“For large cosmic objects, energy and gravity conspire to turn objects into spheres. Gravity is the force that serves to collapse matter in all directions, but gravity does not always win—chemical bonds of solid objects are strong. The Himalayas grew against the force of Earth’s gravity because of the resilience of crustal rock”
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“Interplanetary space is so notempty that Earth, during its 30 kilometer-per-secondorbitaljourney,plowsthroughhundredsoftonsofmeteorsperday—most of them no larger than a grain of sand. Nearly all of them burn in Earth’s upper atmosphere,slammingintotheairwithsomuchenergythatthedebrisvaporizes oncontact.”
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“Earth’s atmosphere is commonly described as extending dozens of miles aboveEarth’ssurface.Satellitesin“low”Earthorbittypicallytravelbetweenone hundred and four hundred miles up, completing an orbit in about ninety minutes.”
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