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Update 2/18/21 @ 4:05pm EST: Perseverance landed on Mars’ surface successfully and captured two images of the Red Planet.

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Practice makes perfect, and NASA will hope for both practice and perfection as it attempts to land its latest rover, Perseverance, on the surface of Mars later today. If it succeeds, Perseverance will mark NASA’s sixth consecutive successful touch down on the Red Planet. If it fails, it will be the agency’s first crash landing in 22 years.

As a Rube Goldberg-esque series of contraptions tries to safely slow the one-ton science laboratory—currently screaming through space at more than 12,000 miles per hour—to a gentle halt on the ground, the landing will unfold nearly live. Tune in at 2:15pm Eastern on any one of a handful of video streaming platforms to watch (in English or in Spanish) the rover end its interplanetary journey with a first-of-its-kind landing, and hopefully begin its scientific mission: hunting for signs of ancient alien life.

Perseverance blasted off from Cape Canaveral about seven months ago, the last of a convoy of spacecraft taking advantage of the once-every-two-years window for efficient paths from Earth to Mars. It is also the last of three crafts to reach the planet, after an orbiter called Hope from the United Arab Emirates and a Chinese probe, Tienwen-1.

While the SUV-sized vehicle looks nearly identical to its predecessor, Curiosity, which is currently celebrating its tenth (Earth) year of operations on Mars, the Perseverance mission represents the culmination of a decades-long astrobiology program aiming to answer one fundamental question: did alien life ever live on the Red Planet?

NASA has nearly found signs of microbial life on Mars twice before. When the twin Viking landers attempted to grow any theoretical bacteria that might have been living in the Martian soil and look for signs of their activity in the 1970s, the instruments reported conflicting results. They saw whiffs of carbon from possible alien digestion, but without the organic molecules expected to form organisms. Then in 1996, researchers spotted crystalline shapes in a Martian meteorite that they believed could have been sculpted only by life. Other researchers found possible non-biological origins. A few scientists continued to dispute the interpretations of both observations, but one lesson was clear. Planetary scientists would have to work out how chemicals, gases, and minerals mix on Mars in much greater detail before astrobiologists could hope to recognize the subtle signs of life.

Through the traipsings of a veritable fleet of wheeled vehicles of increasing complexity, including Sojourner, Spirit and Opportunity, and Curiosity, NASA has completed many of its Martian geology and chemistry prerequisites. Now, it’s ready to attack the final exam: Martian biology, with Perseverance’s suite of sophisticated instruments. Its combined senses will search for the most general indications of life that researchers have been able to come up with—molecules clumped together in patterns unlikely to have arisen in other ways. The probe will also collect the first samples of Mars (to be returned by a future mission), test a prototype machine for producing oxygen from the thin Martian atmosphere, and deploy the first extraterrestrial helicopter.

To search for what amounts to fossilized leavings of ancient life, astrobiologists have selected Jezero Crater, a basin where the water from various rivers pooled more than 3.5 billion years ago. The site’s range of rocks and sediments from different eras and locations has long intrigued researchers. Some scientists had proposed landing Curiosity there, but its scientifically diverse features also made it a logistical nightmare. “In the middle is a steep cliff that runs through the center, and on the outer edges, there’s a rock field, the kind you might see at the bottom of a mountain,” says Swati Mohan, Perseverance’s Guidance, Navigation, and Control Operations Lead.

Mission planners were able to greenlight dropping the $2.7 billion-dollar vehicle into the middle of Jezero Crater’s many hazards largely because a new technology developed just for this purpose: NASA has equipped the spacecraft with eyes, knowledge of the terrain it’s headed for, and the brains to autonomously select its own landing site with more flexibility than any previous lander.

After the spacecraft carrying Perseverance hits the atmosphere, most of the descent will unfold just as Curiosity’s did. First, a parachute will unfurl, taking the vehicle from a supersonic speed down to 200 miles per hour. After the parachute falls away, the spacecraft will fire up a set of downward pointing rockets to further slow its roll. Finally, a nearly-hovering “skycrane” will, if all goes according to plan, lower Perseverance down to the surface. NASA has dubbed the journey from the upper atmosphere to the surface the “seven minutes of terror,” because when the control room gets the signal that the descent has begun, the lightspeed delay between Earth and Mars means that Perseverance will already be resting on the ground, one way or another.

An artist's interpretation of Perseverance, NASA's newest Mars rover, parachuting down from orbit.
Perseverance will parachute down to the red planet before firing rockets to slow itself down. NASA/JPL-Caltech

If the vehicle makes it to Jezero Crater in one piece, that success will be in part due to a new capability that operates only during the 20 seconds after the parachute detaches. At this point in 2011, Curiosity could choose only to go left or right to escape the parachute, based on the wind. But this time around, Perseverance’s cameras will be snapping pictures of the ground, while onboard hardware compares them to stored maps of the surface and searches for the safest possible place to land. For Perseverance, that means it can jet up to four tenths of a mile as it scouts for a particular spot away from slippery slopes, treacherous boulder fields, or sticky sand traps.

While you never know what Mars is going to throw at you, NASA’s confidence in Perseverance’s intricately choreographed landing procedure is high. It worked for Curiosity, and this new “Vision Lander System” has been thoroughly tested, including out in the field in 2019. “To really humble ourselves and make sure we didn’t miss anything,” Mohan says, “we took it out to Death Valley and flew it over terrain that looked like Mars.”

She adds that NASA has run many digital touchdowns in a Mars simulator, which calculates how the landing might play out if it has to contend with gusty winds, swirling dust, blindingly bright conditions, or if the spacecraft has the misfortune of landing on, say, a three-foot wide rock. The Vision Lander System can spot and avoid patches of threatening terrain 18-feet wide, but can’t see objects smaller than that. Curiosity would have had just an 86 percent chance at a safe landing in Jezero Crater, Mohan says, but Perseverance’s eyes and brain bump those odds up to an estimated 99 percent.

Regardless, Mohan and her colleagues will get just one shot to bring the real Perseverance down. Today, they’re hoping that all their practice pays off.

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