“We have one data point for life on a planet,” said planetary geologist Bethany Ehlmann of the California Institute of Technology, part of the science team for Perseverance. “Mars is the second data point. We know from the investments that we’ve made from exploration that there was this habitable world right next door. Right about the time that Earth was developing its life, Mars was also habitable, with lakes and rivers.”
A close match between ancient Martian life and life here on Earth would suggest a common origin, with one planet seeding the other through meteorites. Or perhaps Mars had life-forms of a completely alien nature. Or maybe they never existed and Mars has always been a sterile world.
“Is it a foregone conclusion that as long as you have the right mix, things are going to happen and you’re going to end up with life?” said Mary Voytek, head of NASA’s astrobiology program. “We don’t really have the answer to that.”
The new rover mission is officially known as Mars 2020, and it is the first part of a multiphase project called the Mars Sample Return campaign. Only this leg has been fully funded by Congress.
Perseverance will launch from Florida’s Cape Canaveral atop an Atlas V rocket. It will be the second robotic mission to Mars in the span of a week: China on Thursday launched its own probe, named Tianwen-1, which is that country’s first attempt to land a craft on Mars.
While coping with additional challenges introduced by the coronavirus pandemic, NASA has been racing against a deadline imposed by physics: There’s a narrow window when the Earth and Mars are properly positioned in their orbits. Perseverance must launch by Aug. 15, after which the effort would have to be put on hold for a couple of years. It is slated to land on Mars on Feb. 18.
The engineering demands of any robotic mission are enormous. Perseverance will have to descend to the surface of Mars in the notoriously confounding atmosphere — it’s too thin to be very helpful with braking, but just thick enough to cause aerodynamic trouble — and land in one piece, upright and functional. That is not an uncontested layup.
The mission will benefit from autonomous navigation sensors that should allow a pinpoint landing in Jezero Crater, where a river delta once flowed into a deep lake — a site painstakingly selected by scientists as the kind of place that might host remnants of ancient organisms.
Perseverance is being described by NASA as part of its long-term plan for a human mission to Mars. The rover carries an instrument that can manufacture oxygen out of Mars’ carbon dioxide-rich atmosphere, a process critical to future human missions. The rover also carries a small helicopter, named Ingenuity, which will perform the first rotorcraft flight on another planet.
A geologist's dream world
Life as we know it here on Earth is both astonishing in its complexity and strangely ordinary. The simplest organism has a fairly elaborate genetic code. At the same time, it is built with some of the most common elements in the universe, such as hydrogen, nitrogen, carbon and oxygen.
Their search is complicated by the lack of a watertight definition of life. It’s clearly something that chemistry can achieve given the right conditions. A living thing is self-sustaining and structurally coherent. It obtains energy from the world and does something with it. It contains the code of information that allows it to replicate, and does so with enough inexactitude to allow natural selection to work its wonders.
The quest to understand its origin on Earth is also made more challenging by the fact that this isn’t the planet it used to be. The Earth’s surface has been buried, melted, metamorphosed, eroded, crushed, frozen and flooded. There aren’t that many old rocks around.
Mars, by contrast, is a geologist’s dream world. Unlike Earth, Mars lacks plate tectonics. As a result, the Martian surface hasn’t been radically altered over the past 4 billion years the way Earth’s has.
“Those rocks still exist where they were deposited with no complicated overprinting,” Ehlmann said.
Even if the mission doesn’t find signs of life, it might detect “some kind of prebiotic phase of life,” said Benjamin Weiss, a Massachusetts Institute of Technology professor who is part of the Perseverance science team.
“If we could bring back a fossil record, a rock record, some kind of geological samples, that have some record of that prebiotic phase of the evolution of life, that would arguably be as exciting, or arguably more exciting, than finding life,” Weiss said.
Mars has a knack for fooling human beings, especially those eager to discover Martian life. In the late 19th century, astronomer Percival Lowell famously claimed to see canals on Mars, which he posited as the handiwork of a civilization struggling with the drying out of the planet. That notion helped inspire H.G. Wells’s “The War of the Worlds,” the canonical alien-invasion tale.
The canals were, of course, imaginary, but well into the 20th century, some scientists thought Mars might be showing signs of seasonal vegetation. Then came the Space Age, and the first robotic probe to fly by Mars, Mariner 4 in 1965, captured images of a cratered and parched landscape.
NASA’s extraordinary Viking mission put two robotic landers on the planet in 1976 and performed several life-detection experiments. One result looked positive and briefly generated euphoria among the scientists, but when all the data came in, the consensus was that the experiments hadn’t found signs of life.
The field of astrobiology received a boost in 1996, when scientists announced they had found what looked like fossilized microorganisms in a Mars rock discovered in Antarctica after striking the Earth as a meteorite. The rock, scientists said, had been blasted off Mars and into space by an asteroid impact.
The Mars rock generated tremendous media attention, but the microfossils discovery did not age well. Although never fully resolved — there are partisans on both sides of the issue — the consensus is that intriguing features in the Mars rock (officially ALH84001) could be produced non-biologically.
“We learned a really hard lesson in 1996,” said NASA’s Voytek.
Thomas Zurbuchen, the head of science at NASA, said the findings from Martian meteorites that land on Earth are inherently enigmatic, because they have been heated when ejected from Mars and lack the kind of geological context that scientists need.
“Clearly those rocks do not answer the questions that we have. They don’t have the context and they don’t have the careful handling that it takes to make the sample valuable,” Zurbuchen said.
Perseverance is an SUV-size rover that looks like a fraternal twin of Curiosity, the NASA rover that is still exploring the planet. Among other achievements, Curiosity discovered organic molecules in 3-billion-year-old mudstones, although such carbon-based molecules could have a non-biological origin. Perseverance has different tools, including new high-resolution cameras and other remote-sensing instruments.
A discovery of life beyond Earth, even in fossil form, would be so significant that scientists want to make sure they get it right. That’s one reason they want to see Mars samples up close, back on Earth, in facilities where the material can be studied for decades to come.
Finding the best samples
Perseverance is equipped with a drill and 31 canisters. After scouting out the most inviting sites, aided by aerial surveillance from the helicopter, the rover will drill into the surface, put Martian soil and rock cores into the canisters, and then leave them scattered around the planet’s surface the way Hansel and Gretel dropped bread crumbs so they wouldn’t get lost in the woods.
A subsequent rover would then collect them in 2026 and put them into a launch vehicle to be blasted into orbit around Mars. They would then be transferred to an orbiting spacecraft, which would carry the material back to Earth in 2031, under current NASA plans.
Given the project’s complexity, it is critical that the rover pick the right samples, said Abigail Allwood, a geologist at NASA’s Jet Propulsion Laboratory and the lead scientist for one of the rover’s remote-sensing instruments.
The exact itinerary — where the rover will drill and when — remains undetermined. Allwood said she hopes there is abundant time to study the environment first.
“As a geologist, I know the importance of time in the field, looking at the rocks. The more time you spend looking at the rocks, the better you’re going to understand any potential biosignatures,” Allwood said.
She makes a field geologist’s point about what such life would look like: multiplicative. Life copies itself.
“If it’s life, it would not be just one. It will be multiple examples of whatever you are looking at,” she said.