Venus is Earth's evil twin – space agencies can no longer resist its attractiveness

The helicopter fell like a stone. He lost more than 1,500 meters above Maryland, twisting slightly as the ground approached rapidly. Although everything is going as planned, it did not calm James Garvin's nerves. He also did not realize that his seatbelt was not properly fastened – a moment that caused his heart rate to skyrocket.

Then, just 6 meters above the ground, the ride became even wilder as the pilots pulled the aircraft out of the waterfall and climbed to the sky, then fell back. The helicopter dropped ten times that day. And each time, Garvin pointed a camera at the ground through the open door to try to measure the topography of a rock quarry below, ranging from large rocks to smooth sand patches. Although his interests were barely terrestrial.

Garvin, a senior scientist at NASA's Goddard Space Flight Center in the Greenbelt of Maryland, is the principal investigator of a planned mission to Venus that would put a probe into its atmosphere. That's why he hired two pilots in August 2016 to plunge a helicopter to the ground while he tested what a Venus probe could photograph. The atrocious journey was worth it: the researchers would like to get their hands on images of Venus with as much detail as the landscape would become familiar. "These images would be as if you were landing in your garden," he says.

Garvin is not the only scientist to have prepared such a bold mission. Almost all space agencies around the world are developing a proposal to explore our long-neglected neighbor (see "The Decade of Venus"). The Indian Space Research Organization (ISRO) will be the first to take off when it launches a Venus Orbiter in 2023. The United States could follow closely. Garvin and his colleagues are among the rare groups that will soon be proposing missions to NASA which, if selected, will take off in 2025. The European Space Agency (ESA) is currently studying a proposal to send an orbiter to Venus in 2032. And the Russian space agency Roscosmos collaborates with the United States to send a bold mission on the planet from 2026 to 2033, which would include an orbiter, a lander who would return short-term readings and a research station that would survive much longer.

The interest regained contrasts with the fact that nations have long neglected Venus in favor of the pursuit of Mars, asteroids and other planets. Over the last 65 years, for example, NASA has sent 11 orbiters and 8 landers on Mars, but only 2 orbiters to Venus – and none since 1994. This has not lacked scientific interest. Since the mid-1990s, American scientists alone have submitted nearly 30 proposals from Venus to NASA. None has been approved.

But the momentum for exploring Venus is building, partly because scientists say it could be the secret to understanding what makes a planet habitable. Once the twin of the Earth, Venus is now a hellish home with surface temperatures of more than 400 ° C. Atmospheric pressures collapse with sufficient force to crush heavy machinery and clouds of sulfuric acid. blow in the sky. If researchers could understand why conditions on Venus have become so deadly, it would help them determine if life can exist on some of the thousands of rocky worlds discovered by astronomers in the galaxy.

While the scientific rationale for exploring Venus continues to grow, global scientists are devising new ways to study the planet and developing a laboratory technology that can survive the appalling conditions of its planet. area. And with India in the lead, there could soon be a parade of probes heading for the second rock of the Sun.

"It could be the beginning of a new decade of Venus," says Thomas Widemann, a global scientist at the Paris Observatory.

Double trouble

When humanity first reached the stars, she ventured to Venus. Our neighbor was the target of the first successful interplanetary survey (United States, 1962); the first planet on which a mission was crushed (Soviet Union, 1965); and the first foreign world to host a successful landing (Soviet Union, 1970). It was during this race in the space of Venus that scientists discovered a toxic and scorching world (see "Historical Missions"). This could explain why the interest in Venus has decreased. Scientists quickly understood that this planet would be neither a place of human exploration nor an outlet in search of life. It would be hard to study, even for short periods.

And yet, in many ways – size, density, chemical composition – Venus is twice the Earth. Recent research has even suggested that it could have looked like the Earth for three billion years, with vast oceans that could have been conducive to life. "That's what ignites my imagination," says Darby Dyar, scientist in planetary science at Mount Holyoke College in South Hadley, Massachusetts. "If that's the case, there was plenty of time for evolution to take place."

