Everyone knows the Moon, but do you know how the Moon got to its position in the sky? Most don’t, which is why you can learn all about the Moon here!

Formation

The Moon’s formation is surrounded by mystery, as we are not sure exactly how the Moon formed. The several proposed scenarios include a proto-planet that is captured by the proto-Earth, a Moon that forms through splitting from a fast-spinning Earth, or the formation of the Earth and Moon system at the same time. Capturing a proto-planet requires too much energy to be dissipated to account for the size of the Moon. Separating the Moon from an Earth that rotates requires too much initial rotation for the Earth to be suitable.  And forming the Earth and Moon at the same time does not account for the difference in elemental composition between the two bodies.

The leading theory for how the Moon was formed is explained by a Mars-sized proto-planet, commonly called Theia, that smashed into the proto-Earth at just the right speed and angle to form the Moon as we know it today. After this collision, debris from both the proto-Earth and Theia system would have populated a region in Earth’s orbit, eventually coalescing the material to make the Moon much closer in orbit than it is today. Over billions of years, the friction caused by gravitational forces creating the tides slowed down the rotation of the Earth to our currently observed day, while simultaneously pushing the Moon back to its present-day position in the sky. Most of the questions that are unresolved from this scenario include specific elemental compositions of the Moon-Earth system, along with questions about the speed and angle of impact to create the Moon that we observe today.

Surface

The Moon is composed of mostly oxygen, followed by silicon, magnesium, iron, calcium, and aluminum. The surface has also been detected to have traces of ice, though nothing that would indicate large deposits of ice beneath the surface. After the formation of the Moon, the molten rock spread out around the surface, creating the smooth features we observe on the Moon today known as maria. The craters were caused by the so-called late heavy bombardment, which explains how many meteors crashed into the surface of the Moon creating the craters. Since the Moon does not have any weather system, the craters are preserved as they were originally created around 4 billion years ago.

Structure

The structure of the Moon follows a similar pattern to the Earth, without the heat required to generate a large-scale molten rock mantle. The crust is about 40 miles thick, with the rocky mantle comprising most of the Moon at 825 miles. The mantle is composed of predominantly iron and silicate material, contrasting with the dominant oxygen in the crust. There is believed to be a partially melted outer core that is composed of iron, surrounding the solid iron core that is only around 1% of the Moons mass at 420 miles in diameter.

Magnetic Field

Today the Moon has virtually no magnetic field, though a magnetic field is believed to have existed for around a billion years after the formation of the moon. While the Moon was young, the molten rock that was created in the collision of the proto-Earth and Theia system would have caused a magnetic field in the Moon like the one observed on Earth today. As the Moon slowly cooled down to obtain a solid mantle and core, the strong magnetic field dissipated to the extremely weak one we observe today.

Satellites

The Moon was an important goal during the height of the space race between the United States and the Soviet governments. The Soviet lead Luna missions successfully reached the Moon for the first time. Luna 1 was able to pass by the Moon, while Luna 2 intentionally crashed into the surface. Luna 3 was able to take the first photographs of the far side of the Moon. A soft landing was performed by Luna 9, while Luna 10 was the first satellite to orbit the Moon. For the United States, it wasn’t until Ranger 7 that the first pictures of the Moon were obtained, showing that craters were consistent across the entire surface of the Moon, even in the smooth maria.

The Lunar Orbiter program started by NASA was the first satellite to take pictures of the Earth from Lunar orbit. These pictures would eventually pave the way to select landing sites for the Apollo programs. Lunar Orbiter 1 took the first picture of Earth as a whole with Earth rising over the surface of the Moon. The first picture of the entire Earth was taken by Lunar Orbiter 5. By the end of the Lunar Orbiter missions, over 99% of the surface of the Moon had been mapped in high-resolution detail.

The Surveyor Program was a series of NASA missions in the 1960s, aiming to explore the lunar surface and prepare for the Apollo missions. With seven spacecraft, it successfully soft-landed on the Moon, providing crucial data for safe landings and identifying suitable Apollo landing sites. These missions advanced lunar geology understanding and greatly contributed to the success of the historic Apollo Moon landings, solidifying NASA's leadership in space exploration.

Hiten-Hagomoro, also known as Hiten Spacecraft, was a Japanese lunar probe launched in January 1990 by the Institute of Space and Astronautical Science (ISAS), now part of the Japan Aerospace Exploration Agency (JAXA). Its primary mission was to study the Moon's gravitational field and magnetic field. Hiten successfully demonstrated the use of lunar gravity assist to gain energy and transfer into a lunar orbit, making it Japan's first spacecraft to orbit the Moon.

The Clementine mission, a joint effort between NASA and the Ballistic Missile Defense Organization (BMDO), was launched in January 1994 with the primary objective of mapping the entire lunar surface and studying the Moon's geology, topography, and mineralogy. Equipped with advanced sensors and cameras, Clementine provided the first global multispectral images of the Moon, offering insights into its composition and surface features. Additionally, the mission tested new technologies, such as autonomous navigation and space communication techniques, which later became instrumental in future lunar and planetary missions.

