It took less than a week NASA Administrator Bill Nelson’s gaffe made it to social media.
More than an hour after the start of a hearing on the US budget Space A congressman asked Nelson why China was sending spacecraft to the “back side” of the moon.
“You’re going to have a lander on the far side of the moon, the side where it’s always dark,” Nelson, a former senator and astronaut, said during the mission the April 17 hearing. “We don’t plan on going there.”
He then told lawmakers: “We don’t know what’s on the far side of the moon.”
This was wrong in two respects: Contrary to popular belief, the so-called far side of the moon is neither dark nor completely unknown to American scientists.
NASA is back in the moon business. Here’s what that means.
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What is the dark side of the moon?
The other side is the hemisphere of the moon facing away from Earth. Because people never see it, this part was once called “the dark side.” The confusing misnomer has led many to incorrectly believe that the other side is shrouded in darkness. In reality, it receives just as much light as the front.
Maybe it’s the actual “dark” place on the moon where NASA plans to send Artemis astronauts in the coming years: the polar southern region, where scientists believe ice water is buried. The south is dotted with ice-cold craters shrouded in shadow.
The other side is the hemisphere of the moon facing away from Earth.
Photo credit: NASA/NOAA
Why do we only see one side of the moon?
It takes about a month for the moon to appear. about 250,000 miles awayto orbit the Earth. It also takes the same amount of time for the moon to complete a full rotation on its axis. This coincidence is the reason why earthlings always see the same side of the moon.
Before space exploration, many speculated that the other side was a frozen and threatening region, a myth perpetuated by Pink Floyd’s trippy 1973 album Dark Side of the Moon.
As a matter of fact the other side remained a mystery to people, but only until October 1959. At that time, the Soviet space program swung the Luna 3 probe around the moon. The spacecraft provided several grainy images that provided insight a strangely different surface than that on the familiar near side.
Destructible speed of light
About half a century later, NASA launched this Lunar reconnaissance orbiter to explore the region from space. Since then, the spacecraft has sent back a ton of data that will allow scientists to map the backside in detail.
The Soviet space program orbited the Luna 3 spacecraft around the moon in October 1959.
Photo credit: Luna 3 / Russian Space Agency / NSSDCA
What does the other side look like?
Scientists have discovered that the side that humans can’t see is completely different.
Although the front has large dark spots that together resemble a face known as the “Man in the Moon,” there are few of these spots on the other side. The Spots are called Mary, dark areas formed when meteoroids hit the moon and spewed lava. The lava not only darkened the surface, but also obliterated previous craters that documented some of the moon’s geological history.
The other side, however, is covered by other craters of varying sizes and depths, including the huge South Pole-Aitken Basin.
During the era of NASA and the Soviet space race, spacecraft never landed on the invisible side. Part of it was because of that how difficult it is. The moon itself blocks communication between mission leaders on Earth and the other side. But in 2018, China launched a communications satellite about 40,000 miles beyond the moon that could exchange signals.
The far side of the moon receives just as much light as the near side.
Image credit: NASA/USRA/GSFC visualization
Why is China flying to the other side of the moon?
Back to the April 17 House Appropriations Committee hearing: U.S. Rep. David Trone asked Nelson what he did China is so interested in the other sideand not the South Pole.
“I have no idea,” Nelson said. However, he explained that the US is flying to the moon’s south pole because NASA suspects water is preserved in dark craters there. It is an important economic resource for future lunar projects.
But scientists say there’s actually a lot to be gained by examining the other side, which appears to have a more pristine past cosmic collisions and effects.
NASA’s Moonkam looks at the far side of the moon.
Image credit: NASA / Caltech-JPL / MIT / SRS
On December 8, 2018, China launched the Chang’e-4 mission and became the first country land on the far side of the moon. It landed at Von Karman Crater, a site in the South Pole-Aitken Basin.
The basin is a depression likely formed by an ancient asteroid collision that was so catastrophic that it hollowed out part of the moon’s mantle – material between the core and the crust – and brought it to the surface. The advantage of visiting this place is that one can learn more about the internal composition of the moon.
What China found loud an article published in the diary Scientific advances, is that the soil layer there is much thicker than on the opposite side. It was about 130 feet deep.
If the crust were much thinner on the side facing Earth, that could explain why lava was able to break through and form the Maria patches. But why the crust of one hemisphere differs so much from the thickness of the other is unclear. China’s future missions can help answer this question.
Solving such mysteries could not only tell us more about the evolution of the moon, but also provide further insights into the history of the solar system.