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Narrator: If you wanted to learn more about the history of the Earth and other rocky

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planets in the solar system, where would you look? For years, scientists have turned to

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one of the solar system's most common features: Impact craters. Left over

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from earlier periods of our planet's history, these sometimes giant holes in the surface can

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teach us about the Earth based on how they've changed over time. However, since even the newest

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impact craters on the Earth have changed due to wind, rain, snow, and even

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lakes filling them, we need to compare them to a fresh crater that still looks like it did when it was

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first created. So where exactly can scientists find a crater like this? Certainly

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not on Earth, but there's one on the Moon that's just about perfect. The Linné Crater,

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a small impact crater located in the western Mare Serenitatis, is extremely young,

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and scientists have always thought that it might be a great example to use to compare with other craters.

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Now, thanks to high-resolution, three-dimensional data generated from NASA's

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Lunar Reconnaissance Orbiter, scientists are sure of it. So why use a crater

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on the Moon, and why this specific example? Unlike craters on Earth--and even

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Mars--many Moon craters are well-preserved because they erode much more slowly.

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However, despite that, not all Moon craters are ideal for comparison.

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After a crater is first formed, it can be impacted again and again by other objects,

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which modify its original shape. This is why scientists have been looking for a crater

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that's not so beaten up, and one that preserves all the telltale signs of how impact cratering

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works. The Linné Crater fits the bill perfectly. By looking at

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data from LRO's LROC instrument, scientists have confirmed that it has remained largely

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untouched aside from normal wear and tear, which is what makes it so perfect for comparison.

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They've also discovered some interesting and unexpected things. For decades,

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lunar scientists counted on the simplest craters, like Linné, as being bowl-shaped.

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However, thanks to the new data, scientists have discovered that they actually resemble

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an upside-down cone. This, along with other findings, sheds new light not

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only on Linné Crater, but also on the evolution of similar craters on the Earth, Moon,

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and other planets, allowing us to get a better picture of our own history. In fact,

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the simple shape of Linné, and the way large boulders are strewn around its rim, are

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the basic tools of "forensic geology" that allow scientists to understand how craters started

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out on the Earth and Mars before water and wind wear them away. Without craters

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like Linné on the Moon, we wouldn't know how landforms evolve over time in the presence of weather,

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climate change, and other factors. And all by looking at what initially

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appears to be just another hole in the ground.

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[beeping]

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[beeping, silence]