When Neil Armstrong took his first steps on the moon, it marked a new era not only of humans but also of science.
The 49 lbs. (22 kilograms) of moon rocks and lunar dust returned to Earth by the Apollo 11 mission provided a treasure trove of material that opened the door to insights about another world. Along the way, scientists would glean information about the early days of the solar system and the formation of the Earth, and they would tease out a new understanding of the relationship between our planet and its satellite.
Only six months after the first samples were returned from the moon, in January 1970, the journal Science published an issue devoted to lunar science. Nearly 150 scientific articles discussed new lunar discoveries, most of them focused on studying the samples returned to Earth.
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But lunar science didn't end when Apollo program astronauts stopped carting moon rocks back to Earth. As instruments have grown more advanced and techniques more refined, scientists have continued to glean new information from the ancient moon rocks.
Let's look at some of the key science gleaned from Apollo 11 and its successors.
The lunar surface is solid
Before the astronauts landed, observations from Earth and other landers suggested that the moon was coated with a fine dusting of material. But until right before the crew touched down, there was no way to know how safe the surface might be for human exploration. The material could act like quicksand or be covered in damaging shards. Until astronaut Buzz Aldrin, while about 40 feet above the surface, commented on how the lunar dust churned up by the module struck the moon's surface, the regolith remained a mystery, Apollo researcher Brian O'Brien, a physicist now at the University of Western Australia, said in a statement.
Unlike some later missions, Apollo 11 didn't carry any experiments to pull samples up from below the moon's surface. Instead, the mission relied on astronaut observations of what they saw as they explored the moon, plus the surface samples they brought home. The astronauts' observations combined with telemetry data from the spacecraft allowed scientists to make their first tentative conclusions about the lunar surface.
In particular, those conclusions included that the lunar surface was a mix of tiny grains of dust and larger angular rocks. Some of the rocks sat on the surface, while others were partially or completely buried in the dust. On the lunar surface, the color and brightness of the regolith appeared to change with the viewing angle, although this effect disappeared in labs on Earth. Areas disturbed by astronauts and spacecraft were darker than pristine regions.
The moon is covered with regolith
The regolith of the moon includes fine gray dust and rock fragments from local bedrocks. Apollo 11 samples have also been reported to contain pieces of volcanic glass. Since the moon lacks a substantial atmosphere, the upper layers of lunar regolith are exposed to micrometeorites and solar wind irradiation. The constant hail of micrometeorites breaks up the rocks and melts patches of regolith, creating small glass fragments.
Lunar dust was incredibly aggressive, invading the nooks and crannies of the lunar module, the spacesuits of the astronauts, and even the seals of the sample collection boxes. The explorers easily kicked up the fine-grained material, which tended to adhere to anything it touched because the regolith's electric charge caused a sort of "static cling" that made it even harder to remove.
Before the historic Apollo 11 flight, NASA scientists realized that the lunar module would probably kick up a lot of dust when it launched to return to Earth. The science experiments left behind would be covered with dust. In order to determine just how much dust, O'Brien designed the Lunar Dust Detector (LDD), a small add-on device to the larger experiments that would measure how much dust settled onto the instruments, both from the astronauts' departure and from other sources, such as dust blown up by meteorite strikes.
The LDD allowed researchers to determine that the blanket of departure dust, not radiation, caused a fatal early overheating in the passive seismometer, O'Brien told Space.com by email. Those measurement from Apollo 11 affected the placement of science instruments on future missions, with later astronauts deploying seismometers nearly 10 times farther away from the lunar module.
The moon has a crust, mantle and core like the Earth
Although the Apollo 11 Passive Seismic Experiment lasted only three weeks, it provided a first useful look at lunar seismology. Moonquakes detected by seismometers deployed during Apollo 11, 12, 14, 15 and 16 revealed insight into the lunar layers.
According to David Williams, a planetary scientist at NASA's Goddard Space Flight Center in Maryland, the Apollo 11 instrument revealed that the interior of the moon hides a relatively small solid core spanning less than 25% of the lunar radius, less than half the proportion filled by Earth's solid core.
The seismometer also gave scientists a better look at the moon's upper layer, letting them determine that the lunar crust is between 37 miles and 44 miles (60-70 kilometers) thick, about three times the average crustal thickness of Earth. The seismometers also measured impacts from meteoroids and seismic waves in the crust.
The moon is ancient, and its craters are, too
Samples brought back from the moon helped scientists establish the age of the moon and its surface, suggesting that it formed early in the life of the solar system. "Even the first Apollo 11 samples showed the moon to be about 4.5 billion years old," William Hartmann, a planetary scientist at the Planetary Science Institute, told Space.com by email.
All told, the rocks collected over the Apollo missions range from 3.2 billion years old in the dark, low basins of the maria to nearly 4.6 billion years old in the lighter-colored, rugged highlands.
The samples returned from the Apollo missions also helped scientists date the age of craters on the moon. Until then, geologists had only been able to glean relative ages of impact sites. With the Apollo samples in hand, they were able to directly determine the ages of the regions they sampled, then calculate an approximate age for unsampled basins.
That work paved the way for better understanding of much more distant destinations as well. By setting the age of impacts on the moon during Apollo 11 and subsequent missions, scientists have been able to estimate the age of craters in other parts of the solar system.
Mars, for example, should have received about the same number of impacts as Earth, allowing researchers to date its different landscapes using ages taken from the lunar landscape. Even Pluto's cratering estimates relied on measurements made from the moon's craters!
The moon's rock is lifeless and wet and a lot like Earth's
Scientists analyzed lunar samples for organic material, past or present, and found none. The only traces of non-biological organic material such as amino acids were faint and attributed to meteorites.
Decades after the samples arrived on Earth, scientists also reanalyzed some Apollo moon rocks, including some from Apollo 11, and discovered trace amounts of water in those samples . Researchers determined that the water was delivered to the lunar surface by comets or meteorites (opens in new tab) striking the surface.
These samples have also taught scientists that the moon has a strong chemical similarity to rocks on Earth. Moreover, both are dramatically different from Martian and asteroid belt meteorites.
This profile was one of the things that led Hartmann and his colleague Don Davis to propose in 1974 that the moon formed from debris blown off Earth after a cataclysmic impact early in Earth's lifetime. Their theory remains the leading proposal for how the moon formed.
The moon is moving away from Earth
One of the experiments Apollo astronauts left on the lunar surface was the Laser Ranging Retroreflector. Scientists can precisely measure the distance between Earth and its moon by lighting up the carefully tailored mirrors with laser beams aimed from large Earth-based telescopes.
In addition to improving scientists' knowledge about the moon's orbit and rotation, the experiment also found that the moon is receding from the Earth at a rate of 1.5 inches (3.8 centimeters) per year.
The Laser Ranging Retroreflector "is the only Apollo 11 experiment that is still operational, because it is just a set of mirrors designed to reflect laser pulses from Earth and does not require any power," Williams said.
The solar wind changes
Apollo 11 was the first of several Apollo missions to deploy the Solar Wind Composition Experiment, an aluminum foil sheet deployed on a pole facing the sun. The solar wind is the flood of charged particles streaming off the sun and across the solar system, shaping the environment of all the planets and moons.
In order to better understand what particles are found in that solar wind, the astronauts unfurled the foil sheet, left it exposed to the sun for 77 minutes, then collected it and returned to Earth, where it could be chemically analyzed. Later Apollo crews did the same.
The foil sheets let scientists measure the isotopes of light noble gases in order to understand variations in the composition of the solar wind over the years of the Apollo missions. The variations corresponded to variations in the intensity of the solar wind.
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