Though they were made in , these Apollo 14 astronauts' tracks were easily viewed from a NASA spacecraft in orbit around the moon in tracks highlighted in yellow. The Moon has almost no erosion because it has no atmosphere.
That means it has no wind, it has no weather, and it certainly has no plants. Almost nothing can remove marks on its surface once they are made. The second thing is something called tectonics. Because of tectonics, the surface of Earth is recycled many times throughout its long history. As a result, very few rocks on Earth are as old as the rocks on the Moon. The Moon has not had tectonics for billions of years. The third thing is volcanism. Volcanic flows can cover up impact craters. The structure of large craters is more complex because they collapse, forming terraces, central peaks, central pits, or multiple rings.
Very large impact craters greater than kilometers miles across are called impact basins. What influences the size and shape of a crater? The size and shape of the crater and the amount of material excavated depends on factors such as the velocity and mass of the impacting body and the geology of the surface.
The faster the incoming impactor, the larger the crater. Typically, materials from space hit Earth at about 20 kilometers slightly more than 12 miles per second. Such a high-speed impact produces a crater that is approximately 20 times larger in diameter than the impacting object. Smaller planets have less gravitational "pull" than large planets; impactors will strike at lower speeds.
The greater the mass of the impactor, the greater the size of crater. Craters most often are circular. More elongate craters can be produced if an impactor strikes the surface at a very low angle — less than 20 degrees. How can craters be used to determine the age of a planet or moon?
Scientists record the size and number of impact craters — and how eroded they are — to determine the ages and histories of different planetary surfaces.
Early in the formation of our solar system before 3. As a rule of thumb, older surfaces have been exposed to impacting bodies meteoroids, asteroids, and comets for a longer period of time than younger surfaces. Therefore, older surfaces have more impact craters. Mercury and the Moon are covered with impact craters; their surfaces are very old.
Venus has fewer craters; its surface has been covered recently in the last million years! Much of Earth's surface is recycled through plate tectonic activity and erosion , so Earth also has few craters. Why does the Moon have so many craters while Earth has so few?
On Earth, impact craters are harder to recognize because of weathering and erosion of its surface. The Moon lacks water, an atmosphere, and tectonic activity, three forces that erode Earth's surface and erase all but the most recent impacts.
Essentially, the Moon's surface has not been modified since early in its history, so most of its craters are still visible. Barringer Crater Meteor Crater in Arizona, United States, is a simple crater created when a meter-wide foot-wide iron-rich meteroid struck Earth's surface about 50, years ago — a very recent event to a geologist.
The crater is about 1. Its features, such as the ejecta blanket beyond its rim, are well preserved because of the crater's youth; it has not experienced extensive erosion. Fragments of the Canyon Diablo meteorite were found inside the crater. The Vredefort impact crater, about kilometers 60 miles from Johannesburg, South Africa, was formed just a little over 2 billion years ago.
It is the oldest and largest impact crater recognized on Earth's surface. The crater has been extensively eroded, but is believed to originally have been as much as kilometers miles across. The Chicxulub crater in the Yucatan peninsula, Mexico, is not visible at the surface of the seafloor. Scientists rely on geophysical images for information about its size and shape.
This object was probably several hundred feet across and came in from space at a low angle. Most craters have a pretty characteristic round shape, sometimes surrounded by circular ridges or wrinkles. A few have central peaks, and some have debris scattered around them. The shapes can tell scientists about the size and mass of the impactors and the angle of travel they followed as they smashed into the surface.
The general story of an impact follows a pretty predictable process. First, the impactor rushes toward the surface.
On a world with an atmosphere, the object is heated by friction with the blanket of air. It starts to glow, and if it's heated enough, it may break apart and send showers of debris to the surface. When impactors strike the surface of a world, that sends a shockwave out from the impact site. That shock wave breaks up the surface, cracks rock, melts ice, and digs out a huge bowl-shaped cavity.
The impact sends material spraying out from the site, while the walls of the newly created crater may fall back in on themselves. In very strong impacts, a central peak forms in the bowl of the crater. The surrounding region may get buckled and wrinkled into ring-shaped formations. The floor, walls, central peak, rim, and ejecta the material scattered out from an impact site all tell the tale of the event and how powerful it was. If the incoming rock breaks up, as it usually does, then pieces of the original impactor can be found among the debris.
The Moon isn't the only world with craters dug out by incoming rock and ice. Earth itself was pummeled during the same early bombardment that scarred the Moon. On Earth, most craters have been eroded away or buried by shifting landforms or sea encroachment. Only a few, such as Meteor Crater in Arizona, remain. On other planets, such as Mercury and the surface of Mars , craters are quite obvious, and they haven't been eroded away.
Although Mars may have had a watery past, the craters we see there today are relatively old and still look in fairly good shape. Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance.
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