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.
Callisto is without a doubt the most heavily cratered object in the known solar system. This suggests that the surface is very old and inactive. The largest impact crater on Callisto is known as Valhalla. It is 2,485 miles (4,000 km) in diameter. Another large crater, Asgard, has a diameter of 994 miles (1,600 km).It appears that Callisto's surface has undergone very little change since its formation over four billion years ago.he largest impact crater on Callisto is known as Valhalla. It is 2,485 miles (4,000 km) in diameter. Another large crater, Asgard, has a diameter of 994 miles (1,600 km). It appears that Callisto's surface has undergone very little change since its formation over four billion years ago.