Venus has long played second violin to her redder, smaller and more distant brother. Given how much we’ve learned that Venus is inhospitable, we’ve spent the majority of the past century pinning down some of our greatest hopes of finding signs of alien life on Mars.
Everything changed this week.
On Monday it was announced that a particular gas called phosphine had been spotted in the clouds above Venus. The gas is produced by microbes here on Earth, and after most of the known non-biological processes have been ruled out, the discovery has renewed hope for life on Venus. Now we have to be sure.
“To really get to the heart of this question, we have to get to Venus,” says Paul Byrne, a planetary scholar at North Carolina State University and self-proclaimed “Evangelical Venus.” In fact, it might be time to think that no fair on what the next mission to Venus should be, but what a whole new era of Venus exploration would look like: a fleet of multiple missions that explore Venus in concert as we currently do with Mars.
After all, there’s not much you can do with ground instruments. “Venus is extremely bright and many large ground-based telescopes cannot observe it properly,” says Sara Seager, an MIT astronomer and one of the co-authors of the new phosphine study. This brightness, caused by the intense reflection of sunlight from its thick clouds and evidenced by its proximity to Earth, essentially prevents our instruments from making detailed observations of the planet. It’s like trying to watch the road while the high beams of another car are pointed in your direction. Space telescopes might do better, but Seager says it’s still too early to say if they will suffer from the same problem.
And while telescopes on Earth can detect traces of phosphine and other interesting gases, there is no way to determine whether they are produced by life or by some other exotic chemistry, like volcanism. While Seager and his team have completely excluded known natural causes of phosphine on Venus, the planet may very well be home to a geochemistry we never thought possible. Answering these questions and setting aside natural explanations altogether means we need to get closer.
So let’s go to Venus!
Of course, that’s easier said than done. Surface temperatures reach 464 ° C and pressures are 89 times higher than on Earth. Only the Soviet Union managed to land on the Venusian surface – its Venera 13 lander operated for 127 minutes before succumbing to the elements in 1982. It is not easy to justify spending hundreds of millions or even billions of dollars for a mission that could end in 1982. a matter of hours and not giving us what we need.
An orbiter is therefore the best start. Unlike observations on the ground, orbiters can scan the atmosphere and would have a better time to observe how phosphine or other potential biosignatures change over time or in which regions they are most concentrated. Humans have experience with such missions. Venus’ last major orbiter was ESA’s Venus Express, which studied Venus for eight years until engineers lost contact with it, likely because it ran out of fuel. Currently, the only spacecraft exploring Venus is the Japanese orbiter Akatsuki, who arrived in 2015 to study the planet’s climate and weather. He does good science, but he has no instruments that could really probe atmospheric chemistry and look for signs of organic life.
An orbiter also offers the opportunity to achieve more daring projects and venture directly into the clouds. A sample return assignment could be possible, in which a spacecraft flies through the atmosphere and bottles gas to be brought back to Earth for laboratory analysis. Byrne notes that many proposals over the years have called for dropping something into the atmosphere itself to search for more biosignatures or even organic matter. To keep such a platform in the air as long as possible (potentially weeks or months at a time), engineers suggested slowing its descent using balloons or rotors.
Trying to find life on another planet, however, is not simply a walk from point A to point B. No mission to Venus will be able to do all of the work necessary to answer the question. NASA already has two potential Venus missions in the works. DAVINCI + is a probe that would dive directly into the atmosphere of Venus and study its chemical composition using multiple spectrometers during a 63-minute descent. VERITAS is an orbiter that would use a combination of radar and near infrared spectroscopy to look beyond the planet’s thick clouds and help us understand the geology and topography of the surface. Previous research suggests that the planet may have active volcanism and may have once hosted shallow oceans, but the inability to map the surface optically has made it impossible to verify these theories so far.
Each mission might reveal some interesting new clues that bring us closer to whether there is life there, but neither could answer that question on their own. Regarding phosphine, for example, DAVINCI + could have the chance to determine in which parts of the atmosphere this gas is concentrated. But if it is produced on the surface, the probe will not necessarily have the tools to identify the location. . VERITAS might find the site of an odd geochemistry, but without actually sampling phosphine directly in clouds, there wouldn’t be enough evidence to connect the two mysteries.
Byrne is optimistic that he wants to see a full exploration program for Venus similar to what we’ve already seen for Mars. On this planet, there are orbiters imagining the landscape, measuring atmospheric escapes and chemistry, and monitoring the weather. There are rovers tasked with understanding organic matter in the field and looking for signs of life. There are landers that examine the interior geology and measure the earthquake activity of the planet.
Imagine a similar program on Venus, with multiple missions performed at the same time. As part of such a program, VERITAS and DAVINCI + would work alongside other missions to isolate biosignatures like phosphine and really see if they are evidence of existence or not. “I wouldn’t like to have to choose one over the other,” Byrne says. “But even if we had both, I would always advocate more missions.”
These two missions (plus two more) are in the running to get the green light from NASA next April. The launch windows on Venus (when the planet is closest to Earth) occur every 19 months. If either were selected, it wouldn’t launch until 2026 at the earliest and would take at least a few months to make the trip.
Other missions could certainly take place – and sooner. India’s space agency is debating the launch in 2023 of a Venus orbiter called Shukrayaan-1 to study atmospheric chemistry. Rocket Lab, based in New Zealand, wants to launch a small satellite called Photon for a flight over Venus as early as 2023. This mission deploy a small probe in the Venusian atmosphere to collect data, although it would likely only carry a single instrument, limiting the scope of any resulting research. Byrne points out that it might be interesting to build a program out of several cheaper missions like Photon rather than a few very expensive missions like DAVINCI + and VERITAS. Seager says his immediate plans are to “conduct a mission concept study for a low cost agile mission,” in collaboration with Revolutionary initiatives (led by Russian billionaire Yuri Milner).
And while surface missions are difficult to accomplish, there has always been a constant stream of proposals for how to improve spacecraft engineering to make landers last longer. A project started by scientists at NASA, called Long-Lived In-situ Solar System Exploration, calls for the construction of electronic and hardware components capable of withstanding the harsh environment of Venus for 60 days. However, this type of lander would probably not be ready for the next decade.
Even though we don’t find any signs of life on Venus, it’s also interesting: it will mean that Venus and Earth were two planets that started out very similarly and ended up with radically different fates. “It still raises some deep questions that need to be answered,” Byrne says. “But to answer them, we need a program for studying the planet.”