254: Chapter 254: The lunar craters are only 6 kilometers wide.

Jiang Zhe operated his tablet to pull up a high-definition image of the lunar surface, where densely packed craters covered the entire sphere like machine-gun fire.

"Look, the Moon is covered in craters of all sizes. On one hand, this is because there is no atmosphere to protect it, so any small celestial body can crash directly into it."

He tapped lightly on the screen, zooming in on one of the typical craters.

"But on the other hand, these craters all have one thing in common: they are all approximately 6 kilometers deep."

Xiao Yu was stunned for a moment. "Huh? All of them are 6 kilometers deep? What does that mean?"

Jiang Zhe pulled up another set of data: [Data on Famous Lunar Craters]

Gagarin Crater: Diameter approximately 300 km, depth approximately 6.4 km.

Clavius Crater: Diameter approximately 240 km, depth approximately 6 km.

Bailly Crater: Diameter approximately 295 km, depth approximately 6 km.

Newton Crater: Diameter approximately 230 km, depth approximately 6 km.

Tycho Crater: Diameter approximately 85 km, depth approximately 4.5 km.

"Look," Jiang Zhe pointed at the data, sliding from top to bottom, "From the large craters with a diameter of 300 kilometers to the medium-sized ones with diameters of tens of kilometers, the depth is basically around 6 kilometers. Tycho Crater is slightly shallower, but it's not that different."

Xiao Yu leaned closer to the screen and couldn't help but ask, "So, you mean no matter how big the meteorite is, the depth of the crater it creates is about the same?"

"Correct." Jiang Zhe nodded slightly. "According to common sense, large craters should be deeper and small craters should be shallower. That would be logical, right?"

Then Jiang Zhe pulled up another set of data: [Data on Famous Terrestrial Craters]

Barringer Crater: USA, diameter 1.2 km, depth approximately 170 meters.

Sudbury Crater: Canada, diameter approximately 250 km, depth approximately 15-20 km.

Vredefort Crater: South Africa, diameter approximately 300 km, depth approximately 25-30 km.

"The Moon's craters are a bit strange, whereas the craters on our Earth have a depth that is proportional to their diameter." Jiang Zhe pointed at the data. "A crater with a diameter of 1 kilometer has a depth of about a hundred meters, while a crater with a diameter of several hundred kilometers has a depth of tens of kilometers. This is the normal form of an impact crater."

"As the name implies, the larger the crater, the deeper it is. This is very consistent with physics!"

Xiao Yu nodded thoughtfully.

At this moment, in the livestream chat, viewers were frequently sending messages.

"I know this, the teacher mentioned it during astronomy class!"

"Yeah, it's just that no matter how big the meteorite that hits it is, it only creates a 6-kilometer-deep crater."

"Is it that it can't dig deeper once it hits 6 kilometers?"

"Is the Moon wearing armor?"

"It's so amazing, I never noticed this detail before!"

Jiang Zhe continued, "According to the laws on Earth, those large craters on the Moon—for example, the South Pole-Aitken basin with a diameter of 1300 kilometers—if calculated according to the normal depth-to-diameter ratio, its depth should be 55 to 65 kilometers."

"But in reality, its depth is still around 6 kilometers."

"If that meteorite had hit Earth, how deep would it have been?"

"It wouldn't be less than 100 kilometers." Jiang Zhe smiled. "But on the Moon, it's only 6 kilometers. It gives the impression that the Moon seems to have a particularly hard shell, and that shell is located 6 kilometers underneath."

Principal Fu's office.

Ren Xiaoyao saw this scene, and his eyes lit up.

"Yes, that's it!"

He turned around to look at Principal Fu, Old Wang, Xiao Wang, and Old Yu the Physicist.

"The largest crater on the Moon is the South Pole-Aitken basin, with a diameter of 2600 kilometers; no, to be precise, it's about 1300 kilometers. I remembered it wrong."

"According to the formula used on Earth, a crater of this size should normally be 55 to 65 kilometers deep."

"But in reality, it's only 6 kilometers."

Old Yu the Physicist frowned. "Why is that?"

Ren Xiaoyao shook his head. "It's hard to say. One explanation is that there is some kind of particularly hard structure beneath the lunar surface, and the meteorite cannot dig any deeper once it hits that depth. But even if it is a hard shell, it is not necessarily a definitive conclusion. There are currently many possibilities; it could be a difference in material composition, different physical processes during the impact, or it could be..."

