Explainer: The Importance of Analyzing Samples from the Moon's Far Side
Explainer: The Importance of Analyzing Samples from the Moon's Far Side
TroibNews 
**Editor's note:** Lunar samples gathered by China's Chang'e-6 mission from the moon's far side will be showcased at the 15th China International Aviation and Aerospace Exhibition, also referred to as Airshow China, this November. Wang Zhaokui, a professor at Tsinghua University's School of Aerospace Engineering and head of the Department of Aeronautics and Astronautics Engineering, discusses the technological advancements that made the Chang'e-6 mission possible and the significance of this pioneering sampling mission to the moon's far side. The views expressed in this article are those of the author and do not necessarily represent those of CN.
**Why is the far side of the moon so mysterious?**
The far side of the moon remains elusive to observers on Earth because the moon is "tidally locked," ensuring that only one side is visible from our planet at all times. This phenomenon is attributed to the gradual loss of the moon's rotational energy over billions of years due to magnetic interactions with Earth’s oceans.
The first images of the moon's far side were not captured until 1959 when the Soviet Luna 3 spacecraft provided a glimpse of its rugged terrain, marked by numerous craters and fewer dark basaltic plains, known as maria.
In 2019, China’s Chang'e-4 made history by becoming the first spacecraft to land on and explore the remote region of the moon. Just recently, in late June of this year, Chang'e-6 returned with valuable samples weighing 1,935.3 grams from the moon's far side.
The exploration of this area has been slower due to the challenges posed by the moon's physical barrier, which complicates direct communication with spacecraft, landers, and rovers.
To overcome this obstacle, China has implemented technologies that facilitate communication around the moon’s curvature, allowing for effective contact with its far side.
**What new technologies have made the Chang'e-6 mission possible?**
A significant innovation that has enabled real-time communication with the far side is the deployment of the Queqiao relay satellite, a complex undertaking in itself. A key challenge of the Queqiao satellite is positioning it in a stable halo orbit around the Earth-Moon L2 Lagrangian point.
Lagrangian points are special locations in space where the gravitational forces of two large bodies balance with the centripetal force acting on a smaller object. At these points, a satellite can theoretically maintain a stable position relative to Earth and the moon.
This advantageous positioning has allowed Queqiao to function as a communication link, continuously relaying signals to and from Earth, which is critical for the timely data transfer and decision-making essential for successful lunar operations.
However, the L2 point poses specific challenges, as it is dynamically unstable. Small deviations from this point require corrective maneuvers to keep the satellite in the intended orbit. Such deviations, caused by solar pressure and various perturbative forces, necessitate careful management, though it remains stable enough for the satellite to remain nearby with minimal corrections.
Essentially, Queqiao was engineered to execute complex maneuvers to maintain its position amidst the delicate balance of forces at play. Another groundbreaking method is the "half-ballistic jump re-entry," or "stone skipping" technique, which ensures safe re-entry of spacecraft returning to Earth.
This technique utilizes the Earth's atmospheric drag to slow down the spacecraft. Upon the initial contact with the atmosphere, the spacecraft uses this drag to decelerate and "bounce" back into space temporarily.
After this brief re-ascension, the spacecraft re-enters the atmosphere at a lower speed and thermal load, allowing for a secure landing. Both Chang'e-5 and Chang'e-6 have utilized this approach, akin to throwing a stone across water to make it skip along the surface.
**What could we learn from the materials brought back?**
Lunar rocks hold a treasure trove of information. Scientists are particularly keen on studying samples from the South Pole-Aitken Basin, which might provide insights into the "late heavy bombardment theory."
Identified as one of the oldest and largest impact craters in the solar system, the South Pole-Aitken Basin dates back around 4.6 billion years, shortly after the formation of the Solar System. This crater is believed to have formed during a period when leftover planetesimals frequently collided with emerging planets.
