Curiosity

A rover with a question to answer

Curiosity is a NASA rover that landed on Mars in 2012. Its assignment was narrow and specific: to investigate whether conditions at its landing site had been favourable for microbial life, and whether rocks there could preserve clues about possible past life ^[1]. That framing matters. The rover was not sent simply to look for life; it was sent to test whether the environment had ever offered what small organisms would need, and whether the geological record at that place was capable of keeping evidence of them.

Seven minutes and a sky crane

The descent was the difficult part. From the top of the Martian atmosphere to the surface took about seven minutes, a phase NASA engineers called the “Seven Minutes of Terror” ^[3]. During that time the spacecraft steered itself, using S-curve manoeuvres to manage its approach ^[1]. In the final seconds the upper stage of the descent system acted as a sky crane: it lowered the rover on a tether and set it down directly on its wheels ^[1].

NASA chose this arrangement because Curiosity was too big and heavy to land with the airbags used by its predecessors ^[2]. Airbags work by wrapping a smaller rover and letting it bounce; a vehicle of this size needed a different solution, in which the descent stage stays in the air and lowers the rover on a tether instead of dropping it.

The landing was also more accurate than earlier Mars landings. The mission came down within a target area about 20 kilometres long, roughly a five-fold improvement in precision ^[1]. Precision matters because a rover can only study what it can reach.

Where it landed

Curiosity landed on the floor of Gale Crater on 6 August 2012 Universal Time, the evening of 5 August Pacific Time ^[1]. The site, named Bradbury Landing, lies near the foot of a layered mountain, Aeolis Mons, also called Mount Sharp ^[1]. A layered mountain is a stack of sedimentary rocks, which is part of why such a site is worth visiting: the layers record changes in the environment in order, one after another.

Instruments and people

Curiosity carried a science payload more than 10 times as massive as those of earlier Mars rovers ^[1]. More instruments, and larger ones, mean more measurements at each stop, from the chemistry of rocks to the structure of the surface. Behind the machine was a large team: more than 400 scientists from around the world took part in science operations ^[1].

Its place in Mars exploration

Curiosity sits at a transition point in how NASA lands on Mars. Its predecessors arrived inside airbags; Curiosity arrived on a tether from a hovering descent stage, because it was too heavy for the older method ^[2]. And it landed with a precision about five times better than earlier missions ^[1]. Those two points matter together: a heavier payload is what allows a rover to carry the instruments needed to answer a question, and a more accurate landing is what puts the rover where that question can actually be answered.