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LOS ANGELES – In three years, a new explorer will land on the red planet. The wheels turn, the machines purr, the rover will crisscross the rusty terrain in search of rocks to send back to Earth – rocks that could prove it was life on Mars.
This is the first time in history that scientists really have the opportunity to answer one of the most profound questions of humanity: are we alone?
First, they must decide where to look.
There are three options: an ancient hot spring NASA once visited, a dry river delta feeding a crater lake, and a network of ancient mesas that may contain layers of underground water.
Next week, after decades of dreams, years of research and a three-day debate at a workshop in Los Angeles last month, NASA's top scientist will choose the place to explore. The site he chooses will pave the way for generations of scientists exploring the mysteries of our existence.
The discovery of fossils could shed light on the origins of life on Earth. This could indicate if anyone is there, waiting to be found.
"I want to know," said Matt Golombek, a NASA scientist responsible for guiding the search for a landing site. "Are not you? I want to know what is there. I want to know how bad we are.
This thirst for knowledge is what has attracted hundreds of people in the recent workshop – space explorers and aspiring PhD students, doctoral student, 18-year-old college freshman and 80-year-old retired accountant – to determine which plan was the best. For days, they debated, stimulated by the curiosity and weakness of coffee, aware that the results of their meeting could influence NASA and shape the story, aware of what they did not know.
So much about Mars remains a mystery. The very notion of extraterrestrial life is little more than an enlightened conjecture carried by wild hope.
They are full of hope.
Why not there
On Earth, microscopic life is inevitable. Biology started here nearly 4 billion years ago, when the planet was bombarded by debris left behind by the formation of the solar system. Today, tiny, tenacious organisms are frolicking in the hot springs of Yellowstone National Park, flying in the clouds, freezing in Antarctica, hiding up to a mile and a half underground.
If it could happen here, why not here?
Mars was visited by more than two dozen satellites and rovers, which showed that it was not always the desert world we see today. Sleeping volcanoes and frozen lava floods demonstrate that the planet once had an active interior, conducive to tectonic activity. Channels, gullies and empty lakes suggest that a liquid water has already sunk to the surface – which could mean a thicker atmosphere to prevent water from boiling.
Then the disaster hit. According to most experts, less than a billion years in its history, the molten nucleus of the planet has stopped turning. This led to the decline of volcanoes at the carbon attack and the loss of the protective magnetic field of Mars. Cosmic radiation and energy particles from the sun have destroyed the planet's atmosphere, causing all surface water to evaporate. Goodbye, ocean; so long, the lakes; goodbye wet soils and bubbling volcanic chimneys – all types of places that life loves to live.
Mars is considered a "failing planet," a frightening version of alternative reality in the world in which we live.
"It's the Earth where the Earth's environments are gone," Bethany Ehlmann, scientist in planetary science at Caltech, told the workshop. "So the question is why, and when?" And, most important of all, "Did life have a chance to leave before?"
Most scientists have answered these questions by bringing the rocks of Mars back to Earth. A human in a leading laboratory would be able to analyze the samples atom by atom, thus revealing tiny structures that a robot could not see.
The detection of some ragged molecules left by a microbe would be historic.
Knowing that biology was born on two neighboring planets, this would suggest that life is common throughout the universe. The environment where the Martians are – whether it's a hot spring, a river delta or an underground shelter – could provide a clue on the origin of life on Earth.
To know that a world could harbor life and then fail would emphasize our incredible luck. The conditions for the survival of landlords are not always so secure.
"We have to get these samples and they have to be the right ones," Golombek said.
At the back of the ballroom, a researcher turned to the person next to her and smiled: "Are you ready for the confrontation?"
Silica structures
The first option for the mission is a field of hot springs resembling Yellowstone explored by the Spirit rover between 2004 and 2010. Here, next to a rocky outcrop called Home Plate, the deceased rover has unearthed some strange Finger-like structures in silica, a mineral associated with water and life.
The rover was not equipped with instruments capable of detecting complex organic compounds, so the mystery of these structures has not been solved.
Seven years later, Steve Ruff, Spirit instruments operator, received an unlikely epiphany via a volcanology journal: scientists had discovered a field of geysers from another world in the Andes, which contained similar structures to those of Mars. At the site, called El Tatio, heat-loving microorganisms produce silica deposits in the filaments, mats and arrows.
"It's the most Mars-like place of all the contexts I've ever been," said Ruff.
