Excerpt from the February 15, 1964, issue of Science News Letter
The atmosphere on Mars is as thin as the earthly air 15 miles above the surface, the American Meteorological Society meeting in Los Angeles was told. Martian “air” is mostly nitrogen, with a little carbon dioxide and traces of oxygen and water vapor, unlike that on earth. The Martian atmosphere has now been found to be about a third as dense as previously believed. The finding has forced scientists to revise their designs of capsules that could land on Mars…. A thinner Martian atmosphere means designing a parachute system that will operate at such a low pressure or allowing more weight for retro-rockets to slow the capsule.
All the probes that have landed on Mars have used parachutes to slow in the thin atmosphere. The Soviet Mars 2 lander was first in 1971, but its parachute did not deploy