murchison, Australia her site of the Array Radio Telescope, she helped establish perhaps the world’s largest radio silence zone (over 500 kilometers).
A permit is required to bring electronic equipment onto the site, and “all equipment brought into the area goes through an additional electromagnetic testing process to check for unwanted radio emissions,” says Curtin University, Perth. says radio astronomer Johnston Hollitt. Australia. “I can confidently say that we can do that with CubeSats,” she says, referring to the tiny satellites that researchers fear will cluster around the Moon and create noise sources.
Still, “it’s incredibly difficult to suppress the interference to the levels needed to do accurate radio astronomy,” says Astronomy, who leads the Extraterrestrial Intelligence Project Breakthrough Listen at the University of California, Berkeley. author Andrew Siemion says. That work involves searching for signals across a wide range of radio waves, including the gigahertz frequencies that satellites communicate with.
economy of the moon
Astronomers face an uphill battle. The same technological advances that promise to make the Moon more accessible for experiments will also make the environment more crowded. There are more than 250 lunar missions planned over the next decade from the federal space agency and many private companies. In total, this amounts to his US$100 billion “moon economy,” according to Northern Sky Research, a Cambridge, Massachusetts consulting firm. There are also plans to install a lunar satellite navigation system, which can be a source of noise.
Alanna Krolikowski, a political scientist at the Missouri Institute of Science and Technology in Rolla, believes researchers should push for an international treaty to protect the moon. “There is a growing realization that governance is needed for this coming lunar renaissance,” she said at a conference last month.
The Artemis Accords, an international agreement led by NASA, seeks to provide guidance to ensure that agencies do not interfere with each other’s missions. However, it is primarily designed to serve the needs of signatories. A better way to regulate the moon could be to have rules drafted by the United Nations Commission on Peaceful Uses of Outer Space, Krolikowski said. “The window to do that is small and shrinking.”
This article is reproduced with permission and was first published on March 3, 2023.
