In Edgar Rice Burroughs science-fantasy novel Pirates of Venus, the hero crash lands on Venus (Amtor) when his rocket ship is thrown off course. He discovers a verdant world of giant vegetation and unmapped oceans, wreathed in thick clouds and – of course – populated by monsters and princesses in peril.
In reality, Venus is anything but hospitable to life. Our closest neighbour is a hellworld: hot enough to melt lead, with crushing pressures and toxic clouds. The search for life has largely focused on Mars with its low gravity, clear skies and tantalising prospect of alien bacteria.
Yet one or two billion years ago, Venus might have looked a lot more like Burroughs’ Amtor.
Amtor it was wet once
Computer simulations published last month suggest early Venus might have enjoyed moderate temperatures and even light snowfall. There could have been shallow oceans and, with them, the possibility of life.
“There’s a lot of ‘mights'”, writes Michael Way at the NASA Goddard Institute for Space Studies. “But that’s because we don’t know how life got started on Earth!” If life started in our planet’s oceans – a question that remains open – the same might have been true on a watery Venus.
The search for life
So could Venus have evidence of ancient life? “To detect extinct life, we’d first need to figure out which parts of the modern Venus surface might be ancient enough to date back to the time when Venus had water. We’ll have to learn more about the surface geology first to do that,” writes scientist and sci-fi author Geoffrey Landis from the NASA John Glenn Research Centre.
One problem is much of Venus is covered with smooth lava plains, probably from volcanic eruptions around 750 million years ago – around the time Way’s team think the planet stopped being habitable. These would have wiped out any evidence of life. “Finding life on Venus is a much tougher prospect compared to Mars,” says Way. “The area of Venus that remains unresurfaced is much smaller than the entirety of Mars.”
The best place to look might be highland areas, called tesserae and similar to Earth’s continents. “They are apparently the oldest terrains on Venus – so they’re a good place to understand the past,” writes Colin Wilson, a researcher on Venus’ atmosphere at Oxford University.
Our maps of Venus come from the Magellan orbiter, which used radar to penetrate the thick clouds. Proposed future orbiters, such as the European Space Agency’s EnVision or the NASA VERITAS mission, could provide more detailed images. “This could help us examine these tesserae regions and, more generally, to try to figure out the geological history,” writes Wilson.
Rovin’… rovin’… rovin’
Future landing craft could analyse rocks to look for fossilised bacteria or other signs of ancient life. But designing a lander to survive Venus is tougher than it looks. Pressures at the surface are equivalent to diving a kilometre (~3,000 feet) beneath Earth’s oceans, and temperatures far hotter than a kitchen oven.
The harsh conditions mean Venusian landers historically had a short life expectancy. The Soviet Venera probes – launched in the 1980s – lasted a maximum two hours before ceasing transmissions.
How easy would it be to collect rock samples? “With present-day technology, I would say extremely difficult,” writes Way. A future lander would probably work similarly to Martian missions, and would collect nearby rocks for analysis with a mass spectrometer.
The problem is managing the process of bringing hot rocks inside the lander. “The spacecraft is already using tremendous energy to keep its electronics from melting,” writes Way. Under such harsh conditions, “it would be difficult for the spacecraft to maintain its desired operating temperature and pressure.”
One solution might be breaking the rocks into very small pieces. But, “having a sophisticated enough robot arm,” writes Way, “is again a technology that has not been developed.”
All that said, some information about Venus geology should be obtainable with today’s technology. Soviet landers of the 1970s and 80s collected soil samples and NASA has funded the development of high-temperature drills.
Sailing the surface
There are proposals afoot to develop technology capable of withstanding the harsh conditions on Venus. The Venus Landsailing Rover, or Zephyr, is a new type of lander proposed by Geoffrey Landis.
“The original plan for Zephyr was to do a mission similar to the Mars Exploration Rovers, to look at the geology and mineralogy of rocks on Venus to learn more about the surface,” writes Landis.
