The bottom of the world, where water could pool.
The deepest point of the Hellas impact basin is the lowest place on the entire planet, plunging about 7,152 m below the Martian datum. Down here the atmosphere is compressed to its highest surface pressure anywhere on Mars — high enough, in principle, for liquid water to exist without instantly boiling away.
Claim your plot here →Hellas Planitia is one of the largest impact craters in the solar system, gouged out roughly 4 billion years ago by a massive asteroid. Its floor lies so deep that the vertical drop from the highest volcano to this point exceeds 29 km — the greatest range of elevation on Mars.
Because air pressure rises as you descend, the bottom of Hellas has the thickest air on the planet, about 1,155 pascals. That pressure can climb above the 'triple point' of water, meaning liquid water could momentarily be stable here rather than freezing or boiling instantly — a rare distinction on Mars.
From the Olympus summit to this floor is a drop of over 29 km — Mars's full vertical range.
Its ~7.1 km depth below datum rivals the Mariana Trench's depth below sea level.
The air here is roughly double the pressure found on the Martian mean surface.