This could mean that Venus was (a bit surprising) the first habitable planet in the solar system – a place where life was as likely to happen as on Earth. That alone is a reason to return to the ancient ocean world. "Why are we investing so much time looking for life on Mars while she only had liquid water for 400 million years?" Asks Dyar. "And then there is Venus with three billion years of water and nobody likes it."

Still, there is no doubt that something went wrong. Although Earth and Venus started in the same way, the two countries followed radically different paths of evolution, perhaps diverging 715 million years ago. This may seem a reason not to visit the site, but scientists now claim that it makes the planet even more intriguing. If researchers could only understand what caused such a lethal metamorphosis in Venus, they could better understand what brought the Earth to become such a refuge for life.

"Venus plays a key role in understanding ourselves here: how life has evolved on our own planet," said Adriana Ocampo, chief scientist at NASA's headquarters in Washington DC.

It's a crucial question now that astronomers have discovered thousands of planets outside of our solar system – many of which are rocky worlds that gravitate around their stars at distances similar to those of Venus and the Earth at from the Sun. This means that many of these worlds might look like Venus. "The exoplanet community understands more and more that Venus is the best analog of the solar system for many of the rocky exoplanets we've discovered," says Laura Schaefer, an astronomer at Stanford University in California, who studies exoplanets. .

Off the radar

With such a tempting question left unanswered, it is easy to understand why the return of ISRO to Venus has generated so much enthusiasm. "I'm delighted that ISRO is doing that," said Dyar. "I am delighted that the international community is taking note of Venus and proposing missions. It's fantastic. "

Although ISRO's mission is shrouded in secrecy (Nature E-mail and called project scientists dozens of times, to no avail), it is clear that the agency is planning to send an orbiter drenched in instruments. When ISRO announced its mission at the end of last year, it published a list of a dozen instruments proposed by Indian scientists who have already been selected, which gives an overview of the mission. Two of these sensors will map the planet using radars, which is arguably the best method for scanning dense Venus clouds and tracing its surface from orbit.

That said, ISRO is a relatively young space agency with a limited number of successful landings on the Moon and Mars. And, like the programs of other nascent agencies, India's first Venus mission could be a proof of concept less science-based than engineering-oriented. But since even basic information about Venus is lacking, tiny steps will contribute to science.

One of these contributions could be new maps of the surface features of Venus – a major breakthrough in science. The last mission to map the topography of the planet was the NASA Magellan Orbiter, launched 30 years ago. Although these radar maps remain the foundation of Venusian geoscience today, they show topographic detail at a horizontal resolution of 10 to 20 kilometers per pixel on average (the image resolution can be two orders of magnitude greater) . With such limited topographic data, researchers have a blurred vision of the geology of Venus – but available maps suggest that plate tectonics could be put into action nowadays (see "Raising the Face of the Planet").

This is particularly tempting because many scientists believe that tectonic activity is an essential ingredient of life. Tectonic plates – those interlocking slabs of the earth's crust that fit together like puzzle pieces – move constantly, some slipping under each other and plunging into the interior of the planet in a process called subduction. For millions of years, this process has prevented the Earth from becoming too hot or too cold by recycling carbon dioxide trapped by heat between the atmosphere and the deep Earth. It acts as a natural thermostat, which could mean that restless planets are more likely to harbor life.

As such, scientists are eager to decipher the conditions for the onset of plate tectonics. That's why Suzanne Smrekar, a scientist in planetary science at NASA's Jet Propulsion Laboratory in Pasadena, Calif., Is staring at Venus – especially places that look suspiciously like places on Earth where subduction is taking place . Scientists agree that subduction is the first step on the path to plate tectonics. Yet, there are no clear signs of large moving plates on Venus – at least not on Magellan's decades-old maps. The San Andreas Fault, which forms the tectonic boundary between the Pacific land plate and the North American plate, for example, has a width ranging from a few meters to a kilometer – too narrow to appear in Magellan's topographic data.

