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Itis_TheStranger t1_j96jwv0 wrote

That's beautiful.

Why do other planets, and moons have so many visible crater impacts? Earth doesn't have very many compared to Mars, or our moon.

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djh_van t1_j96ljrc wrote

  • Our atmosphere protects us from a lot of the small and medium impacts by burning them up. Other celestial objects have either no atmosphere to do this (moon) or a very thin atmosphere that doesn't burn them up before impact (mars), or the wrong composition of atmosphere.

  • Often they don't have a climate to weather the impact craters that were made.

  • our moon acts like a giant magnet or deflector shield orbiting our planet and scoops up a lot of the objects that might otherwise have hit us.

  • the gravity of some of the bigger planets (Jupiter, Saturn) actually helps to deflect some of the more energetic objects coming from outside our solar system

  • the old impact craters are there, but they are ancient and our planet's life has covered them with vegetation and millenia of human activity.

  • and lastly, we've been very very very lucky in the last few hundred years. Nothing major has got through that obstacle course. But in recorded human history there have been a few biggies get through. Ancient records describe them, and even as recently as during the explorer days we've had records of asteroids coming in over some remote island or oceans.

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OlympusMons94 t1_j96r48u wrote

Atmospheric composition doesn't matter. Density does some for small objects, but any rock big enough to make the large craters visible in images like this won't be stopped by an atmosphere.

The Moon provides negligible shielding. It covers only a tiny portion of the sky. Hold out your little finger at arm's length. The Moon is half as wide (that's wide, not long) in the sky as that little finger. Imagine how good a shield that tip of your little finger would be. Well, the Moon is smaller and it's not at arm's length. It's almost 400,000 km away. Ther eis a lot of room in between.

Earth is also a much bigger target with much stronger gravity compared to the Moon.

Jupiter is about as likely to send objects toward Earth as divert them away.

Weathering, erosion, and covering with water and sediment (as well as vegetation) because of our thick atmosphere and water are important.

Besides that, Earth has a lot of volcanism to resurface face cratered areas. That is also why the dark lunar maria we can see on the Moon are so lightly cratered compared to the lighter surrounding highlands. The maria are giant plains of frozen lava. (Much of the maria surfaces are still really old, though. A relate dlld point is that there were a lot more eimpacts very early in the solar system's history.)

Lastly, Earth also has active plate tectonics, which deforms craters on land, completely subducts craters on the ocean floor within a couple hundred million years, and is related to Earth's volcanic activity.

Because of geologic activity, Venus, Europa, Enceladus, Io, and Pluto all have surfaces with few large or obvious craters. Their surfaces have all been resurfaced by lava or ice within the past few hundred million years.

u/Itis_TheStranger

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Itis_TheStranger t1_j97jdbx wrote

Thank you for that reply. This is a great conversation and it's interesting to read the different information.

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vipperofvipp t1_j97qhlj wrote

I’ve read a description before of Jupiter being described as a massive offensive lineman that protects Earth.

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rocketsocks t1_j976b13 wrote

Erosion, water and the atmosphere. The atmosphere protects the surface from some impacts, causing a larger number of small sized impactors to blow up in the air before reaching the surface and forming a crater. A similar effect happens with smaller impactors that hit the ocean and aren't large enough to make a crater in the ocean floor. The big factor though is erosion and plate tectonics. If you look at the surface of Mars most of that crust is ancient, billions of years old. On Earth the crust gets recycled constantly due to tectonics and volcanism. The big island of Hawai'i is a fraction of a million years old, for example, and the ocean floor keeps getting recycled in a process that keeps most of it under 150 million years old.

Then you have erosional processes due to the air, the water cycle, life, etc. Mountains get worn down, surface features get changed by rivers and shorelines, rocks get changed and moved around, life covers up or erodes surface features, etc. There's a huge crater in the Yucatan peninsula from the impactor that ended the reign of the dinosaurs 66 million years ago, but it's not easily visible to the naked eye because of all the erosional processes that have occurred since then. Remnants of older craters have been found but they are also not easily visible because of erosion. Smaller craters have a tendency to get completely erased by geological activity and erosion.

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Extreme_Track1n t1_j97in53 wrote

Earth has been hit by even more impacts than Mars has but because Earth has a thick atmosphere and strong weather systems the impact craters get weathered down until they are no longer visible or the the objects burn up in the atmosphere before hitting the ground.

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[deleted] t1_j96kl15 wrote

[deleted]

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kerfitten1234 t1_j96viy6 wrote

No, it's because of erosion and the fact that earth is tectonically active. Any meteor large enough to leave a decent crater isn't going to be stopped by an atmosphere.

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[deleted] t1_j96z3xq wrote

[deleted]

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kerfitten1234 t1_j970pm4 wrote

Lol, your source is an opinion piece meant for kids.

https://www.britannica.com/science/meteorite-crater/The-impact-cratering-process

>Earth’s atmosphere certainly slows and prevents typical asteroidal fragments up to a few tens of metres across from reaching the surface and forming a true hypervelocity impact crater, but kilometre-scale objects of the kind that created the smallest telescopically visible craters on the Moon are not significantly slowed by Earth’s atmosphere...

The atmosphere shielding the surface is not the reason for that lack of craters on earth.

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Itis_TheStranger t1_j96l9zk wrote

Thanks for that explanation. I kinda figured it had something to do with the atmosphere. I know there are some impact craters on earth, but they are usually larger.

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