"When he dies, take him and cut him out in little stars, and he will make the face of heaven so fine that all the world will be in love with night and pay no worship to the garish sun."
In act 3, scene 2 of Shakespeare's play "Romeo and Juliet," Juliet delivered this soliloquy on the day of her secret wedding, longing for night to fall so she could see Romeo again.
Juliet's lines reached the moon. After completing a 19-month mission, the U.S. lunar probe Lunar Prospector crashed near the lunar south pole on July 31, 1999. Inside was a capsule containing the remains of American geologist Eugene Shoemaker (1928–1997). Juliet's soliloquy was engraved on that very capsule.
Shoemaker made major contributions to the study of meteorite impact craters on Earth. With his wife, Carolyn, and Canadian amateur astronomer David Levy, he also discovered the comet Shoemaker-Levy 9. He took part in the U.S. crewed lunar program in the 1960s but was dropped from the astronaut candidate list due to illness. He fulfilled his dream of becoming the first geologist to go to the moon only after death.
A plaque engraved with the names of 14 American and Soviet astronauts who died during lunar exploration, and the aluminum sculpture "Fallen Astronaut" by Belgian artist Paul Van Hoeydonck. /NASA
A plaque engraved with the names of 14 American and Soviet astronauts who died during lunar exploration, and the aluminum sculpture "Fallen Astronaut" by Belgian artist Paul Van Hoeydonck. /NASA
◇ artifacts of 200 tons left on the moon
The day is approaching when Shoemaker's successors will be able to see Juliet's lines on the moon with their own eyes. The National Aeronautics and Space Administration (NASA) is carrying out the Artemis II mission this year to send four astronauts to the moon. The 10-day flight will be the first crewed lunar mission in 54 years since Apollo 17 in 1972. Artemis II had been scheduled for launch in February but was repeatedly delayed due to launch vehicle issues. The next attempt could come as early as April.
Earlier in 2022, the Artemis I mission conducted an uncrewed test flight, with the Orion spacecraft carrying mannequins into lunar orbit. The Artemis II astronauts will loop around the moon and return, and in 2028, two astronauts on Artemis III are slated to land at the lunar south pole.
What awaits the astronauts on the moon is not only Shoemaker's remains. During lunar exploration half a century ago, the United States and the former Soviet Union left as much as 200 tons of artificial objects on the moon. Most are uncrewed probes and rocket parts, but the equipment and personal belongings that Apollo astronauts brought were also left on the moon as they were. That was to reduce spacecraft weight to carry lunar rocks back to Earth.
The "moon trash" left by humanity has now become historical artifacts. With no wind, no rain, and no atmosphere to cause erosion, the moon serves as a kind of time capsule. Everything is preserved exactly as it was left. Not only metal equipment but also astronauts' waste bags and vomit traces, abandoned to cut spacecraft weight, are presumed to remain intact.
◇ a list and sculpture honoring the fallen
Astronauts did not leave only trash. Some mementos were taken to the moon on purpose. Charles Duke of Apollo 16, which landed on Apr. 20, 1972, left a family photograph on the lunar surface. At 36, Duke set the record as the youngest person to walk on the moon. The photo should still be there, though its colors likely bleached white due to radiation from the sun.
There are also memorials honoring fellow astronauts. The Apollo 11 crew left the Apollo 1 mission patch on the moon to honor three astronauts who died in a fire during a simulated launch in 1967. Alan Bean of Apollo 12 left the silver astronaut pin of Clifton Williams, who was killed in a jet training crash, to honor him. Astronauts receive a silver pin before flying to space and a gold pin after. Bean went to the moon in Williams' stead.
The Apollo 15 astronauts who went to the moon in 1971 left on the moon a list of 14 astronauts who died in lunar programs, including those from the Soviet Union as well as the United States. Soviet cosmonaut Yuri Gagarin, who became the first human in space aboard Vostok 1 on Apr. 12, 1961, was included. He died in a training crash in 1968. In front of the list, they placed an 8.5-centimeter aluminum astronaut sculpture by Belgian artist Paul Van Hoeydonck.
There was also a scientist who drew renewed attention on the moon before Shoemaker: Galileo Galilei of Italy. The Apollo 15 astronauts, the fourth crew to land on the moon in 1971, dropped a 1.32-kilogram hammer and a 30-gram falcon feather simultaneously from a height of 1.6 meters above the lunar surface as the world watched.
