Science News for Students is celebrating the 50th anniversary of the moon landing, which passed in July, with a three-part series about Earth’s moon. In part one, Science News reporter Lisa Grossman visited rocks brought back from the moon. Part two explores what astronauts left on the moon. Look for part three in November, and check out our archives for this story about Neil Armstrong and his pioneering 1969 moonwalk.
Fifty years ago, astronauts first walked on the moon. Part of NASA’s Apollo program, they kicked off six missions to visit Earth’s lunar neighbor. Once on the moon, Apollo astronauts had two main goals: Get themselves and the moon rocks they gathered home safely.
That meant making space on cramped lunar modules for around 360 kilograms (about 800 pounds) of moon samples. Anything they didn’t need for the ride home got tossed — cameras, hammocks, boots and trash. They even ditched big stuff like moon buggies and launchpads.
But the astronauts left more than trashed castoffs. The crews marked their visits with six American flags and plenty of keepsakes. They also left behind about a dozen experiments to keep tabs on the moon. One still runs today.
These experiments were important parts of Apollo, says Noah Petro. He is based at NASA’s Goddard Space Flight Center in Greenbelt, Md. There he works as a project scientist for the Lunar Reconnaissance Orbiter mission. Its aim has been to map the moon.
Back in the Apollo era, the experiments didn’t get much attention, Petro notes. That’s because the big story was sending humans to the lunar surface.
When we think of Apollo’s 50-year legacy, most of us aren’t picturing astronaut junk gathering space dust. But nations are planning new ventures to the moon. So researchers are now thinking about how to prevent future lunar visitors from erasing the marks of humans’ first footsteps beyond Earth.
Setting up a lunar lab
The six moon missions ran from 1969 to 1972. Apollo crews spent a total of nearly 80 hours exploring the lunar surface. They gathered rocks, took photos of the moon’s surface and did many types of experiments. Astronauts caught particles of the solar wind with metal foil. They even set off explosives to measure the resulting tremors.
The first mission to the moon, Apollo 11, planted solar-powered seismometers. These devices detect and measure moonquakes — tremors that pass through the moon. The astronauts also left behind mirrors. When paired with lasers on Earth, the mirrors can be used to precisely measure the distance between Earth and the moon.
Astronauts left more elaborate setups during other Apollo missions. Some of the nuclear-powered devices collected data through 1977. As NASA decided to focus on other projects, it pulled the plug on the whole operation.
The data sat unstudied for years, Petro says. But within the last decade, a new generation of scientists has taken up the torch. They are analyzing Apollo observations to answer some lingering questions.
Solving old mysteries
This task isn’t as simple as picking up where 1970s scientists left off. That's what Seiichi Nagihara discovered. A geophysicist at Texas Tech University in Lubbock, he set out to solve a decades-old puzzle about the moon’s temperature.
On Apollo 15 and 17, astronauts installed thermometers in the lunar surface. These took the moon’s temperature at various depths and sent those data back to Earth. Apollo-era scientists reviewed data collected through 1974. The results showed something odd. The moon’s temperature just beneath the surface was slowly rising.
“We’re talking about very minor warming,” just a couple of degrees, says Nagihara. But researchers at the time couldn’t figure out why it was happening. So Nagihara decided to examine all the temperature data collected through 1977. Sadly, the tapes that recorded these measurements were missing. This is a common problem. During the Apollo era, data were housed at the individual labs of scientists. Many measurements were never properly archived.
“A group of us decided to … try to hunt down the tapes,” Nagihara says. They scoured thousands of documents at NASA’s Johnson Space Flight Center in Houston, Texas. The researchers tracked down 440 tapes held in an archive in Maryland. But those covered only about three months of observations.
Luckily, Nagihara’s team discovered weekly memos that noted more temperature data. These had been archived at the Lunar and Planetary Institute in Houston. The team used these data to piece together a picture of the moon’s temperature from 1971 through 1977.
The surface was still slowly warming when data collection ended. In search of a heat source, the researchers turned to pictures taken by the Lunar Reconnaissance Orbiter.
This spacecraft has been orbiting the moon since 2009. Its images showed that soil stirred up by astronauts was slightly darker than other lunar terrain. Perhaps it was dark enough to absorb more sunlight and warm the ground below.