But future maps could reveal such tectonic features. Smrekar is the lead investigator of a potential mission, known as VERITAS, which she and her team will soon propose to NASA. The geophysical mission would use a radar to map the topography of Venus with a higher resolution than previously, increasing the accuracy of about 15 kilometers to 250 meters and allowing scientists to discover features as small as the fault of San Andreas for the first time.

Although scientists do not know what they are going to find, they may find evidence of plate tectonics in the past. Such a discovery would explain why Venus has preserved an Earth-like environment for billions of years, says Smrekar – this natural thermostat would have kept the CO₂ in check. And that would explain how Venus became infernal. When plate tectonics ceased, CO₂ levels would have increased in the atmosphere and trapped a quantity of heat such that the oceans vaporized.

But this is only one possible conclusion. Some scientists want to study the atmosphere of the planet, which contains another set of equally tempting secrets.

The probe proposed by Garvin, called DAVINCI, would go into the atmosphere to measure the infusion of toxic compounds. The isotopes of rare gases, especially xenon, could give scientists a window into the volcanic history of the planet and indicate if Venus had started with as much water as the Earth. "The atmosphere of Venus is this hidden laboratory that tells us its story," says Garvin. "And in fact, most measurements in the atmosphere are terribly incomplete." In addition, the probe would take images of the surface – thanks to Garvin's terrifying helicopter flights – to the last few seconds before it hits. .

VERITAS and DAVINCI will participate in the NASA competition on July 1st for their future Discovery missions: a range of inexpensive planetary probes at a cost of $ 500 million each. And the rumor says they are not alone. There could be up to five Venus missions (including a balloon) among dozens of proposals to study various objects in space. The latest NASA Discovery Contest, for example, in 2015, examined 27 proposals – ranging from probes exploring asteroids, moons and planets in the solar system to telescopes that would mimic its surroundings – before choosing two missions to fly.

At the end of this year, the administration will select some missions to study and will choose the final project in two years. Smrekar and Garvin hope each of their missions will be selected, in part because they have proposed similar missions in the latest Discovery competition. Both were chosen for further study, as well as three others. If one of Venus' missions succeeds, it will be launched in the mid-2020s.

Even after this period, Venus could remain a hub of interplanetary activity. ESA recently chose a Venus spacecraft called EnVision, along with two other finalists, as a mission that can fly as early as 2032. Like Veritas, EnVision is an orbiter. But unlike VERITAS, which would map the entire planet at a resolution of 15 to 30 meters, EnVision will analyze small parts of the planet with a resolution of up to 1 meter. At this level of precision, scientists might be able to see the undercarriages left behind by the Soviet Union.

They could even choose the type of rock on which the undercarriages lie. This is possible because astronomers in the early 1990s discovered that certain wavelengths of light could cross the CO₂ mist that hides the Venusian surface. An orbiter equipped with a spectrometer set on these "windows" transparent in the spectrum of light could analyze the composition of the planet's surface above the clouds. It's an exciting prospect, especially if scientists can spot granite.

Like basalt, granite is formed when molten magma cools and hardens. But unlike basalt, the granite recipe usually requires large amounts of water – which occurs on Earth when the ocean-rich ocean crust sub-condenses under another plate. So if Venus is rich in granite, it will probably overflow once with liquid water.

And that could be the best clue that the planet was once a pale blue dot very similar to Earth today – another clue in their divergent histories (see "The Mystery of Water").

The problem is that there are only five narrow spectral windows in the atmosphere of Venus that are truly transparent. With so little information, scientists did not know if they could tell the difference between granite and basalt. Jörn Helbert, a scientist in planetary sciences at the Planetary Research Institute of Berlin, therefore subjected both types of rock to conditions similar to those of Venus and reproduced them in these narrow frequency bands. His experience suggested that the two rock spectra were radically different and that future missions could use the windows. He and his colleagues built an instrument to use this trick to map any granite on the Venusian surface. It would fly on both VERITAS and EnVision.

