LOS ANGELES — In three years, a new explorer will touch down on the Red Planet. Wheels churning, machinery whirring, the rover will amble across the rusty terrain, looking for rocks to send back to Earth — rocks that could prove there once was life on Mars.
It is the first time in history scientists have had a real shot at addressing one of humanity’s deepest questions: Are we alone?
But first they must decide where to look.
There are three options: a former hot spring NASA has visited once before, a dried-up river delta that fed into a crater lake, and a network of ancient mesas that may have hidden layers of underground water.
In the coming week, after decades of dreaming, years of research and a heated three-day debate at a workshop in Los Angeles last month, NASA’s top science official will choose which spot to explore. The site he selects will set the stage on which generations of scientists probe the mysteries of our existence.
This rover, scheduled to launch in 2020, is just the first phase of a multibillion-dollar, four-step sample return process. To put pieces of Mars in the hands of scientists will require a lander to retrieve the samples; a probe to bring them home; and then an ultra-secure storage facility that will keep Earth life from contaminating the Mars rocks — and vice versa.
Yet the discovery of fossils in those samples could illuminate the origins of life here on Earth. It could hint at whether someone else is still out there, waiting to be found.
“I want to know,” said Matt Golombek, a NASA scientist charged with guiding the search for a landing site. “Don’t you? I want to know what’s there. I want to know how big an accident we are.”
That hunger for knowledge is what drew hundreds of people to the recent workshop — veteran space explorers and aspiring PhDs, an 18-year-old college freshman and an 80-year-old retired accountant — to assess which plan was best. For days they debated, fueled by curiosity and weak coffee, conscious that the outcome of their meeting could influence NASA and shape history, acutely aware of what they still didn’t know.
So much about Mars remains a mystery. The very notion of alien life is barely more than an educated guess buoyed by wild hope.
They are hopeful.
A search on a failed planet
On Earth, microscopic life is inescapable. Biology began here almost 4 billion years ago, when the planet was still being bombarded by debris left over from the formation of the solar system. Today, tiny, tenacious organisms are splashing in the hot springs of Yellowstone National Park, flying in clouds, freezing in Antarctica, lurking up to a mile and a half beneath the ground.
If it could happen here, why not there?
Mars has been visited by more than two dozen satellites and rovers, which showed it was not always the desert world we see today. Dormant volcanoes and frozen floods of lava demonstrate that the planet once had an active interior that drove tectonic activity. Empty channels, gullies and lakes suggest that liquid water once lapped at the surface — which might mean a thicker atmosphere existed to keep the water from boiling away.
But then disaster struck. Less than a billion years into its history, most experts say, the planet’s molten core stopped churning. This led to the decline of carbon-belching volcanoes and the loss of Mars’s protective magnetic field. Cosmic radiation and energetic particles from the sun stripped away the planet’s atmosphere, causing any water on the surface to evaporate. Goodbye, ocean; so long, lakes; farewell to moist soils and bubbling volcanic vents — all the kinds of places that life likes to live.
Now Mars is seen as a “failed planet,” a frightening alternate-reality version of the world we inhabit.
“It’s Earth where the Earth environments went away,” Bethany Ehlmann, a planetary scientist at Caltech, said at the workshop. “So the question is, why? And when?” And, most momentous of all, “Did life have a chance to get going before then?”
Those questions can be answered only by bringing Mars rocks back to Earth, most scientists say. A human in a top-tier lab would be able to analyze the samples atom by atom, revealing tiny structures a robot couldn’t see.
The detection of even a few ragged molecules left by a microbe would be historic. Knowing that biology arose on two neighboring planets would suggest that life is common throughout the universe. The environment where the Martians are found — be it a hot spring, a river delta or an underground refuge — might provide a clue to where life on Earth originated.
And the knowledge that a world could harbor life and then fail would underscore our own unbelievable good fortune. The conditions for Earthlings’ continued existence may not always be so assured.
“We have to get those samples, and they have to be the right ones,” Golombek said.
In the back of the ballroom, one researcher turned to the person next to her and grinned: “Are you ready for the showdown?”
Columbia Hills: Former hot spring
Option one for the mission is a field of Yellowstone-like hot springs explored by the rover Spirit between 2004 and 2010. Here, beside a rocky outcrop called Home Plate, the now-defunct rover uncovered strange, fingerlike structures made of silica, a mineral associated with water and life. But the rover wasn’t equipped with instruments capable of detecting complex organic compounds, so the mystery of these structures went unsolved.
Seven years later, Spirit instrument operator Steve Ruff received an unlikely epiphany via volcanology journal: Scientists had discovered an otherworldly geyser field in the Andes that contained structures just like the ones on Mars. At the site, called El Tatio, heat-loving microorganisms produce silica deposits in filaments, mats and spires.
“This is the place that is the most Mars-like of any setting I’ve ever been,” Ruff said.
But revisiting a site might mean there’s less to learn, many scientists worry. And what if Ruff is wrong about the silica structures?
Ruff’s only reply: “What if we’re right?”
“If one of the drivers of exploring Mars is to answer this question, ‘Are we alone?’ and we find a place that could address that question and we turn away from it because it’s not guaranteed that we’re going to find it, I think that’s just — ” He paused, searching for a term that wouldn’t offend any of his colleagues. “A conservatism,” he said finally. “And that’s just not characteristic of NASA.”