Computer models would confirm that the moon wasn’t heating up from the inside out.
Astronauts trekking around the moon’s surface probably caused it to heat up by about 2 to 3 degrees Celsius (about 4.5 to 5.5 degrees Fahrenheit). And the extra heat slowly spread more than a meter (3 feet) into the ground. That caused the warming detected by Apollo instruments. Turns out those footsteps had left marks on the moon far deeper than those iconic boot prints.
The researchers reported the findings in April 2018 in the Journal of Geophysical Research: Planets.
Keeping vigil over gravity
Nagihara and other researchers dig up and analyze old Apollo data. But one lone project is still in full swing: a laser “yardstick” to measure the distance between Earth and the moon.
It’s called the laser ranging retroreflector experiment. It relies on those special mirrors that astronauts placed on the moon by astronauts on the Apollo 11, 14 and 15 missions. Each mirror has three sides, shaped like a cube’s corner. When light hits the corner, it will always reflect in the exact direction from which it came. Researchers shoot a laser beam at these mirrors from a telescope on Earth. They then clock the time it takes for the light to return.
These measurements have offered several insights. For instance, they showed the moon is moving away from Earth at about 3.8 centimeters (1.5 inches) per year. And slight variations in the moon’s rotation suggest that this body has a relatively small core.
Physicist Tom Murphy is using the mirrors to answer a question much bigger than the moon. He’s testing the equivalence principle — a key part of Einstein’s theory of gravity.
That equivalence principle states that any two objects in the same field of gravity should fall at the same rate. A bowling ball and a ping-pong ball should hit the ground at the same time (at least if they fall in a vacuum). And the Earth and moon should orbit around the sun at exactly the same rate. If the orbital rate breaks with this principle, that would reveal a flaw in the theory.
Einstein’s theory doesn’t mesh with quantum mechanics. That’s the physics of very small objects. Something has to give. This principle might be one of those things, says Murphy, at the University of California, San Diego. If scientists manage to prove Einstein wrong, it could lead to a new theory that unites his with quantum mechanics.
So far, the Earth and moon orbit the sun at the same rate. But in 2006, Murphy started collecting data with more precision. It will take years more to get enough data and better computer models to analyze it, Murphy says. Luckily, the mirrors on the moon don’t require any power, so he can collect data into the foreseeable future. Eventually, those fine-scale observations could reveal a crack in the principle.
One astronaut’s trash
About a dozen types of instruments were installed on the moon. Some measured its magnetic field. Others sniffed out the chemical makeup of its fragile atmosphere. NASA’s Lunar Data Project is restoring data from these and other Apollo experiments. That way, scientists can continue to pore over the observations for years to come.
“When you have this incredibly rare resource, you can’t not keep working on it,” says planetary scientist Renee Weber. She studies lunar seismic data at NASA’s Marshall Space Flight Center in Huntsville, Ala. “There are always new techniques to try” and better computers to tease out missed signals.
Moonquakes sensed by Apollo seismometers hint that the moon may still be tectonically active. And young faults on the lunar surface support this idea, Weber’s team reported in May. Understanding moonquakes could help NASA and other agencies decide where to land future spacecraft, Weber says. Or where to construct buildings on the moon. If these young faults mark sites of ground-shaking activity, future lunar visitors may want to avoid them, she says.
There’s also plenty to learn by testing how well the Apollo instruments and astronaut leftovers have held up. All of that stuff has been exposed to the lunar elements for decades. Future missions could sample the debris to get a sense of how human communities might one day fare on the moon.
Everything at these sites is priceless to research, says planetary scientist Philip Metzger. He works at the University of Central Florida in Orlando. He imagines probing the effects of radiation and solar wind on things like batteries, camera lenses, towels and earplugs.
There’s even value in bags of astronauts’ poop. Studies show microbes can last in space over very short timescales, Metzger says. Scientists could test whether microbes in astronaut waste have survived or mutated over the past 50 years. That could help determine whether life could hop between planets or even solar systems. These are “really important questions,” he says, “about the position of life in the cosmos.”