At your fingertips

To fully understand the surface, a number of scientists really want to put a gear on our toxic twin – a feat that has not been accomplished in 35 years. Although the Soviet Union sent several landing gear to Venus, those who survived quickly succumbed to the harsh environment of the planet: the most durable has persisted for only 127 minutes.

But scientists hope to break this record and have already designed a technology that can last not minutes, but several months. A team at NASA's Glenn Research Center in Cleveland, Ohio, is building a station that is expected to survive for at least 60 days. Instead of using its mass to absorb the heat or to fight against the conditions related to refrigeration, the LG would use a simple silicon carbide electronics (hybrid silicon and carbon commonly used in sandpaper and fake diamonds) that can withstand the Venusian environment. "It's the real game changer for Venus exploration," says Philip Neudeck, Electronics Engineer at the Glenn Research Center.

The team has already tested the circuits in a Venus simulation chamber, a 14-tonne stainless steel tank that mimics the temperature, pressure and specific chemistry of the Venusian surface. The researchers used these results to design a fixed surface probe called LLISSE (Long-Term In-Situ Solar System Explorer), which should be ready to fly in mid-2020 and be offered to other countries. "Any Venus mission is welcome to use LLISSE," says Gary Hunter, Electronics Engineer, also at the Glenn Research Center. He and his team took care of designing a toe-sized undercarriage, small and light enough for him to take part in many future missions.

Despite its small size, LLISSE would be able to record temperature, pressure, wind speed, wind direction, amount of solar energy at the surface and some specific chemicals in the lower atmosphere. And he would do it for months, making a crucial contribution to models of the Venusian atmosphere. "Imagine if we were trying to say that we knew the weather on Earth by going outside for 127 minutes," Hunter says. This is the current record for all weather data on Venus.

Scientists in Roscosmos already want to use this new technology. In a joint proposal with NASA, they are working on a mission called Venera-Dolgozhivuschaya (where the latter means long), or Venera-D for short. Such a mission would include a menagerie of elements: an orbiter, a lander and a living station. The lander would include a number of advanced instruments but would only last a few hours; the long life station would have a simpler design but would continue to take measurements for months. The station will probably be NASA's LLISSE.

At least that's basic architecture – but the mission could include even more. This year, the Venera-D team released a report covering a number of potential additions, including a balloon that can explore the cloudy atmosphere. And this opens the possibility of looking for life on Venus. All other missions proposed to date are to determine if Venus was livable before. But a balloon might be able to search for life in the only environment where it could survive today: the sky.

"You can imagine that there is somewhere between the hostile and hostile surface and the cold emptiness of outer space, where there are conditions – like Goldilocks", which are quite conducive to life ", said Dyar.This layer would not only have a pleasant temperature, but could also contain nutrients, liquid water and energy from the sun.If life had ever existed on the planet, it could have be carried into the clouds and survive after the surface has become toxic.

But even without a balloon, the three main components of the Venera-D mission would provide excellent science, says Ocampo. "It would be a decisive mission in the understanding of Venusian science," she says. "We had never had a mission similar to this one."

Unfortunately, Venera-D has not yet been selected and many scientists have expressed concern that the subject has been discussed for a long time and that it still does not have the proper funding. But Ludmila Zasova, a senior scientist at the Moscow Space Research Institute's Venera-D mission, hopes this will change this year.

This is not the only big ambitious mission in preparation. Some US teams plan to submit Venus projects to NASA's New Frontiers program, capped at $ 1 billion, and the Flagship mission program, which costs even more. Because Venus' proposals have performed well in previous competitions (often just behind the selected proposals), scientists believe that there is a good chance they will now reach the top.

With each space agency looking at our neighbor, Venus should receive a fleet of visitors over the next few decades. And while they all plan to address the issue of livability in one way or another, Garvin is convinced that whatever they find, it will be "beyond beyond our wildest dreams. Perhaps they will prove that Venus was once an oceanic world. Or maybe they'll find out he's tectonically active today. "We need to know," he says. "Because she's waiting to tell us something and I do not want to miss the boat."