More Mars landing attempts have failed than on any other planet or moon due to one fundamental physical property of Mars. That property is the atmosphere. This is the reality NASA will face Monday November 26^th 2018 and every time they land on Mars. The Martian atmosphere is just thick enough to burn up a space craft but too thin to slow it down for a soft landing. For landing a space craft it is the opposite of a Goldilocks zone. Let us compare Mars to the planets and moons we have landed on to see why that is the case.

Consider the Moon. 

It has no atmosphere.  Since it has no atmosphere when we try to land on it there is no frictional atmospheric heating.  No heat shield is required.  No having to worry about parachutes deploying.  On the downside, no atmosphere is that nothing will slow down a space craft that lands on an airless body like the Moon. So descent thrusters are required on the Moon.  This means problems and complications of rocket engines on landing.

Consider Earth, Venus, and Titan (a moon of Saturn). 

These three bodies have in common atmospheres that are at least as thick as the atmosphere on Earth, in fact Venus and Titan have thicker denser atmospheres than Earths.   Therefore, it is possible to land with parachutes only.  Even on a hard surface landing that are soft enough for probes to survive are possible.  Human crews need a bit more cushion so a splashdown on Earth or a brief blast with much smaller simpler landing rockets are employed.   The downside of a thick atmosphere is that it can burn you up as we were all reminded of when Shuttle Columbia was destroyed on reentry.    That said we know many safe ways to land a space craft on Earth and in similarly thick atmospheres.

Mars Atmosphere, The Deathlylocks Zone. 

Mars atmosphere is not too thick to provide enough braking to slow down a space craft and land.  Mars atmosphere is not too thin to require no parachutes and make you depend on rockets completely.   Just about as thin as the atmosphere of Earth 6-10 miles up. The Martian atmosphere is just right. 

Just right to be thick enough to burn a space craft to a crisp and thin enough that parachutes and rockets are required to land anything of significant mass.  (Otherwise, the airbag system NASA used could be employed, but that system has certain limitations and complications comparable to rocket power).     

Surely, we all know what a goldilocks zone is.  A set of natural conditions that are just right.    The Martian atmosphere is, for landing space craft, a deathlylocks zone.  Landing on Mars presents a set of natural conditions that make things as difficult as possible.

To land on Mars a space craft must have both the complicated processes of deploying parachutes at high velocity go off perfectly.  At almost the same time the complex processes of deploying rockets must go perfectly within minutes or seconds.   If just one part of that goes wrong the mission will fail.

Random strangely related thoughts.

Landings on other planets are always interesting. I do want to mention in a positive way a enterprise I used this blog to castigate. Cruncyroll.com has finally done right by the transgender community. It always bothers me when media sources are much more strident in criticism and silent in praise. So since I'd randomly mention them at the end of other articles I mention them here.

It is the nature of news for good things to gets less print.

Along those lines ... hopefully there will be nothing much to write about tomorrow since safe landings aren't news in the way that crashes are.