This epoch of intense impacts is thought to have been so extreme that it may have stripped enough material from Earth to contribute to the moon's formation. By approximately 3.8 billion years ago, some scientists suggest that the rate of such impacts decreased to a level comparable to what we observe today.
This theory has influenced our understanding of when life began on Earth, as it was previously thought that all water had vaporized during this early period, rendering the planet uninhabitable. However, emerging evidence from meteorites and new findings from space missions have prompted experts to reevaluate this theory.
Clarifying this issue could significantly impact vital questions regarding the origins of life and the conditions on early Earth, potentially revealing many intriguing and important insights.
For example, recent discoveries hint at the possibility of water and other volatile substances existing on the moon, which could enhance future lunar exploration and potential colonization efforts. Studying lunar samples could clarify the presence, distribution, and origins of these substances.
**Could manned missions be next?**
China is actively planning to send astronauts to land on the moon before 2030, although there are currently no specific plans for a manned mission to the moon's far side. Tsinghua University has engaged in numerous research projects related to manned lunar missions and aims to contribute to future endeavors in space exploration.
**What extra challenges might an astronaut face on the far side of the moon?**
An astronaut operating on the far side of the moon would encounter several distinct and formidable challenges. One significant issue is the terrain’s ruggedness and the prevalence of craters compared to the "relatively smooth" near side.
Successfully navigating this challenging landscape would require advanced autonomous systems as well as extensive training for the astronauts. Moreover, the isolation caused by communication delays while sending signals around the moon could result in considerable psychological stress. Astronauts undertaking this mission would need resilience and highly effective support systems to cope with these unique stresses.
**What's next for the moon mission?**
The moon, being the closest celestial body to Earth, has a communication delay of fewer than two seconds on its near side, making it an ideal first step for deeper space exploration.
Before embarking on missions to more distant destinations like Mars, mastering lunar exploration and operations is essential. This foundational step to the moon's far side will allow for the development of crucial technologies and strategies for longer missions.
Given that over 50 years have passed since the Apollo moon landings, the next chapter of lunar exploration aims to go beyond mere visitation.
Upcoming missions are expected to focus on establishing functional lunar bases. These bases could support lunar mining operations and enable the use of in-situ resources, fostering a more sustainable approach to space operations. Such developments would position the moon as a vital "stepping stone" for further exploration of other celestial bodies.
Mark B Thomas for TROIB News
**Why is the far side of the moon so mysterious?**
The far side of the moon remains elusive to observers on Earth because the moon is "tidally locked," ensuring that only one side is visible from our planet at all times. This phenomenon is attributed to the gradual loss of the moon's rotational energy over billions of years due to magnetic interactions with Earth’s oceans.
The first images of the moon's far side were not captured until 1959 when the Soviet Luna 3 spacecraft provided a glimpse of its rugged terrain, marked by numerous craters and fewer dark basaltic plains, known as maria.
In 2019, China’s Chang'e-4 made history by becoming the first spacecraft to land on and explore the remote region of the moon. Just recently, in late June of this year, Chang'e-6 returned with valuable samples weighing 1,935.3 grams from the moon's far side.
The exploration of this area has been slower due to the challenges posed by the moon's physical barrier, which complicates direct communication with spacecraft, landers, and rovers.
To overcome this obstacle, China has implemented technologies that facilitate communication around the moon’s curvature, allowing for effective contact with its far side.
**What new technologies have made the Chang'e-6 mission possible?**
A significant innovation that has enabled real-time communication with the far side is the deployment of the Queqiao relay satellite, a complex undertaking in itself. A key challenge of the Queqiao satellite is positioning it in a stable halo orbit around the Earth-Moon L2 Lagrangian point.
Lagrangian points are special locations in space where the gravitational forces of two large bodies balance with the centripetal force acting on a smaller object. At these points, a satellite can theoretically maintain a stable position relative to Earth and the moon.
This advantageous positioning has allowed Queqiao to function as a communication link, continuously relaying signals to and from Earth, which is critical for the timely data transfer and decision-making essential for successful lunar operations.
