Earth’s sister planet warns us that planetary climates can change dramatically
At a glance
Venus, the 2nd planet from our Sun, may have had oceans and been habitable to life before being transformed into an inhospitable wasteland.
By studying Venus, scientists learn how Earth-like planets change over time, and what conditions on Earth-sized planets orbiting other stars might be like.
You can help us build public support for the exploration of Venus by learning about proposed missions and sharing the passion, beauty, and joy of space.
Why study Venus?
The Sun rises in the east and sets in the west, except if you are on Venus. That’s because it rotates on its axis in the opposite direction from other planets, and nobody knows why. This is just one of the many mysteries of Venus, a cloud-shrouded hellscape with an atmosphere 50 times denser than Earth’s, and average surface temperatures of 470 degrees Celsius (878 degrees Fahrenheit)—hot enough to melt lead.
Venus is currently inhospitable, but it wasn’t always that way. Missions there have observed granite-like rocks on the surface, which require abundant water to form. In the early solar system when the Sun was cooler, scientists think the planet may have had liquid water on the surface for 2 billion years—far longer than Mars, which may have had liquid water for 300 million years. Water is the key to life as we know it, so did Venus once have life?
The hottest planet
Venus is the hottest planet in the solar system, even though Mercury is twice as close to the Sun and receives 4 times more solar energy. The reason? Mercury has no atmosphere, whereas Venus’ thick, carbon dioxide atmosphere creates a runaway greenhouse effect, trapping in heat.
How Venus transformed from a potentially habitable world to its current state is unknown. Its thick atmosphere traps in heat from the Sun, creating a runaway greenhouse effect that bakes the planet. By studying Venus, scientists learn how Earth-like planets evolve and what conditions exist on Earth-sized exoplanets. Venus also helps scientists model Earth’s climate, and serves as a cautionary tale on how dramatically a planet’s climate can change.
There is also a slim chance microbial life currently exists in Venus’s upper atmosphere, where mysterious dark patches absorb more than half the solar energy the planet receives. This region, approximately 50 kilometers above the surface, has Earth-like temperatures and pressures. Venus is on average almost 3 times closer to Earth than Mars, often shining as a bright evening star in our skies. Have we been looking for life on the wrong planet?
How we study Venus
Venus was the first planet to be visited by a spacecraft. In 1962, NASA’s Mariner 2 flew by the planet and discovered it was a hot world with no self-generated magnetic field. The Soviet Union became the world leader in early Venus exploration after that, sending multiple atmospheric probes and as many as ten landers to the planet. To this day, they remain the only nation to have landed spacecraft on the surface and transmitted both data and images back to Earth.
The Carl Connection
One of Planetary Society co-founder Carl Sagan's early scientific publications used radio observations to predict possible Venus surface temperatures.
Venera team/Don P. Mitchell
Images of Venus's surface from Venera 13
Composite views created from images of Venus’ surface taken by the Soviet Venera 13 Venus lander.
Due to thick clouds, it is impossible to see Venus’ surface without radar. NASA’s Magellan orbiter, launched in 1990, used radar to map Venus’ surface at the highest resolution to date. Magellan revealed that all of the planet’s impact craters are formed within the last 700 million years. This implies that Venus’ surface was completely reshaped by a worldwide volcanic event in its recent geologic past—but exactly what happened is still up for debate.
Magellan also found no sign of plate tectonics. On Earth, plate tectonics is a process in which sections of the planet’s outer crust glide over the mantle—the rocky inner layer above the core—allowing heat to escape through volcanism. Since we think Venus’s interior is similar to Earth's, the lack of plate tectonics means that volcanoes on Venus must work differently than on Earth.
Venus's surface from radar data
This 3D image of Venus’ surface was generated using radar data from NASA’s Magellan spacecraft. The 3-kilometer-tall volcano Gula Mons can be seen on the horizon, along with the 48-kilometer-wide Cunitz crater at near-center.
The European Space Agency launched the Venus Express orbiter in 2006. By observing hotspots on the surface and changing sulfur dioxide levels in the atmosphere over 6 years, the spacecraft collected the best evidence yet of active volcanism on Venus. Venus Express also discovered granite-like rocks across the planet that require abundant liquid water to form, solidifying the idea of the planet having past oceans.
Japan’s Akatsuki spacecraft is the only probe currently orbiting Venus. It studies Venus’s atmosphere in frequencies of light that human eyes cannot see, which helps scientists paint a better picture of what’s happening above the planet’s surface. These images can be processed to create beautiful enhanced-color pictures of the planet.
Active Venus Missions
Future Venus Missions
Venus' Lower Clouds
Akatsuki’s IR2 camera relies on heat emanating from the lower atmosphere of Venus to image the nightside lower clouds. The infrared radiation originating beneath the clouds silhouettes the lowermost cloud deck, so areas of thicker cloud appear darker in this photo. At lower left, the camera’s detector is overwhelmed by the brilliance of sunlight reflecting off the daylit crescent.
Only 3 missions have visited Venus in the past 30 years, and many scientists feel new missions are long overdue. A spacecraft with a higher-resolution radar could help us solve the mystery of how Venus’s surface changed within the last billion years. Landers and atmospheric probes would analyze the extent that water may have existed on the surface, what the planet’s atmosphere was like, and how it changed into its present-day state.
India aims to launch a Venus orbiter called Shukrayaan (English: “Venus craft”) in 2023 equipped with a radar and infrared camera to map the surface. The spacecraft has a total of 12 instruments, and India’s space agency ISRO has called for instrument proposals in which scientists from international space agencies, including NASA, are expected to participate.
DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus) consists of an orbiter and an atmospheric descent probe. The probe would make high precision measurements of trace gases in Venus’ atmosphere, helping firmly determine how much water Venus’ oceans had and how long they existed.
VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) would have a radar instrument with up to 100 times higher resolution than Magellan. This would give scientists a better handle on Venus’ geology and evolution and also reveal why the planet lacks large-scale plate tectonics.
What can you do to support Venus research?
The Planetary Society is following NASA’s decision whether to select a future Venus mission, as well as the scientific community's upcoming effort to prioritize exploration targets for the next decade. Sign up for our weekly email newsletter, The Downlink, to learn about new developments.
You can also learn more about the current Venus mission, Akatsuki: