7.1: Exploration

Humans began exploring the Moon when they started studying the Moon instead of just noticing it's presence in the sky.  This could have involved tracking how the Moon moved across the sky during a single night, or how it changed shape from day to day.  These kind of observations could easily be made with the human eye.

This chapter will demonstrate how new technology made it possible for people to understand new things about the Moon. The next section is about when humans started using telescopes to study the Moon and how it changed our understanding of our nearest neighbor. 

Observations from Earth

 

If you look at the Moon through a telescope, you can see that it is covered by impact craters of all sizes. The most conspicuous of the Moon’s surface features—those that can be seen with the unaided eye and that make up the feature often called “the man in the Moon”—are vast splotches of darker lava flows.

Thousands of individual craters have been named, however, mostly for great scientists and philosophers (Figure 9.6). Among the most prominent craters are those named for Plato, Copernicus, Tycho, and Kepler. Galileo only has a small crater, however, reflecting his low standing among the Vatican scientists who made some of the first lunar maps.

Combine images into one box and Caption?

Figure \(\PageIndex{1}\): Thomas Harriot drew this map of the Moon sometime between 1610 and 1613, based on multiple observations with a telescope starting in July of 1609.  (Lunar Map by Thomas Harriot, Public domain, via Wikimedia Commons)

 

Figure \(\PageIndex{1}\): Galileo Galilei drew these sketches of the Moon with the help of a telescope starting in November of 1609. They were published in his book, Sidereus nuncius.  (Drawings of the Moon by Galileo Galilei, CC BY 4.0, via Wikimedia Commons)

 

Before the 1600s, European astronomers believed the Moon was perfectly spherical, smooth, and unblemished, even though people could see spots on the surface using their eyes.  As far as we know, Thomas Harriot was the first person to point a telescope at the Moon and sketch what he saw during observations in July of 1609.  He eventually combined his sketches into a map shown in Figure ??, which was not published until the 20th century. Galileo Galilei began his observations in November of 1609, eventually publishing his work in the book Sidereus nuncius, or Starry Messenger, Figure ???.

Describe differences between sketches, Galileo showed light and shadows - Moon can't be smooth

Insert assignment:  Why are these images different?

Maria

Centuries ago, early lunar observers thought that the Moon had continents and oceans and that it was a possible abode of life. They called the dark areas “seas” (maria in Latin, or mare in the singular, pronounced “mah ray”). Their names, Mare Nubium (Sea of Clouds), Mare Tranquillitatis (Sea of Tranquility), and so on, are still in use today. In contrast, the “land” areas between the seas are not named.

1. Start with image of near side of the Moon
2. What is the most conspicuous feature Man on the Moon
3. find multiple interpretations of the Man in the Moon - DEI
4. What do you see?
5. mare definition - edit Openstax (below)
6. lava flows?  mention lava flows here? or wait?
7. sinuous rilles - could people see them?  did they think they were rivers?
8. summarize early 20th century ground based observations - understanding before space age

Notes

3km lower than highlands 

•  

• Maria (MAH ree uh) latin for seas, single mare (MAHR- ray)– smooth dark planes – early observers thought they were lakes, or oceans but have ridges, faults, & craters 

• Lava flows but no volcanoes 

• A few small lava domes - wait until later - when did we know???

• Sinuous rilles – collapsed lava tubes

The most conspicuous of the Moon’s surface features—those that can be seen with the unaided eye and that make up the feature often called “the man in the Moon”—are vast splotches of darker lava flows.

Centuries ago, early lunar observers thought that the Moon had continents and oceans and that it was a possible abode of life. They called the dark areas “seas” (maria in Latin, or mare in the singular, pronounced “mah ray”). Their names, Mare Nubium (Sea of Clouds), Mare Tranquillitatis (Sea of Tranquility), and so on, are still in use today. In contrast, the “land” areas between the seas are not named. Thousands of individual craters have been named, however, mostly for great scientists and philosophers (Figure 9.6). Among the most prominent craters are those named for Plato, Copernicus, Tycho, and Kepler. Galileo only has a small crater, however, reflecting his low standing among the Vatican scientists who made some of the first lunar maps.

The maria are much less cratered than the highlands, and cover just 17% of the lunar surface, mostly on the side of the Moon that faces Earth (Figure 9.9).

