After enduring seven minutes of terror, NASA's $2.5 billion rover is already finding proof that the Red Planet was once hospitable to life. 

By Andrew Grant

Illustrations by Ron Miller

Images courtesy of NASA

The spacecraft transporting the Curiosity rover entered the Martian atmosphere at 1:10 a.m. EDT on August 6 after an eight-month journey. Because it takes 14 minutes to send or receive a signal from Mars, NASA operators could not communicate with the craft during its descent; they had to hope that their meticulously plotted engineering and software would, within "seven minutes of terror," slow the probe down from 13,000 miles per hour and gently and precisely deposit Curiosity at the selected landing site.

Friction with Mars's tenuous atmosphere slowed the spacecraft as it descended but created temperatures up to 3,800 degrees Fahrenheit. A heat shield protected the rover inside from incineration. Meanwhile, a network of eight thrusters adjusted the trajectory toward the landing site. At an altitude of about seven miles, with Curiosity traveling at 900 miles per hour, a 50-foot-wide parachute deployed. Twenty-four seconds later, the probe ditched its heat shield and checked speed and altitude using onboard radar.

Just one mile before touchdown, the spacecraft played its trump card: Audacity, a rocket-powered platform designed specifically to shuttle Curiosity to the Martian surface. (Previous Mars rovers had landed with air bags, but the one-ton Curiosity was far too porky for that approach.) Audacity used eight engines to slow to a leisurely 1.7 miles per hour as the rover, connected by a bridle, dangled beneath. Audacity kept dropping until it sensed the rover was stable on the ground. Then it cut itself loose, throttled up its rockets, and flung itself skyward, crash-landing 2,100 feet away. Curiosity arrived in perfect shape, ready to get to work.

One of Curiosity's first photos was a black-and-white look at its landing site, Gale Crater. In the distance was Mount Sharp, a stratified, 18,000-foot peak that should show how environmental conditions on Mars have changed over time.

Curiosity arrived bristling with geology tools, two of which it tested on a football-size rock nicknamed Jake.

The rover's ChemCam blasted Jake with a laser (red dots), while its Alpha Particle X-Ray Spectrometer bombarded the rock with radiation (purple circles). The instruments revealed that Jake is a basaltic rock similar to those found in Hawaii.

In September Curiosity found an outcrop of conglomerate rock, pebbles and gravel bound together by wet sediment. After years of inferring the existence of ancient water from chemical analyses and satellite photos, this is by far the most direct proof that water once flowed on Mars. Scientists estimate that 4 billion years ago a river up to a few feet deep lazily flowed down from Gale Crater's rim. Curiosity's next task is to determine whether other conditions on ancient Mars, like the chemistry of the soil and air, were also favorable to the development of microbial life.