By Sabine Stanley, Ph.D., Johns Hopkins University
A peek inside the inner workings of the Apollo program: from the first landing of Apollo 11 to the last landing of Apollo 17, and from the oldest discovery made on the Moon to the latest one.
(Image: Merlin74/Shutterstock)
The human adventure in space truly began when we set foot on the Moon. From that first step on July 20th, 1969, to the end of 1972, 12 astronauts walked on the Moon at six different landing sites. Apollo 11 in 1969 was the first mission that landed humans on the Moon, and by the end of 1972, there had been six successful human landing missions during just a 4-year period.
Apollo 11: The First Landing on the Sea of Tranquility
The first landing was in Mare Tranquillitatis, the Sea of Tranquility. But the Sea of Tranquility is not actually a sea. It is an impact crater that was filled in with lava that solidified into rock billions of years ago.
The astronauts who landed on the Moon became immediately aware that the surface is covered in a layer of loose dust and broken rock, known as regolith. This is the end result of the Moon’s surface having been impacted over and over again for 4.5 billion years.
Before the first landing, there was a concern that the regolith would be so fine and loose that the astronauts and lunar module might sink quite deep into it. This was why Neil Armstrong was commenting on the LM footpads of the Lunar Module just before taking his first step: “I’m at the foot of the ladder. The LM footpads are only depressed in the surface about one or two inches, although the surface appears to be very, very fine-grained, as you get close to it. It’s almost like a powder. Ground mass is very fine.”
So it turned out only the top few centimeters were fine enough for a boot to leave an imprint. The rest is quite firm, compacted, and altered from intense space weathering.
Astronauts Neil Armstrong and Buzz Aldrin spent just over two hours of their 21-hour visit walking on the Moon’s surface and collected 22 kilograms of lunar rocks to take back to Earth.
The Other Apollo Landings on Moon
Apollo missions landed in a ring of locations on the Moon’s nearside surface: Apollo 12 and 14 south of the Copernicus crater, Apollo 15 southeast of the Archimedes crater, Apollo 16 southwest of Apollo 11, and Apollo 17 in the highlands on the southeast corner of the Sea of Serenity. The missions carried out science activities such as placing seismometers, magnetometers, and retroreflectors on the surface, and also collected lunar samples to return to Earth.
The lunar samples collected by the Apollo astronauts have helped unlock scientific mysteries such as how old the Moon is, how it formed, and what it is made of. During the last three Apollo missions, astronauts were driving around the surface in a Lunar Roving Vehicle. This made it possible to cover 10 times as much distance and gather up far more samples.
This is a transcript from the video series A Field Guide to the Planets. Watch it now, Wondrium.
The Significance of the Apollo Program
The Apollo program was revolutionary for many reasons. It led to a series of robotic missions, including Clementine in 1994, Lunar Prospector orbiter in 1998 and 1999, LCROSS in 2009, GRAIL in 2012, and LADEE in 2013 and 2014, just to name a few. Signs of the Apollo missions on the Moon persist to this day. There are various pieces of equipment and spacecraft parts left on the surface, still providing us with important data.
The Apollo missions, in all, collected 2200 rock samples, weighing almost 400 kilograms, all brought back to Earth for analysis. The analysis of those rocks on Earth have helped us determine that the Moon has a similar composition to the Earth’s mantle and that the Moon formed very early in solar system history.
Learn more about Mars from space and the ground.
Determination of the Age of the Lunar Surface
One of the most important discoveries was the determination of the age of different parts of the lunar surface. Now, we can tell the relative ages of parts of a planetary surface by looking at how cratered the surface is. For example, Mare Tranquillitatis, where Apollo 11 landed, has fewer craters than some of the highland regions just to the southwest of it. This tells us Tranquillitatis is younger than the highlands. But we need radiometric dating of the rocks to tell the absolute age—that is to put a number on the age.
Learn more about exploring the Earth-Moon system.
Crater Counting or Theoretical Determination of a Planet’s Age
Samples from Mare Tranquillitatis tell us that it is between 3.6 to 3.9 billion years old. This is key because once we know the absolute age of a rock coming from one region, and we know the crater density of that region, we can figure out the ages of other regions on the surface with the same crater density, even if we don’t have samples.
So we can figure out the ages of large regions of the Moon’s surface from just a handful of samples. And, more importantly, we can translate that information to figure out the absolute ages of the surfaces of other planets even if we don’t have samples.
Crater counting is how we know the surface of Venus is around 200 million to a billion years old, even though we have no samples from Venus. Looking up at the full Moon from Earth, we can already see features on its surface.
Learn more about orbiting Earth: up through the atmosphere.
Apollo Mission’s Equipment on the Moon
Apollo missions left behind many different types of equipment on the Moon. First, there are laser retroreflectors that are used to study the rotational and orbital motion of the Moon. The basic idea is that if you aim a laser pulse at the Moon and measure how long it takes for that pulse to reflect back, then we can calculate the distance between Earth and the Moon very precisely—down to just a few centimeters, in fact.
This technique has been used to figure out the speed at which the Moon is moving away from Earth, and even to test Einstein’s general theory of relativity since it makes predictions about the Moon’s orbit. Even changes in the Moon’s rotation and wobble in its orbit have been measured and tell us about the deep interior of the Moon.
The Apollo missions also left seismometers on the surface of the Moon that have given us data about moonquakes. There are deep moonquakes, that are likely to be due to tidal flexing of the Moon, but there are also shallow moonquakes, ranging from 2 to 5 on the Richter scale. They are caused by tidal forces in combination with the Moon shrinking as it continues to cool. The moonquakes also made it possible to determine that the Moon has a small iron core, only to the diameter of Earth’s iron core.
The Moon doesn’t have a global magnetic field generated by a dynamo today, but the iron core is at least partially liquid. This liquid part of the core leaves open the possibility that the Moon did have a dynamo in its past.
Even some lunar samples are magnetized. Based on the ages of the magnetized lunar samples, scientists have determined that a dynamo was active by at least 4.2 billion years ago and may have lasted until just a mere 1 billion years ago.
The Apollo missions continue to yield new findings. For example, in 2019, researchers announced that a sample gathered by Apollo 14 was a rock over 4 billion years old that was likely to have come from Earth. If correct, this fragment, weighing nearly two grams and brought back from the Moon, may be our oldest non-microscopic rock sample of Earth itself.
Common Questions about the Apollo Program
The Apollo 13 accident and the development of cheaper and safer robotic lunar exploration were the main reasons behind the end of lunar missions.
The Apollo missions that landed on the Moon returned a wealth of scientific data and nearly 400 kilograms of lunar samples, which are still being used for new discoveries.
The total cost of the Apollo program was about 25 billion dollars and about 152 billion in today’s dollars.
Apollo 1 or AS-204 was the first crewed mission of Apollo programs. A cabin fire during one of the rehearsal tests broke out and led to the death of all three astronauts.
