Continuous positive airway pressure (CPAP) machines are used to maintain an open airway in patients diagnosed with obstructive sleep apnea. The machine functions by blowing pressurized air into the airway via mask at a setting determined by sleep study and prescribed by a physician.
Only around 180 impact craters have ever been discovered on Earth and around 30 per cent of them contain important natural resources of minerals or oil and gas. The largest and oldest known crater prior to this study, the 300 kilometre wide Vredefort crater in South Africa, is 2 billion years in age and heavily eroded.
The largest craters on the Moon, like Mare Imbrium which is over 1100 km in diameter, have been flooded by lava and we can only see parts of their circular outline. Because these dark mare (which means 'sea') have few craters on them, they must be younger that the surrounding areas. Simple craters like Moltke (which is 6.5 km in diameter and 1.3 km deep), have a smooth bowl-like shape with smooth walls. Most small craters less than about 15 km in diameter are simple craters.