When NASA's Mars rover Perseverance, a robotic astrobiology lab packed inside a space capsule, hits the final stretch of its seven-month journey from Earth some time tomorrow, it is set to emit a radio alert as it streaks into the thin Martian atmosphere.

By the time that signal reaches mission managers some 127 million miles (204 million km) away at the Jet Propulsion Laboratory (JPL) near Los Angeles, Perseverance will already have landed on the Red Planet - hopefully in one piece. 

The six-wheeled rover is expected to take seven minutes to descend from the top of the Martian atmosphere to the planet's surface in less time than the 11-minute-plus radio transmission to Earth.

Thus, tomorrow's final, self-guided descent of the rover spacecraft is set to occur during a white-knuckled interval that JPL engineers affectionately refer to as the "seven minutes of terror." 

The mission's first hurdle after a 293-million-mile (472-million-km) flight from Earth is delivering the rover intact to the floor of Jerezo Crater, a 28-mile-wide (45-km-wide) expanse that scientists believe may harbor a rich trove of fossilized microorganisms. 

Erisa Stilley, systems engineer on the JPL descent and landing team, described in detail the critical part of the $2.7 billion mission. 

"Once Perseverance has a better sense of where she's at, she then uses a second on board map based on where we can currently divert to at that point in time, and searches that area to find the safest place that she can fly to," she explained. 

"So Perseverance chooses that target and then, and that all happens in the 2.4 seconds it takes for Perseverance to send commands for us to separate from the back shell and start a freefall." 

Much is riding on the outcome. Building on discoveries of nearly 20 U.S. outings to Mars dating back to Mariner 4's 1965 flyby, Perseverance may set the stage for scientists to conclusively show whether life has existed beyond Earth, while paving the way for eventual human missions to the fourth planet from the sun.

A safe landing, as always, comes first. If all goes to plan, NASA's team would receive a follow-up radio signal shortly before 1 p.m. Pacific time confirming that Perseverance landed on Martian soil at the edge of an ancient, long-vanished river delta and lake bed. 

From there, the nuclear battery-powered rover, roughly the size of a small SUV, will embark on the primary objective of its two-year mission, engaging a complex suite of instruments in the search for signs of microbial life that may have flourished on Mars billions of years ago. 

Advanced power tools will drill samples from Martian rock and seal them into cigar-sized tubes for eventual return to Earth for further analysis - the first such specimens ever collected by humankind from the surface of another planet. 

Another experiment is a device to extract pure oxygen from carbon dioxide in the Martian atmosphere, a tool that could prove invaluable for future human life support on Mars and for producing rocket propellant to fly astronauts home. 

Perseverance, the fifth and by far most sophisticated rover vehicle NASA has sent to Mars since Sojourner in 1997, also incorporates several pioneering features not directly related to astrobiology. 

Courtesy: NASA JPL