Scientists say a telescope on the Moon could advance physics — and they're hoping to build one

Humans are reliant on the Moon for far more than most realize. The natural satellite that lights up the nighttime sky moderates Earth's tilt, creating a more stable and livable climate for us here on Earth. Without the Moon, there would be no seasons. And, the Moon also creates tides, which help move heat across the ocean from the equator to the poles.

This article first appeared in Salon.

In addition to the Moon's vital effects on Earth, this enchanting orb that has mesmerized humans since history began could play a critical role in furthering our understanding of the early universe, if only we can build an observatory there.

Interestingly, there is now a plan in development to do just that. In April 2020, the National Aeronautics and Space Administration (NASA) awarded the Lunar Crater Radio Telescope (LCRT) project $500,000 for further research and development. The premise of this project is that a massive radio telescope would be built by robots on the far side of the Moon in a 100-meter long, bowl-shaped crater with the mission of observing radio wavelengths that are 10 meters and longer.

One might wonder: why the Moon? Isn't this something that we can do here on Earth? The truth is there is only so much data we can gather about the universe from Earth, in part due to the own limitations of our planet when it comes to observing the night sky. Earth's (comparatively) dense atmosphere, light pollution and man-made electromagnetic radiation significantly hamper our ability to clearly observe the cosmos from our home planet.

In the case of radio telescopes, the Moon is an especially tantalizing choice for an observatory. On Earth, scientists are unable to observe cosmic radio waves that are longer than 10 meters because of the ionosphere — a layer of electrons, charged atoms and molecules, that surrounds Earth and protects us from harmful rays from the sun and other bad stuff in space. Earth's ionosphere essentially absorbs any radio wavelengths over 10 meters long. On the Moon, a lack of atmosphere and radiation could (on the far side) vastly improve observations.

"Because the ionosphere is such a strong source, even [by] putting a satellite around it we won't be able to observe any of those wavelengths . . . it basically drowns out all the signals [over 10 meters]," said Saptarshi Bandyopadhyay, a Robotics Technologist at NASA Jet Propulsion Laboratory and a the lead researcher on the LCRT project, in an interview with Salon. "So we need to go to a place where we are shielded from Earth, and the best place to go to is the far side of the Moon.

An observatory on the far side of the Moon would have the added benefit of being perpetually shielded from electromagnetic noise from Earth. "The Moon is tidally locked, so only one side of the Moon faces us, and the other side of the Moon is always pointing away," Bandyopadhyay noted.

Bandyopadhyay argues there is an urgent need to better observe radio wavelengths over 10 meters, the kind that would have originated in the early days of our universe. Such a telescope might provide scientists with invaluable information about dark matter and dark energy.

These two substances mark one of the universe's most enduring mysteries. The existence of dark matter can be intuited by how it affects gravity, particularly the makeup and orbits of the largest-scale objects in the universe, galaxies. Yet no one knows exactly what dark matter it is, even though it makes up 27 percent of the universe's total mass and energy — far more than the 5 percent of the universe that "normal" matter, like planets and stars, comprises.

Dark energy, an ill-understood force that is responsible for the accelerating expansion of our universe, is estimated to comprise 68 percent of all matter and energy in the universe.

"Right now, we have some ideas, some models of what happened at the time of the Big Bang, and then we have some idea of what the current universe looks like, where all the galaxies are, how they're moving away, and things like that, but they're not many large questions in the middle [that remain unanswered]," Bandyopadhyay said. "A good part of that region is not observable because we have never looked at the universe 10 meters or longer, and that's what we want to observe — we want to observe those 10 meters and longer wavelengths, so that we can understand things like, 'why is there dark energy and dark matter, what is the pattern, and then why is there so much more matter and so little antimatter in the universe?'"

Bandyopadhyay said scientists need to find answers to these questions before humanity makes "another giant leap in physics."

Such a leap in understanding of fundamental physics might be nearer than one might think. Bandyopadhyay noted that 100 years ago, scientists were just starting to understand nuclear energy. Perhaps dark energy could be used in unknown ways in the future — we just have to understand it first.

"We know the universe is made out of only 4% matter, and 95% of the universe is dark matter and dark energy, and we understand nothing about it," Bandyopadhyay said. "My personal thought is if we could at least observe those regions of the universe, where dark energy and dark matter is active, we might be able to piece together what dark energy and dark matter is."

"Maybe our grandchildren would be able to take advantage of dark matter for interstellar travel," he mused.

Bandyopadhyay said the thought is a little "science fiction"; but argues in the 1920s, people likely would have thought powering homes from nuclear plants would have been science fictional, too.

Of course, to assemble such a device on the Moon would not be easy. In the LCRT proposal, robots would build the massive radio telescope. In order to work well, its dish would have to be at least like 10 times longer than the longest wavelength they'd observe. Bandyopadhyay said the budget would need to be between $1 billion and $5 billion. Two space crafts would be needed: one to deliver the mesh wire of the telescope, a material change to adapt to operating on the Moon, and a second to deliver the DuAxel rovers which would build the dish over several days or weeks.

"It's going to be a long journey," Bandyopadhyay said. "I would be very surprised if we managed to launch before I retired and I'm a very young scientist right now, but if you see all the other missions that's the kind of time it takes."

There is precedent for building a radio telescope in a crater: the Arecibo Observatory in Puerto Rico, which collapsed due to neglect recently, operated for decades and provided valuable scientific data. As with the proposed LCRT, the Arecibo Observatory took advantage of the natural concavity of its resident crater to focus distant radio waves. However, unlike the proposed lunar observatory, the Arecibo Observatory was not constructed entirely by robots.

Notably, only one spacecraft has successfully soft landed on the Moon's far side, which was China's Chang'e 4. Still, the very possibility of putting a radio telescope on the Moon is closer than it has ever been before. Such an instrument could pave the way for different types of telescopes, including optical ones, to make home in other spots on the Moon, ultimately transforming humanity's view of the cosmos.

"Visual telescopes would also benefit from the lack of an atmosphere on the Moon," said Avi Loeb, the former chair of the astronomy department at Harvard University (2011-2020). "Atmospheric turbulence blurs and distorts images of sources in the sky when observing from Earth; X-rays cannot propagate through the Earth's atmosphere and can also be observed from the Moon, and finally, the Moon has no geological activity and so a LIGO-like gravitational wave detector would benefit greatly from the lack of seismic noise and the vacuum that is offered for free — eliminating the need for vacuum tubes as used in the terrestrial version."