The Lunar Prospector mission, launched in January 1998 by NASA, was a highly successful lunar exploration mission. Its primary objective was to study the Moon's composition, specifically searching for evidence of water ice at its poles. Lunar Prospector used neutron spectrometers to detect the presence of hydrogen, which could indicate the presence of water. The mission's findings provided compelling evidence of water ice in permanently shadowed regions near the lunar poles, revolutionizing our understanding of the Moon's resources and future human exploration possibilities. The Lunar Prospector mission concluded in July 1999 with an intentional crash into a polar crater, creating a plume that allowed scientists to analyze lunar materials and confirm the presence of water molecules.

SMART-1, Chang'e 1, and Chandrayaan-1 were all significant lunar missions conducted by different space agencies. SMART-1, launched by the European Space Agency (ESA) in 2004, used innovative ion propulsion to reach the Moon, studying its geology and mapping its surface composition. China's Chang'e 1, launched in 2007, marked China's first lunar mission, successfully orbiting the Moon and producing high-resolution lunar maps. Meanwhile, India's Chandrayaan-1, launched in 2008 by the Indian Space Research Organisation (ISRO), carried out detailed mapping of the lunar surface, discovered water molecules on the Moon, and detected evidence of volcanic activity.

The Lunar Reconnaissance Orbiter (LRO) is a NASA spacecraft launched in June 2009 to conduct comprehensive lunar exploration. Equipped with advanced instruments, LRO's primary mission is to map the Moon's surface, gather data on its topography, temperature, and radiation environment. It has provided high-resolution images of potential landing sites for future missions, including the Apollo landing sites, and has helped identify regions with potential resources for future human exploration. Additionally, LRO's continuous observations have enhanced our understanding of the Moon's geology, contributing to scientific research and our preparations for future lunar missions.

Chang'e 3, launched by China in December 2013, was a groundbreaking lunar mission that successfully achieved China's first soft landing on the Moon. It carried the Yutu rover, which explored the lunar surface and conducted various scientific experiments. Chang'e 4, launched in December 2018, was the first mission to land on the far side of the Moon, where it deployed the Yutu-2 rover, continuing China's lunar exploration with innovative experiments. Chang'e 5, launched in November 2020, was a historic mission that brought back lunar samples to Earth, marking the first time since the 1970s that material from the Moon was returned to our planet for analysis.

Human Missions

The Mercury space missions conducted by NASA were instrumental in paving the way for landing humans on the Moon during the Apollo program. Launched in the late 1950s and early 1960s, the Mercury program aimed to send the first American astronauts into space. These missions provided invaluable experience in human spaceflight, essential for understanding the challenges of space travel and ensuring the safety of astronauts during extended missions. The knowledge gained from Mercury, such as re-entry and recovery procedures, spacecraft design, and orbital mechanics, formed the foundation for subsequent crewed space missions, including the historic Apollo Moon landings.

The Gemini space missions conducted by NASA played a pivotal role in the successful landing of humans on the Moon during the Apollo program. Launched in the mid-1960s, the Gemini program aimed to develop and test crucial spaceflight techniques and technologies for future crewed missions. These missions enabled NASA to gain valuable experience in long-duration flights, rendezvous and docking maneuvers, extra-vehicular activities (spacewalks), and orbital maneuvering. The knowledge and skills acquired during the Gemini program were essential in overcoming the technical challenges of lunar travel, spacecraft navigation, and life support systems, thus significantly contributing to the success of the Apollo missions.

The Apollo missions before Apollo 11 were of utmost significance as they laid the groundwork for the monumental achievement of landing humans on the Moon. Launched by NASA in the 1960s, the Apollo program consisted of several crewed missions, each building upon the knowledge and experience gained from the previous ones. Apollo 1, although tragic, provided crucial lessons in safety protocols and spacecraft design. Apollo 7 tested the Command Module's functionality in Earth's orbit, validating its reliability for future missions. Apollo 8 marked the first human journey to the Moon, orbiting its surface and inspiring a global audience. Apollo 9 and 10 further tested critical lunar modules and docking procedures. Apollo 11's success in 1969, with astronauts Neil Armstrong and Buzz Aldrin becoming the first humans to set foot on the lunar surface, was a culmination of years of perseverance, technical expertise, and collective effort from the earlier Apollo missions. The successful execution of these missions, along with their trial and error process, provided the vital knowledge, experience, and confidence needed to achieve the ultimate goal of landing humans on the Moon and safely bringing them back to Earth.

After the historic success of Apollo 11, the subsequent Apollo missions continued to push the boundaries of human exploration and scientific discovery. Apollo 12, launched in November 1969, precisely landed near the Surveyor 3 spacecraft, allowing astronauts to retrieve its hardware for analysis back on Earth. Apollo 13, while facing a life-threatening in-space emergency, demonstrated the ingenuity and resourcefulness of the NASA team, safely returning the crew home. Apollo 14 and 15 extended lunar exploration, conducting extensive scientific experiments and deploying lunar rovers for greater mobility. Apollo 16 and 17 continued to enhance our understanding of the Moon's geology and collected a wealth of lunar samples. Each mission played a crucial role in advancing our knowledge of space and our ability to live and work in the challenging environment beyond Earth.