What jobu probably means, is that Mars&#x27; atmosphere is too thin for parachutes to slow a reasonably sized craft down to low speeds (that&#x27;s why MSL&#x27;s landing required additional rocket propulsion [1]). Compare with Earth: Here, the terminal velocity of a reentering capsule is slow enough for parachutes to take over, which in turn slow it down enough for touchdown.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Mars_Science_Laboratory" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Mars_Science_Laboratory</a>