However, the L2 point poses specific challenges, as it is dynamically unstable. Small deviations from this point require corrective maneuvers to keep the satellite in the intended orbit. Such deviations, caused by solar pressure and various perturbative forces, necessitate careful management, though it remains stable enough for the satellite to remain nearby with minimal corrections.
Essentially, Queqiao was engineered to execute complex maneuvers to maintain its position amidst the delicate balance of forces at play. Another groundbreaking method is the "half-ballistic jump re-entry," or "stone skipping" technique, which ensures safe re-entry of spacecraft returning to Earth.
This technique utilizes the Earth's atmospheric drag to slow down the spacecraft. Upon the initial contact with the atmosphere, the spacecraft uses this drag to decelerate and "bounce" back into space temporarily.
After this brief re-ascension, the spacecraft re-enters the atmosphere at a lower speed and thermal load, allowing for a secure landing. Both Chang'e-5 and Chang'e-6 have utilized this approach, akin to throwing a stone across water to make it skip along the surface.
**What could we learn from the materials brought back?**
Lunar rocks hold a treasure trove of information. Scientists are particularly keen on studying samples from the South Pole-Aitken Basin, which might provide insights into the "late heavy bombardment theory."
Identified as one of the oldest and largest impact craters in the solar system, the South Pole-Aitken Basin dates back around 4.6 billion years, shortly after the formation of the Solar System. This crater is believed to have formed during a period when leftover planetesimals frequently collided with emerging planets.
This epoch of intense impacts is thought to have been so extreme that it may have stripped enough material from Earth to contribute to the moon's formation. By approximately 3.8 billion years ago, some scientists suggest that the rate of such impacts decreased to a level comparable to what we observe today.
This theory has influenced our understanding of when life began on Earth, as it was previously thought that all water had vaporized during this early period, rendering the planet uninhabitable. However, emerging evidence from meteorites and new findings from space missions have prompted experts to reevaluate this theory.
Clarifying this issue could significantly impact vital questions regarding the origins of life and the conditions on early Earth, potentially revealing many intriguing and important insights.
For example, recent discoveries hint at the possibility of water and other volatile substances existing on the moon, which could enhance future lunar exploration and potential colonization efforts. Studying lunar samples could clarify the presence, distribution, and origins of these substances.
**Could manned missions be next?**
China is actively planning to send astronauts to land on the moon before 2030, although there are currently no specific plans for a manned mission to the moon's far side. Tsinghua University has engaged in numerous research projects related to manned lunar missions and aims to contribute to future endeavors in space exploration.
**What extra challenges might an astronaut face on the far side of the moon?**
An astronaut operating on the far side of the moon would encounter several distinct and formidable challenges. One significant issue is the terrain’s ruggedness and the prevalence of craters compared to the "relatively smooth" near side.
Successfully navigating this challenging landscape would require advanced autonomous systems as well as extensive training for the astronauts. Moreover, the isolation caused by communication delays while sending signals around the moon could result in considerable psychological stress. Astronauts undertaking this mission would need resilience and highly effective support systems to cope with these unique stresses.
**What's next for the moon mission?**
The moon, being the closest celestial body to Earth, has a communication delay of fewer than two seconds on its near side, making it an ideal first step for deeper space exploration.
Before embarking on missions to more distant destinations like Mars, mastering lunar exploration and operations is essential. This foundational step to the moon's far side will allow for the development of crucial technologies and strategies for longer missions.
Given that over 50 years have passed since the Apollo moon landings, the next chapter of lunar exploration aims to go beyond mere visitation.
Upcoming missions are expected to focus on establishing functional lunar bases. These bases could support lunar mining operations and enable the use of in-situ resources, fostering a more sustainable approach to space operations. Such developments would position the moon as a vital "stepping stone" for further exploration of other celestial bodies.
Mark B Thomas for TROIB News