In the 16th century, Galilei argued that in a vacuum, objects fall at the same speed regardless of mass. As he said, the hammer and feather touched the lunar surface at the same time. Although he was said to have conducted this experiment from the Leaning Tower of Pisa, in reality it was a thought experiment done in his mind.
◇ scientific instruments still working
Among the objects left on the moon are some that still exchange signals with Earth. A few hundred meters from the first footprints left on the moon by Apollo 11's Neil Armstrong is a retroreflector array. In this suitcase-sized device, 100 mirrors are densely embedded. At the Apache Point Observatory in New Mexico, the United States, scientists fire lasers at the lunar reflector on clear nights. The light reflects off the lunar mirrors and returns to Earth.
The reflector tells us the distance from Earth to the moon. Since the speed of light is known, if we measure the round-trip time, we can determine the roughly 385,000-kilometer Earth-moon distance down to millimeters. Using the reflector, scientists tested Einstein's general theory of relativity and discovered that the moon has a liquid core.
There are currently five reflectors operating on the moon. Three were sent by the United States and two by the Soviet Union. One of them is on Lunokhod 1, the Soviet lunar rover that went to the moon in 1970. Missing for 40 years, Lunokhod 1 was found in 2010 by American scientists using high-resolution cameras on NASA's Lunar Reconnaissance Orbiter (LRO).
Just as archaeologists on Earth search for sites left by ancestors, some scientists hunt for spacecraft and equipment that vanished on the moon. They are space archaeologists. In January, British and Japanese space archaeologists announced they had found an object believed to be Luna 9, a Soviet uncrewed spacecraft that had gone silent for 60 years. On Feb. 3, 1966, Luna 9 became the first spacecraft in history to make a soft landing on the moon and transmit images of the lunar surface to Earth.
The British and Japanese scientists used artificial intelligence (AI) to analyze LRO images of the lunar surface and found Luna 9. Last month, Russian science writer Vitaly Yegorov also said he had pinpointed Luna 9's landing site. It was an achievement won by human persistence rather than AI. He painstakingly compared the four lunar surface photos sent by Luna 9 with the 3D lunar topographic maps produced by NASA's LRO. By studying the images, he identified the photo locations.
◇ water bears may still be alive on the moon
People long ago thought the moon's markings looked like a rabbit pounding rice cakes. China named its lunar rover Yutu (Jade Rabbit) for that reason. There is a different animal on the moon instead of a rabbit.
Israel's uncrewed probe Beresheet crashed while attempting a lunar landing on Apr. 11, 2019, and inside was a capsule carrying thousands of tardigrades, known as the "toughest animals on Earth." Tardigrades are close to arthropods and measure no more than 1.5 millimeters long. They move on eight legs and live on moss, feeding on plankton. They were named for their bear-like shape as they swim through water.
Although the probe was destroyed, the tardigrades may have survived. Tardigrades can live more than 30 years without water or food. They withstand extreme cold at minus 273 Celsius and scorching heat up to 151 degrees. Most animals die from radiation doses around 10–20 Gy (gray), but tardigrades endure a staggering 5,700 gray.
Tardigrades have, in fact, survived in space. In 2007, the European Space Agency (ESA) launched tardigrades into space aboard an uncrewed spacecraft. When moisture was provided after they returned to Earth 12 days later, some revived. Before tardigrades, only mosses and bacteria had survived the deadly radiation of the vacuum of space.
Is it acceptable to send Earth organisms to the moon at will? When sending probes to Mars, NASA thoroughly sterilizes spacecraft to guard against contaminating extraterrestrial ecosystems with Earth life. The moon is an exception, however, because it has already been concluded that no life exists there. That is why Apollo astronauts left 96 bags of waste containing gut bacteria on the moon.
But circumstances have changed as the possibility emerged that organic compounds tied to the origins of Earth life may exist in ice at the lunar south pole. Moreover, the revived lunar program after half a century is pushing not just one-off landings but also a crewed base for long-term stays. Elon Musk of SpaceX, who once championed a Mars colony, also revised priorities to put lunar exploration first. The moon is rising not as a wasteland where trash can be dumped anywhere, but as a land of new opportunity. We must not repeat on the moon the mistakes made on Earth.