Venus, often referred to as Earth’s “sister planet” due to its similar size and mass, presents a starkly different environment. It is shrouded in a thick, toxic atmosphere that creates extreme conditions. Venus does not possess free, breathable oxygen in any significant quantity.
Venus’s Dense Atmosphere
The atmosphere of Venus is exceptionally dense and hot. It is primarily composed of carbon dioxide (CO2), making up about 96.5% of the atmospheric gases. Nitrogen accounts for most of the remaining 3.5%, with only trace amounts of other gases present. This contrasts sharply with Earth’s atmosphere, which is about 78% nitrogen and 21% oxygen.
On Venus, the atmospheric pressure at the surface is about 92 times that of Earth’s, equivalent to the pressure experienced 900 meters (3,000 feet) underwater on Earth. Surface temperatures average around 462 degrees Celsius (863 degrees Fahrenheit), hot enough to melt lead. While oxygen atoms exist within compounds like carbon dioxide or sulfur dioxide, and atomic oxygen (O) has been detected in the upper atmosphere, molecular oxygen (O2)—the form we breathe—is not abundant. This atomic oxygen is a highly reactive, non-breathable form, created when solar ultraviolet radiation breaks down CO2 and carbon monoxide.
The Runaway Greenhouse Effect
Venus’s extreme atmospheric conditions are largely a result of the runaway greenhouse effect. Venus boasts the hottest surface temperatures of any planet in our solar system, despite being further from the Sun than Mercury. This is due to its thick carbon dioxide atmosphere, which efficiently traps heat from the Sun.
Scientists propose that early Venus may have had liquid water oceans, similar to Earth. Its closer proximity to the Sun led to higher temperatures, causing this water to evaporate into the atmosphere. Water vapor, a potent greenhouse gas, further intensified the warming, leading to a feedback loop where more evaporation caused more warming. As temperatures soared, water molecules in the upper atmosphere were broken apart by ultraviolet radiation, with hydrogen escaping into space and oxygen reacting with other elements. This process prevented the carbon cycle, which on Earth helps regulate CO2 and produce oxygen, from ever establishing itself on Venus.
Implications for Life
Venus’s surface conditions make it an environment where life as we know it cannot survive. The thick clouds also contain corrosive sulfuric acid droplets.
Despite the inhospitable surface, some theoretical discussions have explored the possibility of microbial life existing in the planet’s upper atmosphere. At altitudes between 48 and 60 kilometers (30 to 37 miles), temperatures and pressures are more Earth-like. However, even in these layers, the presence of highly acidic sulfuric acid clouds presents a significant challenge for known life forms. While some research has investigated whether certain molecules could indicate biological processes in these clouds, this remains speculative and requires further investigation.
Future Exploration and Research
Understanding Venus’s past and present is important for comprehending planetary evolution. Several missions are planned or underway to explore Venus. NASA has selected two new missions, DAVINCI+ and VERITAS, expected to launch between 2028 and 2031. DAVINCI+ will investigate the atmospheric composition to understand its formation and evolution, while VERITAS will map the surface to study its geological history and why it diverged so much from Earth.
The European Space Agency (ESA) is also developing EnVision, an orbiter planned for launch in the early 2030s. EnVision will study Venus from its inner core to its upper atmosphere, to determine the interplay between its geological activity and atmosphere. These upcoming missions will provide data to further understand Venus and the evolution of rocky planets.