Craters

1. start with zoom in on craters in image of near side of Moon
2. what did craters look like to observers?  could they tell that they were bowl shaped?  light and shadow?
3. what is a crater?  get into history?  
4. volcanic vs impact craters
5.  

• •  

Mountains

1. Get images of mountains or focus on mountains in sketches???
2. summarize what people saw
3. review mountain formation on Earth, some are volcanoes, some are from plate tectonics, or other tectonic events
4. turns out they were crater rims and central peaks?   

Atmosphere

Astronomers have know that the Moon does not have an atmosphere similar to the Earth's for a long time.  Event without a telescope, any person could see that the Moon had no clouds.  Astronomers using telescopes could see that the terminator, the boundary between the lit and unlit areas of the Moon was a very sharp line. When light passes through an atmosphere, it is scattered - instead of the photons all traveling parallel in straight lines from the Sun, their paths are randomly changed, causing them to spread out. Since sunlight is scattered by the Earth's atmosphere, someone observing a sunrise on Earth does not see a sharp, bright line traveling across the ground. Instead they see a gradual brightening. 

evidence

1. no change in light when star transits - no interference from an atmosphere
2. terminator (edge of light from Sun) has sharp edge - no scattering from atmosphere

conclusion

no atmosphere

The Moon has only one-eightieth the mass of Earth and about one-sixth Earth’s surface gravity—too low to retain an atmosphere (Figure 9.2). Moving molecules of a gas can escape from a planet just the way a rocket does, and the lower the gravity, the easier it is for the gas to leak away into space. While the Moon can acquire a temporary atmosphere from impacting comets, this atmosphere is quickly lost by freezing onto the surface or by escape to surrounding space.

Observe the Moon

The Moon is one of the most beautiful sights in the sky, and it is the only object close enough to reveal its topography (surface features such as mountains and valleys) without a visit from a spacecraft. A fairly small amateur telescope easily shows craters and mountains on the Moon as small as a few kilometers across.

Even as seen through a good pair of binoculars, we can observe that the appearance of the Moon’s surface changes dramatically with its phase. At full phase, it shows almost no topographic detail, and you must look closely to see more than a few craters. This is because sunlight illuminates the surface straight on, and in this flat lighting, no shadows are cast. Much more revealing is the view near first or third quarter, when sunlight streams in from the side, causing topographic features to cast sharp shadows. It is almost always more rewarding to study a planetary surface under such oblique lighting, when the maximum information about surface relief can be obtained.

The flat lighting at full phase does, however, accentuate brightness contrasts on the Moon, such as those between the maria and highlands. Notice in Figure 9.16 that several of the large mare craters seem to be surrounded by white material and that the light streaks or rays that can stretch for hundreds of kilometers across the surface are clearly visible. These lighter features are ejecta, splashed out from the crater-forming impact.

Figure 9.16 : Appearance of the Moon at Different Phases. (a) Illumination from the side brings craters and other topographic features into sharp relief, as seen on the far left side. (b) At full phase, there are no shadows, and it is more difficult to see such features. However, the flat lighting at full phase brings out some surface features, such as the bright rays of ejecta that stretch out from a few large young craters. (credit: modification of work by Luc Viatour)

By the way, there is no danger in looking at the Moon with binoculars or telescopes. The reflected sunlight is never bright enough to harm your eyes. In fact, the sunlit surface of the Moon has about the same brightness as a sunlit landscape of dark rock on Earth. Although the Moon looks bright in the night sky, its surface is, on average, much less reflective than Earth’s, with its atmosphere and white clouds. This difference is nicely illustrated by the photo of the Moon passing in front of Earth taken from the Deep Space Climate Observatory spacecraft (Figure 9.17). Since the spacecraft took the image from a position inside the orbit of Earth, we see both objects fully illuminated (full Moon and full Earth). By the way, you cannot see much detail on the Moon because the exposure has been set to give a bright image of Earth, not the Moon.

Figure 9.17 : The Moon Crossing the Face of Earth. In this 2015 image from the Deep Space Climate Observatory spacecraft, both objects are fully illuminated, but the Moon looks darker because it has a much lower average reflectivity than Earth. (credit: modification of work by NASA, DSCOVR EPIC team)

Spacecraft

Exploration of the Moon

Most of what we know about the Moon today derives from the US Apollo program, which sent nine piloted spacecraft to our satellite between 1968 and 1972, landing 12 astronauts on its surface (Figure 9.1). Before the era of spacecraft studies, astronomers had mapped the side of the Moon that faces Earth with telescopic resolution of about 1 kilometer, but lunar geology hardly existed as a scientific subject. All that changed beginning in the early 1960s. Initially, Russia took the lead in lunar exploration with Luna 3, which returned the first photos of the lunar far side in 1959, and then with Luna 9, which landed on the surface in 1966 and transmitted pictures and other data to Earth. However, these efforts were overshadowed on July 20, 1969, when the first American astronaut set foot on the Moon.

Table 9.2 summarizes the nine Apollo flights: six that landed and three others that circled the Moon but did not land. The initial landings were on flat plains selected for safety reasons. But with increasing experience and confidence, NASA targeted the last three missions to more geologically interesting locales. The level of scientific exploration also increased with each mission, as the astronauts spent longer times on the Moon and carried more elaborate equipment. Finally, on the last Apollo landing, NASA included one scientist, geologist Jack Schmitt, among the astronauts (Figure 9.3).

Table 9.2: Apollo Flights to the Moon

Flight	Date	Landing Site	Main Accomplishment
Apollo 8	Dec. 1968	—	First humans to fly around the Moon
Apollo 10	May 1969	—	First spacecraft rendezvous in lunar orbit
Apollo 11	July 1969	Mare Tranquillitatis	First human landing on the Moon; 22 kilograms of samples returned
Apollo 12	Nov. 1969	Oceanus Procellarum	First Apollo Lunar Surface Experiment Package (ALSEP); visit to Surveyor 3 lander
Apollo 13	Apr. 1970	—	Landing aborted due to explosion in service module
Apollo 14	Jan. 1971	Mare Nubium	First “rickshaw” on the Moon
Apollo 15	July 1971	Mare Imbrium/Hadley	First “rover;” visit to Hadley Rille; astronauts traveled 24 kilometers
Apollo 16	Apr. 1972	Descartes	First landing in highlands; 95 kilograms of samples returned
Apollo 17	Dec. 1972	Taurus-Littrow highlands	Geologist among the crew; 111 kilograms of samples returned

Figure 9.3 : Scientist on the Moon. Geologist (and later US senator) Harrison “Jack” Schmitt in front of a large boulder in the Littrow Valley at the edge of the lunar highlands. Note how black the sky is on the airless Moon. No stars are visible because the surface is brightly lit by the Sun, and the exposure therefore is not long enough to reveal stars.

In addition to landing on the lunar surface and studying it at close range, the Apollo missions accomplished three objectives of major importance for lunar science. First, the astronauts collected nearly 400 kilograms of samples for detailed laboratory analysis on Earth (Figure 9.4). These samples have revealed as much about the Moon and its history as all other lunar studies combined. Second, each Apollo landing after the first one deployed an Apollo Lunar Surface Experiment Package (ALSEP), which continued to operate for years after the astronauts departed. Third, the orbiting Apollo command modules carried a wide range of instruments to photograph and analyze the lunar surface from above.

Figure 9.4 : Handling Moon Rocks. Lunar samples collected in the Apollo Project are analyzed and stored in NASA facilities at the Johnson Space Center in Houston, Texas. Here, a technician examines a rock sample using gloves in a sealed environment to avoid contaminating the sample. (credit: NASA JSC)

The last human left the Moon in December 1972, just a little more than three years after Neil Armstrong took his “giant leap for mankind.” The program of lunar exploration was cut off midstride due to political and economic pressures. It had cost just about $100 per American, spread over 10 years—the equivalent of one large pizza per person per year. Yet for many people, the Moon landings were one of the central events in twentieth-century history.

The giant Apollo rockets built to travel to the Moon were left to rust on the lawns of NASA centers in Florida, Texas, and Alabama, although recently, some have at least been moved indoors to museums (Figure 9.5). It is more than 50 years since astronauts landed on the Moon, and there are no firm plans for future flights. However, both the United States and China are developing the capability to land on the Moon, and there may be a new “space race” in the late 2020s. (In a bizarre piece of irony, a few people even question whether we went to the Moon at all, proposing instead that the Apollo program was a fake, filmed on a Hollywood sound stage. See the Link to Learning box below for some scientists’ replies to such claims.) However, scientific interest in the Moon is stronger than ever, and more than half a dozen scientific spacecraft—sent from NASA, ESA, Japan, India, and China—have orbited or landed on our nearest neighbor during the past two decades.x

Link to Learning

Read The Great Moon Hoax about the claim that NASA never succeeded in putting people on the Moon.

Figure 9.5 : Moon Rocket on Display. One of the unused Saturn 5 rockets built to go to the Moon is now a tourist attraction at NASA’s Johnson Space Center in Houston, although it has been moved indoors since this photo was taken. (credit: modification of work by David Morrison)

Lunar exploration has become an international enterprise with many robotic spacecraft focusing on lunar science. The USSR sent a number in the 1960s, including robot sample returns, and recently China has been active, with three landers and a sample return mission. Of special interest is the search for accessible water ice near the lunar South Pole. Table 9.3 lists some of the most recent lunar missions.

Table 9.3: Some International Missions to the Moon

Launch Year	Spacecraft	Type of Mission	Agency
1994	Clementine	Orbiter	US (USAF/NASA)
1998	Lunar Prospector	Orbiter	US (NASA)
2003	SMART-1	Orbiter	Europe (ESA)
2007	SELENE 1	Orbiter	Japan (JAXA)
2007	Chang’e 1	Orbiter	China (CNSA)
2008	Chandrayaan-1	Orbiter	India (ISRO)
2009	LRO	Orbiter	US (NASA)
2009	LCROSS	Impactor	US (NASA)
2010	Chang’e 2	Orbiter	China (CNSA)
2011	GRAIL	Twin orbiters	US (NASA)
2013	LADEE	Orbiter	US (NASA)
2013	Chang’e 3	Lander/Rover	China (CNSA)
2019	Chang-e 4	Lander/Rover (far side)	China(CNSA)
2020	Chang-e 5	Lander/Sample Return	China(CNSA)

Review of missions to the Moon

just link or create a table?

Notes

 

Roscosmos – Luna 25 

Pioneer/Ranger, Explorer 

Japan – Hiten, Geotail, Nozomi, SELENE, Hakuto-R, SLIM 

US WIND, Clementine, HGS-1, Lunar Prospector, WMAP, SMART-1, STEREO, ARTEMIS, LADEE, TESS, CAPSTONE 

China Chang’e, Chang’e 2, 3, 4, 5,  Queqiao 

Chang’e 4 first to soft land on far side of the moon 

India Chandrayaan, 2, 3 

Chandrayaan 3 soft landed on south pole 

Isreal – Beresheet 

Korea - Danuri 

GRAIL  https://science.nasa.gov/mission/grail/ 

Ebb and Flow 

Measured gravity data 

Mascons (mass concentrations) in basins are mixture of surface rock melt and denser mantle rock that flowed up from below

 

 

Artemis  

Plans for human travel 

Launches a lot of small satellites 

The Race to the Moon

Outline

Race to the Moon  Luna vs. Apollo

1. Soviet Unions and US 
2. USSR gets first robotic missions, image of the far side, lander, rover, robotic sample return 
3. Remote sensing with images
4. Luna Missions
5. NASA lands first people
6. Apollo Missions

Luna Missions

 

 

Luna missions, Zond, KOSMOS 

Russians got first image of far side

Apollo

Spacecraft Design 

Command module  

3 Astronaut living space 

Life support, food, communication, navigation, computers 

Lunar Module 

Had only enough fuel and supplies for trip to Moon and back 

Min weight max manueverability 

2 astronauts – no seats 

Flexible walls 

Legs not strong enough to support the LM on Earth 

Left descent rocket and support stage on the Moon 

Docking – hard 

Transferred rocks and astronauts and jettisoned LM 

Jul 1969 – December 1972 

12 people (1 geologist) 

380 kg of rock – Planetary Materials Laboratory at JSC Houston 

Apollo 11 Mare Tranquilitatis 

Apollo 12 Oceanus Procellarum 

Apollo 13 “Houston, we’ve had a problem” 

Apollo 14 Fra Mauro – ejecta from Mare imbrium  

Apollo 15 Apennine Mountains, Hadley Rille 

Apollo 16, 17 highlands 

Make a table of missions 

Left stuff on the surface 

Flag, rovers, etc 

Sesimometers 

Mirrors? - laser ranging

Remote Sensing w/ Images/ Intro to photogeology 

Image resolution/pixels 

Light direction & shadow –interpreting structures 

False color/representational-color 

Water on the Moon

Most dramatically, water ice has been detected in permanently shadowed craters near the lunar poles. In 2009, NASA crashed a small spacecraft called the Lunar Crater Observation and Sensing Satellite (LCROSS) into the crater Cabeus near the Moon’s south pole. The impact at 9,000 kilometers per hour released energy equivalent to 2 tons of dynamite, blasting a plume of water vapor and other chemicals high above the surface. This plume was visible to telescopes in orbit around the Moon, and the LCROSS spacecraft itself made measurements as it flew through the plume. A NASA spacecraft called the Lunar Reconnaissance Orbiter (LRO) also measured the very low temperatures inside several lunar craters, and its sensitive cameras were even able to image crater interiors by starlight.

The total quantity of water ice in the Moon’s polar craters is estimated to be hundreds of billions of tons. As liquid, this would only be enough water to fill a lake 100 miles across, but compared with the rest of the dry lunar crust, so much water is remarkable. Presumably, this polar water was carried to the Moon by comets and asteroids that hit its surface. Some small fraction of the water froze in a few extremely cold regions (cold traps) where the Sun never shines, such as the bottom of deep craters at the Moon’s poles. One reason this discovery could be important is that it raises the possibility of future human habitation near the lunar poles, or even of a lunar base as a way-station on routes to Mars and the rest of the solar system. If the ice could be mined, it would yield both water and oxygen for human support, and it could be broken down into hydrogen and oxygen, a potent rocket fuel.

 

Clementine, Lunar Prospector, LRO & LCROSS 

 

Detected water in permanently shadowed craters 

Crashed part of spacecraft into crater to create plume – confirmed with other part of LCROSS 

Overall Moon is dry, so water must be remainders of asteroid and comet impacts 

More recent results?? 

Figure 9.2 : Two Sides of the Moon. The left image shows part of the hemisphere that faces Earth; several dark maria are visible. The right image shows part of the hemisphere that faces away from Earth; it is dominated by highlands. The resolution of this image is several kilometers, similar to that of high-powered binoculars or a small telescope. (credit: modification of work by NASA/GSFC/Arizona State University)

Exploration or Geology?

The composition of the Moon is not the same as that of Earth. With an average density of only 3.3 g/cm³, the Moon must be made almost entirely of silicate rock. Compared to Earth, it is depleted in iron and other metals. It is as if the Moon were composed of the same silicates as Earth’s mantle and crust, with the metals and the volatiles selectively removed. These differences in composition between Earth and Moon provide important clues about the origin of the Moon, a topic we will cover in detail later in this chapter.

Studies of the Moon’s interior carried out with seismometers taken to the Moon as part of the Apollo program confirm the absence of a large metal core. The twin GRAIL spacecraft launched into lunar orbit in 2011 provided even more precise tracking of the interior structure. We also know from the study of lunar samples that water and other volatiles have been depleted from the lunar crust. The tiny amounts of water detected in these samples were originally attributed to small leaks in the container seal that admitted water vapor from Earth’s atmosphere. However, scientists have now concluded that some chemically bound water is present in the lunar rocks.

 

 

 

Attributions

https://phys.libretexts.org/Bookshel...es_of_the_Moon 

https://phys.libretexts.org/Bookshel..._Lunar_Surface

https://phys.libretexts.org/Bookshel...Impact_Craters

References

• Bloom, T. F. (1978). Borrowed Perceptions: Harriot’s Maps of the Moon. Journal for the History of Astronomy, 9(2), 117-122. (Original work published 1978)
• Carney, Steven, ed. (2024) Galileo's Observations of the Moon, Jupiter, Venus, and the Sun. NASA Science 
• Chapman, A. (2009), A new perceived reality: Thomas Harriot's Moon maps. Astronomy & Geophysics, 50: 1.27-1.33.
• Stern, S. A. (1999), The lunar atmosphere: History, status, current problems, and context, Rev. Geophys., 37(4), 453–491, doi:10.1029/1999RG900005.
• Van Helden, A. (1995) The Moon, The Galileo Project