This site near Mars’s equator was explored between 2004 and 2010 by the rover Spirit.
Jezero Crater: Empty lake
If any version of sending a rover 50 million miles through space can be called “conservative,” landing in Jezero Crater might be it. It most closely resembles the kinds of environments where ancient fossils have been uncovered on Earth: deltas, where sediments from vast watersheds accumulate and are preserved.
“Sedimentary rocks tell us the history of what’s been happening at a site,” said Tim Goudge, a geologist at the University of Texas at Austin. “It’s recorded in the layers, and you can read them like a book.”
Jezero also contains minerals that are associated with life on Earth, such as carbonate, as well as clays called smectites that are known to “entomb” organic material.
But the site is strewn with rippling sand dunes — a potentially fatal hazard for a rover.
“They scare the bejeezus out of me,” said Ray Arvidson, a scientist at Washington University in St. Louis. On a mission to Mars, there are no reboots.
Jezero Crater is the site of an ancient delta that fed into a crater lake.
Northeast Syrtis: Subterranean sanctuary
Ehlmann, the Caltech scientist, has spent years gazing at maps of the mesas at Northeast Syrtis. It’s a distinctly Martian environment, which could be home to uniquely Martian life.
“This would be a chance to go be a geologist there,” she said. “I want to look at the rocks, to understand them, unravel the story they tell.”
The site appeals to many scientists because of the diversity of ancient rocks it contains. Debris from ancient meteorite impacts, called “mega breccias,” would be some of the oldest rocks sampled from any planet in the solar system. Rocks a billion years younger could reveal how Mars became the world it is today.
The area also boasts minerals, like carbonates, that suggest it once harbored an underground aquifer — a potential refuge for organisms seeking protection from their planet’s harsh and erratic climate.
But if subsurface life was sparse, even the most sophisticated laboratory instruments on Earth might not be able to detect it. Scientists are more accustomed to looking for life in sedimentary rocks like those at Jezero.
Then Emily Lakdawalla, a geologist and senior editor for the Planetary Society, posed a question that loomed over every site being considered.
“What if the samples don’t get returned?” she said. “Are we allowed to think about that?”
There was a pause as people contemplated the possibility. NASA has not yet funded any of the three follow-up missions that are required for sample return.
Golombek took the microphone.
“We’ve decided to ground rule that out for this conversation,” he said. “It all depends if you’re an optimist or a pessimist, right?”
For the moment, he urged his colleagues, be optimists.
Northeast Syrtis is a region of volcanic rock that may once have harbored underground water.
‘Incredibly grand exploration’
By the final morning of the workshop, there was no consensus on the best spot to land the rover. Some scientists said their minds changed with every presentation, their opinions ping-ponging as they heard compelling evidence from supporters of each site. Others had become more entrenched in their positions.
But what if they didn’t have to choose?
The mission project science team had conceived an ambitious extended mission centered around a new landing location on the edge of Northeast Syrtis called “Midway,” not far from the rim of Jezero Crater.
It would take hundreds of Martian days — the equivalent of several years on Earth — but the rover could conceivably make its way from one site to the other, obtaining the best samples from both. The traverse would carry the rover across steep mountain ridges, crowded rock fields and perilous windswept terrain.
“This is incredibly grand exploration,” said Ken Williford, deputy project scientist for the mission.
Even by Mars standards, Midway was rife with unknowns. Scientists had not been able to conduct detailed analyses of the rocks it contains, and the proposed 15 mile traverse was at the edge of what could be achieved by a lumbering rover.
There were a lot of ways this could end badly, some worried.
“But,” project scientist Ken Farley countered, “there is more than one way to fail.”
“Personally,” he continued, “I don’t want to fail because we have not been ambitious enough to make the sample cache scientifically worthy.”
The vote was held in hushed silence; there was barely a murmur as the results were projected onto the ballrooms screens. Columbia Hills had received relatively low ratings. But Jezero, Northeast Syrtis and Midway were neck and neck and neck.
In the end, the decision would come down to Thomas Zurbuchen.
As NASA’s associate administrator for science, he oversees more than 100 missions aimed at understanding the solar system and beyond. But of all of those efforts, he said, Mars 2020 is where NASA has the most to lose — and humanity has the most to gain.
“This is the riskiest,” he said of the $2 billion mission. “But suppose everything goes exactly as we hoped. . . . The landing site that I’m the deciding official on will make history.”
Days before he was scheduled to receive his final briefing on the landing site options, Zurbuchen remained undecided. He had attended part of the landing site workshop, but there was still so much to consider: engineers’ safety assessments, the potential for follow-up missions, the need to balance astrobiology research with other scientific questions.
And then there was the vision that filled his mind when he closed his eyes to dream — a consideration that wasn’t financial or scientific, but pure hope. A probe carrying the Mars samples hurtling back toward Earth. Scientists retrieving the cache and getting their first glimpse at the pieces of another planet. The lab where the rocks will be analyzed, the complex instruments that will seek out signs of ancient organisms.
And a science classroom where his future grandchildren sit, reading a textbook that bears the name of the place he chose — a place where humanity learned, for the first time, we have not always been alone.