The far side of the moon could offer a very deep view of the universe

With NASA’s Artemis 1 mission launching to the Moon this month, Space.com takes a look at what we know about the Moon and why we care. Join us for our special report on Moon Week in Artemis Countdown 1.

The scientific potential of future lunar missions extends well beyond the moon.

A new radio telescope on the other side of the moon could capitalize on the new Artemis the age of lunar exploration, say scientists who hope to one day use such a telescope to probe deeper into the universe than even the new James Webb Space Telescope box.

“The argument for placing a radio telescope on the far side of the moon is to look at lower radio frequencies that are otherwise heavily polluted by human radio transmissions on Earth,” said Stanford University physicist Steven Kahn. in California, at Space.com. .

Related: As NASA nears return to the Moon with the Artemis program, excitement among lunar scientists reaches fever pitch

Kahn led one of the panels of the recent 10-year survey in astronomy and astrophysics (Pathways to Discovery in Astronomy and Astrophysics for the 2020s), focusing on electromagnetic observations from space. A proposal for a lunar telescope named OTHER SIDE, led by Jack Burns of the University of Colorado at Boulder, has been touted as a potential “probe-class” mission costing between $1 billion and $2 billion. Burns had been working on a plan for a radio telescope on the moon since the 1980s, but ultimately FARSIDE was not selected for recommendation by the Decade Survey.

However, a brand new concept is currently being evaluated, called the Lunar Crater Radio Telescope, which is being led by Saptarshi Bandyopadhyay of NASA’s Jet Propulsion Laboratory in California.

“We want to build a 350-meter-diameter radio telescope in a 1.3-kilometer-wide crater on the far side of the moon,” Bandyopadhyay, who is a robotics technologist, told Space.com. (That would be a 1,150-foot-wide flat in a 0.8-mile crater.)

The original plan called for an even larger telescope, 0.6 miles (1 km) in size, but the sheer scale of this instrument proved unfeasible due to the sheer mass that would have to be launched from Earth. . Fortunately, “As we looked at the science, we realized that a diameter of 350 meters would be enough to give us the science we want to get,” Bandyopadhyay said.

This science consists of going back in time to a distant era known as the era of reionization. Shortly after the big Bang there were no stars or galaxies, only a vast fog of neutral hydrogen. This period has been dubbed the “Cosmic Dark Age“Eventually, the hydrogen began to fuse together to form stars and galaxies, illuminating the universe and ionizing the neutral hydrogen. It is this first era that the Lunar Crater Radio Telescope hopes to see.

Ordinarily, neutral hydrogen emits radio waves at a wavelength of 8.3 inches (21 centimeters), but cosmic expansion will have lengthened the wavelength of radio waves emitted by hydrogen at the age darkness at extremely long wavelengths of tens of meters.

It is difficult to detect this long-wavelength light on Earth, in part because the ionosphere (the upper realm of our atmosphere) can reflect light of these wavelengths back into space, and in part because terrestrial radio interference can obscure it. The thing to do would be to build a giant radio telescope on the far side of the moon, where there is no ionosphere, and where the moon itself can shield the telescope from interference from Earth.

“The recent Astrophysical Decadal Survey talked about the need to understand what the Dark Ages looked like, and that to do this kind of work, a single-receiver global measurement is needed,” Bandyopadhyay said. “That’s exactly what we offer.”

Bandyopadhyay’s plan is to send a spacecraft into a suitable crater on the far side of the moon. The spacecraft would land inside the crater and then pull several cables with anchors into the rim of the crater, where the anchors would safely enter the lunar regolith. The cables would then be taut, creating a frame to hold the wire-mesh radio dish, which would be bent like origami in the lander and opened when the cables were taut. A feed antenna would be deployed above the dish and a spacecraft above would first provide a beacon signal to help calibrate the telescope and then act as a relay for data and commands, as Earth cannot be seen from the other lunar side, hidden as it is behind the body of the moon.

At least, that’s the plan. The Lunar Crater radio telescope is currently in Phase II of NASA’s Innovative Advanced Concepts (NIAC) development program, through which it received $500,000 in funding to mature the necessary technology. But that’s a far cry from the multi-billion dollar budget that would be needed to make the telescope’s mission a success.

Due to its high price, the telescope needs strong support from the scientific community to get a recommendation in the next 10-year survey.

“What we need to do now is make a very strong argument why this should be done,” Bandyopadhyay said. “So hopefully when the next 10-year survey comes around, we’ll have put enough time and effort into it for them to recommend the mission.”

However, the same issues that worked against FARSIDE could also work against the Lunar Crater radio telescope, in particular that while it will do important science, it’s also too specialized, Kahn said.

“Given its limited purpose, it’s going to be difficult to prioritize this and rank it number one. [in the next decadal survey in 2030],” he said.

However, there may be another option, suggested Kahn (who is not directly involved in the project), in that it fits with NASA’s desire to do more exploration on the moon. “There are programmatic reasons for wanting to do more frequent flights to the Moon, and so the hope is to try to capitalize on that,” he said.

This approach is embodied by NASA Lunar Payload Commercial Services (CLPS), which will see more than 50 small science payloads delivered to the Moon by private contractors over the next three years. Three of these payloads will head for the 194-mile-wide (312 km) Schrödinger crater, which is an impact basin on the far side of the moon near the lunar south pole, in 2025 on a lunar lander built by the Massachusetts-based aerospace company Drape.

“From a scientific perspective, the far side of the moon is one of the main places we want to get information from,” Debra Needham, a planetary scientist at NASA’s Marshall Space Flight Center in Huntsville, Alabama, told Space.com.

Schrödinger is an interesting target, and it is thought to be the second youngest impact basin on the moon. The three payloads, named Farside Seismic Suite (FSS), Lunar Interior Temperature and Materials Suite (LITMS) and Lunar Surface ElectroMagnetics Experiment (LuSEE), will study the relationship between formation and crater size, as well as the interior structure of the moon.

“The impact that formed Schrödinger was so large that we think it penetrated through the moon’s upper crust and into the mantle,” Needham said. “Exploring that will be really important in helping us understand the overall chemistry of the moon, what the moon is made of inside and out, and how that helps us understand how the moon formed and how it’s been cooling since its early hottest days when it was volcanically active and a much more dynamic place than it is today.”

For example, seismometers will listen moon quakes caused by meteor impacts or pressure on the moon’s interior caused by gravitational tides emanating from Earth. As seismic tremors reverberate through the moon’s interior, the signal that the FSS will detect can tell scientists about the structure, composition, and density of the moon’s interior.

Meanwhile, the LITMS experiment is armed with a heat flux probe with which it will be able to take the moon’s internal temperature for more details on the moon’s interior.

“The thermal probe measurements during Apollo were made in an anonymously hot region of the moon,” Needham said. “There is a chemical anomaly on the near side that is giving off heat, so LITMS will be the first time we get measurements outside of that area.”

The final experiment, LuSEE, will study dust in the moon’s exosphere, which is the thin layer of gas and dust that clings near the surface and is thrown off the ground by micrometeorite impacts and electrostatic forces. .

Together, this trio of small robotic experiments could pave the way for deeper exploration of the far side. Such exploration would follow the tracks (or should they be wheel tracks?) Yutu 2 roverwhich became the first spacecraft to land on the other side when it landed on January 3, 2019in a crater called Von Kármán.

NASA’s Artemis 1 mission to the moon will launch Monday, Aug. 29, during a two-hour window that opens at 8:33 a.m. EDT (12:33 p.m. GMT). You can watch the launch coverage live courtesy of NASA and follow Space.com Live Updates on the mission.

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