Zephyr is designed to work at low power to avoid overheating. Instead of a powered engine to drive it along, the craft is carried by the light winds of Venus. It has a sail with two moving parts. One to set the sail and the other to set the steering position. The rover also uses sensors that work inside jet engines. These can function even at surface temperatures of 450 degrees Celsius (840 degrees Fahrenheit).
Zephyr is a design study, not a mission, and doesn’t have a launch date. “A possible plan would be to fly a technology demonstration to Venus to show that the electronics work around 2020 or so, and then fly the Zephyr mission a few years after that,” writes Landis.
Future missions to Venus might look specifically for ancient life. “Note though that the surface might not be the best place to look,” says Wilson. The high temperatures not only make it difficult to explore, but also limit the preservation of biological materials.
The most “habitable” environment for life on Venus today is 50 – 60 km above the surface, amid the clouds, where temperatures are cooler and liquid water could exist. Although not a great place for life today as there are few nutrients (“although it has been suggested!” writes Wilson), the atmospheric chemistry could give clues to whether life flourished in the past.
Planes or balloons could explore the Venusian atmosphere. “And this is totally achievable today,” Wilson writes. He’s submitted a balloon mission proposal, called European Venus Explorer (EVE), to look at cloud chemistry and possibly to detect particles. There’s also been an American balloon proposal, called VALOR.
Both proposals follow in the footsteps of successful Soviet missions. The helium balloons launched by the Vega 1 and Vega 2 spacecraft floated in the clouds for 46 hours before their batteries ran out. “If the Soviet Union could achieve this in 1984, we have confidence it’s achievable with today’s technology,” Wilson writes.
An inflatable wing
The most exciting idea for exploring Venus’ atmosphere is probably the Venus Atmospheric Manoeuvrable Platform (VAMP), being developed by Northrop Grumman. “We’re excited by this mission because it could carry ten times more scientific payload [equipment] than a conventional balloon,” Wilson writes.
The VAMP is an inflatable flying wing powered by solar cells. During the day, this revolutionary plane would be powered by solar energy. During the night, it would float near the base of the cloud layer and wait until the winds brought it around to the dayside of the planet.
Earlier this year, however, the VAMP was still fairly early in development. “More development work, including demonstration flights on Earth, would be needed before this can be a credible proposal to NASA,” Wilson writes.
The cloud cities of Venus
Humankind could take our first steps on Mars by the 2030s, but some scientists believe a crewed mission to Venus’ atmosphere would be easier than exploring the red planet. NASA’s High Altitude Venus Operational Concept (HAVOC), for example, has crew staying up to a year in an airship drifting 50km above the planet’s surface.
The ultimate aim could be floating cities, with a permanent human colony, in the clouds high above Venus’ baking surface.
“The cloud-level atmosphere of Venus is among the most benign in the solar system,” writes Wilson. “The crew of a cloud-level balloon mission could walk around outside – on a catwalk, or in the basket of their balloon – without wearing a pressure suit or temperature-controlled clothing.”
He explains that they’d need an oxygen mask, as there’s no oxygen and the carbon dioxide atmosphere is poisonous. A jumpsuit might also be advisable for long trips outside, to protect the wearer from the thin sulphuric acid clouds, but scientists could make short trips with bare skin provided they showered afterwards. “It’s a far cry from the enormous pressure suits you’d require in space or even at the surface of Mars,” he writes.
So could a manned mission find life on Venus? Wilson is skeptical. “I don’t see how sendings humans would help,” he writes. Before launching a manned mission to the atmosphere, you’d need to launch lots of robotic missions – even if just to test the technology. “And we would learn a lot from those missions.”
Science apart, a human colony on Venus has a romantic allure. Perhaps one day, in the far future, our descendants will send a lander to the hell world below their home… And finally find evidence of life.
UPDATE 16.09.2016 Slight edits after fact-checking with my interviewees.
Note: The EuroVenus consortium, a collaboration to study Venus of dozens of scientists from across Europe, recently released a 52-minute documentary highlighting some of their work. Hat tip: Colin Wilson.