Sue Smrekar really wants to return to Venus. In his office at NASA's Jet Propulsion Laboratory in Pasadena, California, the planetary scientist shows a 30-year image of the surface of Venus taken by the spacecraft Magellan, recalling how long it has been since the American mission circled the planet. The image shows a hellish landscape: a young surface with many volcanoes. There are more of them than any other body in the solar system, giant cracks, high mountain belts and temperatures hot enough to melt lead.
Venus's climate, currently superheated by greenhouse gases, may be similar to Earth's, with water in shallow oceans. It may even have subduction zones like those on Earth, areas where the layers of the planet sink under others.
“Venus looks like a bad case for Earth,” Smrekar said. “We believe they started with the same composition, the same water and carbon dioxide. But they took two completely different paths. So why? What are the main forces responsible for the differences?"
Smrekar is working with the Venus Research and Analysis Group (VEXAG), a coalition of scientists and engineers researching ways to revisit the planet after the Magellan mission decades ago. While their approaches differ, the group agrees that Venus could tell us something vital about our planet: what happened to the overheated climate of our planetary twin, and what does that mean for life on Earth?
Venus is not the closest planet to the Sun, but it is the hottest in our solar system. Between intense heat (480 degrees Celsius), acrid sulfur clouds and a crushing atmosphere 90 times denser than on Earth, landing a spacecraft there is incredibly difficult. Of the nine Soviet ships that reached the surface, none lasted longer than 127 minutes.
From the relative safety of space, an orbiter can use radar and near infrared spectroscopy to observe cloud layers, measure changes in the landscape over time, and determine if the surface is moving. He can look for indicators of past water as well as volcanic activity and other forces that may have shaped the planet.
Smrekar, who is working on an orbiting satellite project called VERITAS, does not believe Venus has plate tectonics like Earth does. But she sees possible hints of subduction - what happens when two plates converge and one slides under the other.
“We know very little about the composition of the surface of Venus,” she said. “We think that there are continents, like on Earth, that may have formed as a result of past subduction. But we have no information to really prove it."
The answers will not only deepen our understanding of why Venus and Earth are now so different; they could narrow down the conditions that scientists would need to find an Earth-like planet elsewhere.
Orbiters are not the only means of studying Venus from above. JPL engineers Attila Komjati and Siddhart Krishnamurti present an armada of hot air balloons that can control strong winds in the upper atmosphere of Venus, where temperatures are close to Earth's.
“There hasn't been a balloon mission on Venus yet, but balloons are a great way to explore Venus because the atmosphere is so dense and the surface is so harsh,” Krishnamurti said."A balloon is like a dream where you are close enough, but you are also in a much more supportive environment where your sensors can last long enough to give you really meaningful information."
The team will equip the balloons with seismometers sensitive enough to detect earthquakes on the planet below. On Earth, during an earthquake, vibration penetrates the atmosphere as infrasound waves (the opposite of ultrasound). Krishnamurti and Komyati demonstrated that this technique was feasible using silver balloons that measured faint signals over earthquake sites. And this is even without taking into account the dense atmosphere of Venus, where the experiment is likely to give even stronger results.
“If the surface of the earth moves, it will shake the air more on Venus than on Earth,” explains Krishnamurti.
However, to obtain this seismic data, the balloon mission will have to fight hurricane force winds on Venus. An ideal balloon, as determined by the Venus Research Group, would be able to control its movement in at least one direction. Krishnamurti and Komjati's team did not go that far, but they offered a middle ground: the balloons would move in the direction of the wind around the planet at a constant speed, sending their results back into orbit.
Among the many problems facing the Venus lander are clouds blocking the Sun: without sunlight, solar energy would be severely limited. But the planet is too hot for other energy sources to work here for a long time. "The solar system no longer has such surface environments."
By default, the mission lifespan will be shortened due to the spacecraft's electronics starting to fail after a few hours. Hall says the amount of energy required to run a refrigerator capable of protecting the spacecraft will require more batteries than the lander can hold.
"There is no hope of cooling the lander," he added. "All you can do is slow down the speed at which it collapses."
NASA is interested in developing "hot technologies" that can survive for days or even weeks under extreme conditions. While Hollus's Venus concept did not make it to the next stage of validation, it led to his current work on Venus: a heat-resistant drilling and sampling system that could take samples of Venusian soil for analysis. Hall is working with Honeybee Robotics to develop next-generation electric motors that power drills in extreme conditions, while JPL engineer Joe Melko is developing a pneumatic sampling system.
Together they work with prototypes in JPL's large steel-walled test chamber that simulates planetary conditions down to an atmosphere that is asphyxiant - 100% carbon dioxide. With each successful test, the teams bring humanity one step closer to pushing the boundaries of exploration on this most inhospitable planet.