Seeing it as the most habitable planet after earth, there are a total of eleven robotic missions exploring Mars. But with all the focus dedicated to humans living on Mars, we tend to overlook Earth's other neighbor, Venus
Seeing it as the most habitable planet after earth, there are a total of eleven robotic missions exploring Mars, a combination of orbiters, landers, and rovers.
But with all the focus dedicated to humans living on Mars, we tend to overlook Earth's other neighbor, Venus which has a lot going for it that might make it a better candidate for long-term human habitation.
But first, why is Mars such a crowd-pleaser?
Life on Mars
The average temperature on Mars is -62.7 °C (Earth 14 °C). The temperature on the surface of Mars is also subject to a greater level of variation, ranging from 20 °C during the summer in the equatorial region at midday to −153 °C during winter at the poles.
The air is a toxic fume composed overwhelmingly of carbon dioxide (96%). Then there's the matter of radiation which is over four times as much as on earth. Looks hopeless but there are solutions.
Extremes in temperature and high radiation levels can be mitigated by creating structures on the surface that can maintain an atmosphere and provide sufficient radiation shielding.
Food, water, and energy could also be harvested locally using local soil to grow food, local ice to provide drinking and irrigation water, and solar panels and wind farms to generate electricity.
It's also suggested that Mars could be ecologically transformed to accommodate Earth life forms (a process called terraforming).
Three general steps are involved: thickening the atmosphere, warming it up, and melting the polar ice which can be accomplished by doing one thing: triggering a greenhouse effect.
One way to do this would be to import volatile compounds like ammonia and methane, both of which are in abundance in the outer Solar System.
Another idea is to cover the Martian surface with low albedo (dark) material or plants, which would cause more heat to be absorbed on the surface.
Some more radical ideas include using an orbital mirror to direct sunlight onto the ice caps largely composed of dry ice (frozen carbon dioxide). The release of sublimated CO2 and water vapor would have a profound greenhouse effect.
Once all that is done, the process of converting the atmosphere to something breathable will commence. By introducing photosynthetic organisms, like cyanobacteria and lichens, to convert CO² into oxygen gas, humans can start to breathe on Mars.
The Case for Venus
Just 700 million years ago, Venus was a warm and wet planet where oceans covered 80% of the surface. Today, it’s a hellish place mostly due to a severe greenhouse effect, which if reversed, humanity would have a planet closer to Earth that is roughly equal in size, mass, and gravity.
Venus is the closest planet to Earth, ranging from a minimum distance of about 38.2 million km to a maximum of around 261 million km. In contrast, the average distance between Earth and Mars is about 225 million km, ranging from 55.7 million km to around 401.3 million km. Venus' gravity is the equivalent of 90% to what we experience here on Earth whereas Mars is roughly 38% of Earth's.
But Venus is the hottest planet in the Solar System, with an average surface temperature of 464 °C. The atmosphere is also a toxic fume, composed overwhelmingly of carbon dioxide. A single "solar day" on Venus lasts 116.75 days or close to four months for the Sun to set and rise again compared to 24 hours here on Earth. Venus is also isothermal, which means that it experiences virtually no variation in temperature and so it doesn't experience seasons or anything we might consider a day-night cycle.
Luckily, Venus could be terraformed into an ocean planet with mild temperatures and endless beachfront property. As with Mars, it comes down to three major goals. They include:
Seeding the atmosphere of Venus with genetically engineered cyanobacteria could gradually convert the atmospheric carbon dioxide to organic molecules. Also flooding Venus' atmosphere with hydrogen would trigger a chemical reaction, creating graphite and water which would fall as rain and cover 80% of the surface in oceans.
Another proposal is to use solar shades using a series of small reflective spacecraft in Venus' atmosphere to divert sunlight, thereby reducing global temperatures.
In 2003, NASA scientist Geoffrey A. Landis released a study titled "Colonization of Venus," where he indicated how cities could be built above Venus’ upper cloud layer. At this altitude, temperatures would be tolerable for human beings, and the atmospheric density would allow the cities to remain afloat providing initial living space for colonists.
With Venus covered predominantly by oceans, the surface would essentially be a giant archipelago with a few larger continents. Think of the Caribbean, Polynesia, and the Greek Isles, but on a planet-wide level!
Living organisms on Venus?
In late 2020, scientists studying the atmosphere of Venus announced the surprising – and controversial – discovery of phosphine, a chemical that, on Earth, is produced primarily by living organisms. In March 2021, a study from Rakesh Mogul suggested other “biologically relevant chemicals” in Venus’ atmosphere that appear to be in a state of disequilibrium: another hallmark of life. The peer-reviewed results were published in Geophysical Research Letters on March 10, 2021.
New missions to Venus
Missions led by the European Union and Japan have revealed that Venus has much more complex atmospheric chemistry than previously thought. These new revelations have led space agencies to plan their next missions to Venus. The Indian Space Research Organization (ISRO) is planning an orbiter launch in 2024, and Russia's Roscosmos is aiming for a lander mission in 2029.
ISRO's planned mission will use radar and infrared spectrometry to gather data over a four-year period. NASA's two proposed missions would study Venus's atmospheric chemistry and geochemistry, respectively. Experts advocating for renewed Venus missions say that the efforts will help scientists better understand planets in our own solar system and beyond, and could provide insights into the prevalence of life in the universe.
NASA, the European Space Agency, China, and a private company are also mulling plans for their own trips.