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Mars or Venus: Which is More Suitable for Human Life?

Updated: Mar 31, 2021

On July 30, 2020, NASA's rover, Perseverance, launched from Cape Canaveral Air Force Station into space. Predicted to land on Mars in February of 2021, its purpose is to investigate Mars and detect evidence of microbial life from the past. Mars, what scientists speculate was once a warm and wet planet is believed by many to be the most capable planet to host human life in our solar system. While Mars may be the public's and scientists' primary focus, is Venus another suitable option? First, we must look at the two planets’ properties, focusing more on Venus due to a common lack of knowledge about its properties. Next, we must consider if these properties make it ideal for humans and our necessities.

Their Properties – The Atmosphere/Weather

When we look at Venus' atmosphere, we automatically assume that it cannot support human life. Believed to have once been covered in water and have possessed an atmosphere similar to Earth, Venus is now a carbon dioxide-filled planet that rains sulfuric acid, averages a temperature of 467ºC, and a pressure of over 1,300 pounds per square inch (Sitrone et al.). The large quantity of CO₂ created mostly from volcanoes builds up and results in the greenhouse effect (Green). This occurrence is where the carbon dioxide traps the sun's heat, which makes the atmosphere warmer. But, although the surface is currently inhospitable due to the greenhouse effect, "a cloud layer just 31 miles below the top of its atmosphere… has a pressure similar to that at ground level on Earth" (Sitrone et al.). While walking on the surface of Venus would be like swimming 3,000 feet underwater, traveling 31 miles above the surface would be at 1,000 hectopascals (hPa) compared to Earth's 1,013 (Davis). Temperatures would also be quite similar to Earth's, ranging from 0ºC to 50ºC. Also, "the atmosphere above this altitude is also dense enough to protect astronauts from ionizing radiation from space" (Dorrian). Dense enough, yet still close enough to the sun, solar radiation can generate up to 1.4 times more power on Venus than Earth (Daley). This could help power blimps such as those displayed in HAVOC, the High Altitude Venus Operational Concept. HAVOC is a plan fabricated by NASA that would send a crew to Venus for 30 days, and they would live in a vehicle similar to a blimp. As stated previously, the similar pressure and gravity compared to Earth would allow blimps to function nearly identical to those on Earth. Also, solar panels covering the surface would power the blimps. Although this mission is unlikely to occur due to NASA's extensive focus on Mars and lack of statistics on Venus, the idea of avoiding Venus' surface and living in the atmosphere is very much possible. Addressing the sulfuric acid present, a resistant layer of poly tetra fluorine could coat the surfaces of anything exposed to the atmosphere. Additionally, electrolysis could extract sulfur from the acid– made of hydrogen, oxygen, and sulfur– leaving behind drinkable water (Weigel).

Image Created by Joey Serricchio

So, while numerous conditions appear to be inhabitable, various solutions could be implemented to address them. Lastly, a bonus of settling above the surface would be maneuverability. Whether for research purposes or hazard avoidance, "a hovering settlement would not only have the ability to explore the 'X' and 'Y' axes of its surroundings but would also maintain the option to change its altitude in the 'Z' direction" (Weigel). As time goes on and there will be more urgency to find a second home, technology will advance, and humans will become more knowledgeable about what is needed to live on comfortably, or above, Venus.

Like Venus, Mars' surface once contained an abundant water supply but now includes a minimal supply (Sharp). But, scientists believe that water, a basic necessity, is "trapped under Mars's surface, perhaps a remnant of when the planet once had seas and lakes billions of years ago" (O'Callaghan). Additionally, Mars' lack of oxygen – around only 0.23% – is believed to result from its low gravity and magnetic field. The MAVEN – Mars Atmosphere and Volatile Evolution – mission examines the belief that "over millions of years, the sun's pressure stripped the lighter molecules from the atmosphere, thinning it out" (Sharp). The thin atmosphere contributes to a small amount of oxygen and an icy surface, ranging anywhere from -125ºC to 20ºC. But, similar to how technology can make Venus more habitable, scientists hope to do the same with Mars. Addressing how humans would breathe in an atmosphere with 96% CO₂, MOXIE – Mars Oxygen ISRU Experiment – would separate the oxygen atom from a CO₂ compound, combining two oxygen atoms resulting in O₂ and CO. This is an example equation of what MOXIE does: 2CO₂ → O₂ + 2CO. Despite many unideal conditions on Mars, scientists' belief that there is water ice beneath the surface is encouraging when considering if life previously existed on Mars, currently exists on Mars, and if Mars will be able to host humans in the future. Ashwin Vasavada, a project scientist for the Mars Scientist Laboratory, says that Mars is “a place that you can go today that's like going to early Earth. You remove that dusty exterior of Mars, and you have this planet that is just so reminiscent of Earth." A large concern with Mars, though, is its lack of gravity compared to Earth or Venus.

Image Created by Joey Serricchio

The Impact on Humans – The Problem with Reduced Gravity

While Mars' gravity is only 38% strong as Earth's, Venus' is 90% strong. To understand the significance of Mars' gravity, we must consider what would happen to our bodies. The muscles and bones that surround and support our spinal column – the calves, quadriceps, buttocks – are what allow us to walk and stand up (Fong). These parts are always fighting gravity, keeping them strong and able to hold our human form. On Mars, our muscles would have to work a lot less, which would weaken and deteriorate our muscles – this is known as atrophy. For example, experiments exploring the importance of gravity observed that ⅓ of rats' muscle bulk was lost after nine days in space (Fong). A lack of gravity would not just affect our muscles; it would create a ripple of adverse effects that would compromise our health and capabilities. The combination of lesser gravity – which increases the size of cells – and immobility – which lessens the production of red blood cells – will likely lead to decreased strength, cognitive function, and ability to fight infection (Gaskill). To understand what it would take even slightly to mitigate the effects of Mars' gravity, astronauts on the International Space Station, where the gravitational force is 90% of Earth's, must exercise two and a half hours a day. Such an intense physical regimen to combat the effects of gravity is likely something that every human would have to do if living on Mars ("What happens to muscles in space?"). Even exercise would not be enough, though – we would have to develop another way to either increase gravity's force or create life support systems (Fong). Scientists are still figuring out how to host four humans on Mars, let alone the entire human race. So, while Venus' gravity is not identical to Earth's, it is far more sustainable for human bodies than Mars and would require less problem solving due to its lesser impact.

So, which is better?

At this time, there is not enough evidence to give a definite answer. While Mars' weather and atmosphere are more survivable, Venus' gravitational force and conditions above the surface are more suitable for the human body. A large reason why Mars gets more attention, astrophysicist Gabe Perez-Giz says, is "the fact that we cannot live on the Venusian surface." Regardless of which planet is better, we could use evidence from both worlds to make independent discoveries and advance our knowledge of the two. Richard McGuire Davis Jr., Assistant Director for Science and Exploration at NASA, says that "Terraforming has a connotation of humans making another planetary body, like Mars, Earth-like. But really, it's about humans changing their environment to make it more supportive of our need." When considering other planets to live on, whether it be Mars or Venus or another, we must accept that we currently know of no planet as suitable as Earth. Therefore, we must make compromises and colonize the planet that is ideal for humans.


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