A Trusted Friend in a Complicated World

13 Moon Mysteries That Scientists Are Trying to Figure Out

Updated: Dec. 23, 2022

Even though it's right there above us, close enough to visit, scientists still have a lot of questions about Earth's own moon.

1 / 13
Courtesy Travis Burke Photography

Where did the moon come from?

Most scientists agree on the general idea that a Mars-sized object smashed into Earth about 4.5 billion years ago, creating a massive amount of debris that fell into orbit around the Earth and eventually coalesced into a single object. But this mystery isn’t considered solved: “Even where we think we have the very best answers about the moon, we’re still investigating,” says Christopher Palma, a teaching professor at Penn State’s department of astronomy and astrophysics. Here are some more of the biggest unanswered questions about planet Earth.

2 / 13
Courtesy Travis Burke Photography

If that’s how the moon formed, why didn’t the impact knock Earth out of orbit?

One of the most problematic aspects of the collision model is that scientists have a hard time calculating a scenario where the large impactor (which they’ve named Theia) hits Earth with just the right amount of force. “The collision had to be strong enough to throw a huge amount of material up into orbit around the Earth, but not so strong as to destroy the Earth,” Palma says. Plus, the moon’s composition is very similar to the Earth’s, whereas most scientists think the big smash-up should have left the moon being mostly made of debris from Theia. This is why we sometimes see the moon during the day. 

3 / 13
Courtesy Travis Burke Photography

Does that mean the collision theory is wrong?

No, it’s still the dominant idea among moon researchers. The collision between Theia and Earth might have scrambled up all the materials from both bodies, or there might have been multiple collisions with smaller space objects instead of one massive crash.

Scientists are still exploring other theories, including the idea that gravity caused material from the solar system’s formation to coalesce as the two bodies—Earth and the moon—at the same time, and that the moon was already floating around in the solar system before it was drawn in by Earth’s gravity. Both leave even more questions unanswered than the collision theory. These are the mysteries about our universe that scientists still can’t solve.

4 / 13
Courtesy Travis Burke Photography

Is there water on the moon?

Yes! In 2009, NASA sent a rocket into the Cabeus crater, near the moon’s south pole. The crash kicked up a plume of dust that rose almost ten miles above the crater’s rim, while the NASA satellite’s instruments recorded observations. Grains of water ice were part of the cloud, confirming that water exists in permanently shadowed regions near the poles of the moon. We’re not talking about lakes or puddles, but it might be enough to support longer-term human moon missions. “If we land people there,” says Palma, “and if they can retrieve water ice, that means they don’t have to bring it with them.”

5 / 13
Courtesy Travis Burke Photography

How did the water get on the moon?

Researchers think there was a time period when Earth and the moon were being bombarded by comets and asteroids, which contain a lot of water ice, and this might have delivered our own oceans and lakes as well as the moon’s icy deposits. However, a new analysis of moon rocks brought home from the Apollo 15 and 17 missions in the 1970s makes scientists think there was water in the moon’s interior that was brought to the surface during volcanic eruptions. This might also have happened on Earth.

6 / 13

Could there ever have been life on the moon?

One of the reasons scientists want to get a closer look at the ice hidden in polar craters on the moon is that they wonder if it might tell us something about the development of life on Earth. “One idea for the origin of life is that its building blocks were delivered by comets,” Palma says. “There may be remnants of those in the ice on the moon.” Plus, asteroid and comet collisions here could have released material into space that could eventually have made its way to the moon and been preserved there, whereas signs of life from the earliest eras have been destroyed on Earth by weathering and tectonic shifts.

7 / 13
Courtesy Travis Burke Photography

Why do we only see one side of the moon?

We can always see the face of the “man in the moon”—he never shows Earth the back of his head. That’s because the moon is tidally locked to the Earth, meaning that the time it takes the moon to rotate on its axis is the same as the time it takes the moon to orbit once around the Earth (about 28 days). This isn’t actually a mystery to scientists, who explain that it’s a function of the way Earth’s gravitational pull affects the moon. It’s seen in many other planet-moon systems; one of the best examples is Pluto and its moon Charon, which are tidally locked to one another—they’re always facing each other at the same angle and are considered a binary planet system.

8 / 13
Courtesy Travis Burke Photography

Why is the far side of the moon so different from the one we can see?

Because of the tidal locking, humans never saw the other side of the moon until 1959, when the Soviet Luna spacecraft took the first photo. Researchers were surprised to see that it has hardly any of the large lava seas (called maria) that we see on the near side, and is dominated by impact craters. Studies have since shown that the moon’s crust is thicker on the far side, which makes it less likely that volcanic activity would have erupted all the way through to the surface like it did on our side—in the maria we can see, lava welled up into craters and hardened more than a billion years ago when there was still volcanic activity. Don’t miss these other fascinating astronomy facts you never knew.

9 / 13

But why is the crust thicker on the far side?

That’s still a major area of study. “We think part of the difference is because of its tidal locking to the Earth,” says Palma, citing research by one of his Penn State colleagues. When the Earth was molten, it was no doubt radiating a lot more light and heat than it does now, he says. “The side of the moon that locked to Earth got heated up more than the side facing away.”

10 / 13
Courtesy Travis Burke Photography

What are moonquakes?

Although there isn’t any volcanic activity on the moon, there’s quite a lot of seismic activity—sensors placed by Apollo astronauts in the 1970s measured quakes strong enough to destroy a human settlement. Again, says Palma, we’re looking at an effect of the Earth’s tidal pull. While the moon primarily affects tides in Earth’s oceans, our stronger gravitational pull actually deforms the crust of the moon, causing quakes. “There’s also the fact that the side of the moon facing the sun is very hot and the other side very cold, which puts stress on the surface and can cause quakes,” he says.

11 / 13
Courtesy Travis Burke Photography

What is a lunar lava tube?

A Japanese probe using a radar system that can map underground topography recently found a cave 30 miles long and 60 miles wide on the moon. Scientists believe it was formed by volcanic activity at least 3 billion years ago when a flowing stream of lava developed a hard crust on the outside while the molten rock continued flowing through the inside. NASA has found a number of small pits on the moon’s surface that might be openings to similar tubes, and space agencies are optimistic that these underground tunnels would make good locations for manned space missions, and might even be sources of water for astronauts.

12 / 13

Why do wolves howl at the moon?

Well, wolves do howl at night, and sometimes the moon is visible when they’re making a lot of noise, but researchers have actually not been able to confirm that wolves howl any more when the moon is full than during a new moon. Their close relative the domesticated dog, on the other hand, does seem to be affected by moon phases—they visit veterinary emergency rooms 28 percent more often when the moon is full (cats visit 23 percent more often). Full moons also encourage corals to release eggs and sperm and make doodlebugs dig bigger holes. Here are some myths about full moons that you can safely ignore.

13 / 13

Do humans act crazier during full moons?

Aristotle thought the brain might be affected by the moon like tides are because the brain is “moist,” but scientists are now pretty sure that’s not true. Still, cops and emergency room nurses will swear (anecdotally) that their jobs get really crazy during full moons, even though researchers haven’t been able to find any replicable studies showing that crimes, suicides, or psychiatric problems increase then. But there is some evidence that people get about 20 fewer minutes of sleep during a full moon than during a new moon. Next, check out these spooky facts you never knew about the moon.