Apollo 11 The first space flight ever to land humans on the moon. Two astronauts, named Neil Armstrong and Buzz Aldrin, landed there on July 20, 1969. They spent nearly 22 hours on the moon. They collected a handful of rocks and other samples that were returned home for scientists to study.
Apollo missions NASA’s third human spaceflight program eventually took humans to the lunar surface. Along the way, this program sought to develop the technologies needed for long-distance space travel. It got a big kick-start after President John F. Kennedy proposed in 1961 creating the national goal of “landing a man on the Moon and returning him safely to the Earth.”
archive (adj. archival) To collect and store materials, including sounds, videos, data and objects, so that they can be found and used when they are needed. The term is also for the process of collecting and storing such things. People who perform this task are known as archivists.
astronaut Someone trained to travel into space for research and exploration.
atmosphere The envelope of gases surrounding Earth or another planet.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
computer model A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
core Something — usually round-shaped — in the center of an object. (in geology) Earth’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.
cosmos (adj. cosmic) A term that refers to the universe and everything within it.
data Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.
element A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.
fault In geology, a fracture along which there is movement of part of Earth’s lithosphere.
field An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory. (in physics) A region in space where certain physical effects operate, such as magnetism (created by a magnetic field), gravity (by a gravitational field), mass (by a Higgs field) or electricity (by an electrical field).
focus The point at which rays (of light or heat for example) converge sometimes with the aid of a lens. (In vision, verb, "to focus") The action a person's eyes take to adapt to light and distance, enabling them to see objects clearly.
generation A group of individuals (in any species) born at about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans. The term also is sometimes extended to year classes of other animals or to types of inanimate objects (such as electronics or automobiles).
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
insight The ability to gain an accurate and deep understanding of a situation just by thinking about it, instead of working out a solution through experimentation.
journal (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.
laser A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.
lunar Of or relating to Earth’s moon.
magnetic field An area of influence created by certain materials, called magnets, or by the movement of electric charges.
mechanics The study of how things move.
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
model A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.
module A set of standardized parts or independent units used to assemble a more complex structure. The module could be used to create a “prefabricated” home or furniture — or even a spacecraft.
moon The natural satellite of any planet.
NASA Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.
orbit The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.
orbital Adjective for something relating to orbits. (in chemistry and subatomic physics) The pattern(s) of electrons (and their density) that form(s) within an atom or molecule.
orbiter A spacecraft designed to go into orbit, especially one not intended to land.
particle A minute amount of something.
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.
pore A tiny hole in a surface. On the skin, substances such as oil, water and sweat pass through these openings.
quantum (pl. quanta) A term that refers to the smallest amount of anything, especially of energy or subatomic mass.
quantum mechanics A branch of physics dealing with the behavior of matter on the scale of atoms or subatomic particles.
radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
satellite A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.
seismometer (also known as a seismograph ) An instrument that detects and measures tremors (known as seismic waves) as they pass through Earth.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
solar wind A flow of charged particles (including atomic nuclei) that have been ejected from the surface of the star, such as our sun. It can permeate the solar system. This is called a stellar wind, when from a star other than the sun.
star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
telescope Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
terrain The land in a particular area and whatever covers it. The term might refer to anything from a smooth, flat and dry landscape to a mountainous region covered with boulders, bogs and forest cover.
Texas The second largest state in the United States, located along the southern border with Mexico. It is about 1,270 kilometers (790 miles) long and covers an area of 696,000 square kilometers (268,581 square miles).
theory (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.
vacuum Space with little or no matter in it. Laboratories or manufacturing plants may use vacuum equipment to pump out air, creating an area known as a vacuum chamber.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
Journal: S. Nagihara et al. Examination of the Long-Term Subsurface Warming Observed at the Apollo 15 and 17 Sites Utilizing the Newly Restored Heat Flow Experiment Data From 1975 to 1977. Journal of Geophysical Research: Planets. Vol. 123, May 2018, p. 1125. doi: 10.1029/2018JE005579.
Journal: T.R. Watters et al. Shallow seismic activity and young thrust faults on the moon. Nature Geoscience. Vol. 12, published online May 13, 2019, p. 411. doi: 10.1038/s41561-019-0362-2.