Revisiting a site may mean that there is less to learn, many scientists fear. What happens if Ruff is wrong about the silica structures?
Ruff's answer: "What if we're right?"
"If one of the engines of Mars exploration is to answer the following question:" Are we alone? "And if we find a place that can answer this question, we turn away from it because it's not guaranteed we'll find it, I think it's just …" He paused, looking for a term. "A conservatism," he finally says. "And that's just not characteristic of NASA."
Jezero Crater
If one can qualify as "conservative" sending a mobile within a radius of 50 million kilometers, he could land at Jezero Crater.
It most closely resembles the kind of environment where ancient fossils have been discovered on Earth: the deltas, where sediments from large watersheds accumulate and are preserved.
"Sedimentary rocks tell us the story of what's happening on a site," said Tim Goudge, a geologist at the University of Texas at Austin. "It's saved in layers and you can read them as a book."
Jezero contains minerals associated with life on Earth, such as carbonate, as well as clays called smectites, known to "bury" organic matter.
The site is dotted with sand dunes – a potentially deadly danger for a rover.
"They scare the bejeezus from me," said Ray Arvidson, a scientist at Washington University in St. Louis. On a mission to Mars, there is no restart.
Diversity of rocks
Ehlmann, scientist Caltech, spent years looking at the maps of the mesas north-east of Syrtis. It is a typical Martian environment, which could house a typical Martian life.
"It would be a chance to be a geologist," she said. "I want to look at the rocks, understand them, unravel the story they're telling."
The site appeals to many scientists because of the diversity of ancient rocks it contains.
The remains of ancient meteorite impacts, called mega breaches, are believed to be among the oldest sampled rocks of all planets in the solar system. Rocks of a billion years younger could reveal how Mars became the world that he is.
The region is teeming with minerals, such as carbonates, which suggest that it once housed an underground aquifer – a potential refuge for organisms seeking to protect themselves from the harsh and erratic climate of their planet.
Emily Lakdawalla, geologist and editor-in-chief of the Planetary Society, asked a question that weighed on each site.
"What if the samples are not returned?
Golombek took the microphone. "We decided to set the standard for this conversation," he said. "It depends on whether you are optimistic or pessimistic, is not it?"
For the moment, he urged his colleagues, be optimistic.
Explore all sites
On the last morning of the workshop, there was no consensus on the best place to lay the rover. Some scientists said their opinions changed with each presentation, their ping-ponging opinions when they heard convincing evidence from supporters of each site. Others had become more rooted in their positions.
What if they did not have to choose?
The mission project's scientific team had designed an ambitious and extensive mission centered on a new landing site on the north-eastern edge of Syrtis, called "Midway", not far from the edge of the Jezero crater.
It would take hundreds of Martian days – the equivalent of several years on Earth – for the rover to move from one site to another, getting the best samples. The crossing would carry the rover on steep ridges, cluttered rocky fields and wind-swept terrain.
"It's a great exploration," said Ken Williford, the project's Deputy Chief Scientist.
Even by Mars standards, Midway was plagued by strangers.
The scientists had not been able to analyze in detail the rocks it contains, and the proposed 15-mile crossing is at the limit of what could be accomplished by a heavy rover.
There were many ways that it could end badly, some worried.
"But," retorted the project scientist, Ken Farley, "there is more than one way to fail.
"Personally," he continued, "I do not want to fail because we have not been ambitious enough to make the sample cache scientifically sound."
In the end, the decision would go to Thomas Zurbuchen.
As NASA's Associate Administrator for Science, he oversees more than 100 missions to understand the solar system and beyond.
"It's the most risky," he said about the $ 2 billion mission. "But suppose everything goes exactly as we hoped. The landing site for which I am the decisive leader will go down in history. "
A few days before the scheduled final briefing on the landing site options, Zurbuchen remained undecided.
He had attended a portion of the landing site workshop. There was still much to be considered: engineering safety assessments, the potential for follow-up missions, the need to balance astrobiology research with other scientific issues.
Then there was the vision that overwhelmed him when he closed his eyes to dream – a consideration that was neither financial nor scientific, but pure hope. A probe carrying samples of Mars rising rapidly to Earth. Scientists recover the cache and discover for the first time the debris of another planet. The laboratory where the rocks will be analyzed, the intricate instruments that will look for signs of old organisms.
A science class where his future grandchildren sit, reading a textbook with the name of the place he chose – a place where humanity has learned, for the first time, we have We have not always been alone.
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