Are there any terms in English, either colloquial or scientific, to describe the highest and lowest points of elevation on a given object (particularly a planet)?
For example, one could say that the deepest point on Earth, the Mariana Trench, is 11,034 meters below sea level, or you could say that Earth's sea level is 11,034 meters above Earth's... what? Similarly, the peak of Mt Everest is 8,848 meters above sea level, which means that Earth's sea level is 8,848 meters below its... what?
This is particularly tricky for other planets, which don't have a sea level as a convenient baseline: "The Martian landing site is at a very high elevation, just 2,000 meters below the summit of Olympus Mons, which is the ________ of Mars."
Do those terms exist? Or do we have to use longer phrases like "highest point" or "greatest elevation"?