It depends - any atmosphere is a huge boon as long as your spacecraft can do aerobraking in any form. You can use it to change your orbit, capture into orbit fr

It depends - any atmosphere is a huge boon as long as your spacecraft can do aerobraking in any form. You can use it to change your orbit, capture into orbit from an interplanetary trajectory or even change the plane of your orbit as it was envisioned for some mission profiles of the Space shuttle or Dyna-Soar. There are nice tables at Project RHO illustration how much delta-v you can save by aerobreaking when traveling between Solar System bodies: http://www.projectrho.com/public_html/rocket/appmissiontable.php http://www.projectrho.com/public_html/rocket/appmissiontable... You loose all of that for an airless body like the Moon. In this case it's not that big of an issue as moon is close & has a low gravity. If Mars was airless, it could be much more of an issue, as you are coming much more quickly from an interplanetary trajectory & there would be more gravity to handle during landing than on the Moon.