He paused for a moment and didn't continue.

Xiao Wang couldn't help but ask, "What else could it be?"

Ren Xiaoyao glanced at Xiao Wang. "It could also be that there is something inside the Moon blocking the meteorite's impact."

Qingfeng Temple.

Zheng Ming pursed his lips, his brows furrowed.

"A 6-kilometer-deep shell, what kind of theory is this?"

Robert, who was beside him, didn't speak. He felt that this knowledge was very basic; if this was the extent of Jiang Zhe's level, then he feared Jiang Zhe was nothing more than someone seeking fame and reputation.

Only if he could explain these unsolved mysteries in a convincing way would he admire Jiang Zhe.

After a long while, Robert shook his head.

The villa living room.

Jiang Zhe looked at Xiao Yu's confused expression and smiled slightly.

"As for why this phenomenon exists, there is actually a very interesting answer."

Having said that, he pulled up another image: Jupiter's moon, Europa.

"When astronomers observed Jupiter's moons, they found that some of the craters on these moons had similar characteristics: no matter how large the diameter was, the depth was about the same."

"Later research discovered that this was because the surfaces of these moons were covered with a thick layer of ice."

"When a meteorite impacts, the heat generated melts the ice layer, and the melted water flows into the crater, then refreezes, filling the crater up."

"In other words, no matter how deep the crater was initially, it would eventually be 'repaired' by the ice layer to about the same depth."

Xiao Yu's beautiful eyes slowly widened. "So the Moon..."

"Yes, as you thought." Jiang Zhe nodded slightly and said with a certain expression, "Based on this analogy, the lunar surface may have also been covered with a thick layer of ice a long time ago."

"The process is as follows: a meteorite strikes the lunar surface at high speed, creating a large crater tens of kilometers deep. The immense heat generated by the impact causes the surrounding ice layer to melt instantly, and the melted water flows into the crater. But as time passes, the water temperature drops and it refreezes into ice."

"Eventually, that large, tens-of-kilometers-deep crater is filled by ice into a shallow crater only a few kilometers deep."

In the animation, under time acceleration, the deep lunar craters were slowly filled with white ice, leaving behind only a shallow depression; then, more and more lunar dust filled the deep craters.

After watching the animation, Xiao Yu couldn't help but cover her mouth. "I thought the Moon had always been like this!"

"Therefore!" Jiang Zhe smiled. "What you think is not necessarily the truth."

Qingfeng Temple.

Zheng Ming finally couldn't hold it in anymore and gave a soft snort.

"What ice shell?" He looked at Robert. "Chang'e 1 through whatever didn't detect any ice shell, how is that possible?"

Robert seemed to have thought of something and replied, "Guanghan Palace."

Zheng Ming was stunned. "Huh? What Guanghan Palace?"

"Ancient people in China called the Moon Guanghan Palace; 'Han' means cold."

"It's not just China. Ancient Babylonians associated the Moon with cold. In Indian mythology, the Moon is the dwelling place of the cooling god Soma. In Norse mythology, the Moon is ruled by the god of cold."

Zheng Ming frowned. "What does this prove?"

"How did ancient people know the Moon was cold?" Robert looked at him with interest. "Thousands of years ago, in an era without thermometers or detectors, ancient civilizations all over the world coincidentally associated the Moon with cold."

"You could say it's a coincidence. But when there are too many coincidences, it's worth thinking about."

Zheng Ming opened his mouth, unable to speak for a moment.

Celestial Master Zhang was drinking tea, and he couldn't help but click his tongue in wonder.

"In this case, how did the ancients know it was cold on the Moon? Was it pure fantasy, or...?"

As he finished speaking, Wang Chongyang, Celestial Master Zhang, and Zheng Ming all wore expressions of curiosity.

Wang Chongyang asked, "So, it is very reasonable that there is an ice shell on the Moon?"

Robert nodded repeatedly. "Yes, Teacher Wang Chongyang, this is also what the astronomical community believes today."

On the big screen, in the villa living room, Xiao Yu took a deep breath, her eyes full of anticipation.

"Big brother, is there more?"

"Naturally."

"That is, the interior of the Moon might be hollow."