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Life on Mars vs. Life on Venus

Updated: Mar 31, 2021

Could you imagine living on a different planet? Researchers have been exploring the possibility for decades, and there might just be a chance that you find yourself waking up on Mars or Venus in the future!

Background on Venus

Venus is the second planet from the Sun and is the closest planet to Earth. Venus is the hottest planet in the solar system, with surface temperatures exceeding 880 degrees Fahrenheit (471 degrees Celsius). Venus has a radius of 3,760 miles, which makes it slightly smaller than Earth. Venus is covered in craters, mountains, valleys, and volcanoes. Venus is also covered with clouds that scatter sunlight, causing the planet to appear white from space. At this point, no human has been to Venus, and the spacecraft that are sent there do not last long because the high surface temperature of Venus overheats them. Venus rotates "backward" (from east to west), and it completes one rotation every 243 days, which is the longest rotation of any planet in the solar system. Venus does not have any rings or moons, and its slow rotation causes its magnetic field to be weaker than Earth's. An essential aspect of Venus's atmosphere is that it is an anaerobic environment, which means that it lacks free oxygen and is instead composed of carbon dioxide and sulfuric acid clouds.

Background on Mars

Known as the "Red Planet," Mars was named after the Roman god of war. Due to its red appearance, Mars is often associated with blood, warfare, and death. Mars has two moons: Phobos (Greek for "fear") and Deimos (Greek for "terror). Mars is the fourth planet from the Sun and the seventh-largest planet in the solar system, with 2,106 miles. Mars's atmosphere consists primarily of carbon dioxide, nitrogen, and argon. Mars is farther from the Sun than Earth is, so Mars's year is about double the length of Earth's (687 days), with each season lasting around 199 Earth days. Mars's atmosphere is thinner than Earth's, lowering the amount of heat that can be trapped at the planet's surface, leading to an average surface temperature of -81 degrees Fahrenheit, 138 degrees colder than the average temperature of Earth. Following Earth, Mars is the second most explored planet by humans. Scientists have concluded that Mars is similar to Earth with clouds and wind, a 24.6 hour day, seasons, volcanoes, canyons, and more.

Phosphine on Venus?

In a study published in September, a team of researchers claimed that they found amounts of phosphine in the clouds of Venus at quantities that were thousands of times greater than those found in Earth's atmosphere. Our current knowledge of phosphine suggests that it can only be produced by life on planets such as Earth or Venus. As a result of this, scientists have determined that phosphine is a biosignature, which means it is an indicator of life. Phosphine is naturally produced on Earth by bacteria that live in anaerobic environments, including landfills, marshlands, and animal guts. Scientists have also discovered a way to produce phosphine through artificial chemical reactions. The ALMA (Atacama Large Millimeter/submillimeter Array) showed a weak signal at the spectral line, which is the frequency that phosphine molecules in Venus's atmosphere typically absorb energy. Scientists have concluded that some form of metabolism or a chemical process would be the only explanation for the high amounts of phosphine gas in Venus's atmosphere. Metabolism is a process that maintains a living organism, so the possibility that the phosphine was a result of metabolism implies the presence of life. This premature conclusion set an optimistic tone for the rest of the study.

Venus's conditions are not ideal for making phosphine molecules on their own, which further suggests that some form of life must be producing this phosphine. This conclusion seems unexpected due to Venus's extreme temperatures. However, scientists have ruled out other possible explanations for the presence of phosphine. Soon after the initial discovery study was published, the results of three additional independent studies have challenged this discovery and claimed that there is no evidence of phosphine in Venus's atmosphere. One of the independent research teams used archived data from 2015 by NASA's Infrared Telescope Facility in Hawaii. The team concluded that this data does not support the claim that phosphine is present in Venus's atmosphere. The other two independent research teams looked at the data obtained in the study in question. After reprocessing the data, neither of the teams could confidently conclude phosphine's presence in Venus's atmosphere. One of the independent research teams that looked at the data from JCMT (James Clerk Maxwell Telescope) explained that the spectral line suggestive of phosphine could have been sulfur dioxide gas, which has previously been confirmed to be present on Venus.

Additionally, the ALMA was discovered to have been calibrated incorrectly in the initial study, making the recorded data more challenging to use. These independent research teams are also questioning the accuracy of the initial study's data processing, suggesting possible false signals. Both teams concluded that the data was not sufficient to infer the presence of phosphine confidently.

Water on Mars?

Water is vital for survival. Numerous studies suggest that Mars was covered in rivers, lakes, and seas billions of years ago, suggesting that Mars's atmosphere was dense enough to retain heat and keep the water in liquid form. Scientists have indicated that Mars' past water content could be a sign of life in the past and possibly the present. A team of Italian researchers reported the discovery of a buried lake using the Mars Express's MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding). MARSIS emits radio waves that bounce off the planet's surface and subsurface, reflecting a signal that reveals the material present in that area. Initially, the MARSIS was inconsistent in detecting bright reflections, which could have been water. Scientists could resolve this problem using the raw data collected rather than the machine's pre-processed data. Scientists were then able to rule out other explanations for these bright areas to conclude that the reflections were indeed a sign of water.

The conclusion was based on 29 observations made between 2012 and 2015. Many scientists were skeptical to accept the conclusion, explaining that more evidence is needed to confirm the lakes' presence. New research published September 28, 2020, done in the same area using data from MARSIS, confirmed the 2018 finding and found three additional lakes. This study used 134 observations made between 2012 and 2019. Microbial life has been found in subglacial lakes similar to this one on Earth; however, the lakes on Mars have an exceptionally high salt content. Scientists have concluded that there is not enough heat on Mars to keep the water in the lake's liquid, so the lakes must be salty. Life can be sustained in environments with a salt content five times that of sea-water; however, these lakes seem to be well above that threshold, leading some to believe that they could not support any life. This research was met with skepticism once again, suggesting that the data is incorrect and that the bright spots are some other substance.

Image Created by Joey Serricchio


Regardless of phosphine's presence on Venus or water on Mars, this research demonstrates a fundamental part of scientific research.

The initial studies for both planets incited some controversy, followed by other research teams and scientists suggesting that there was not enough evidence to support either conclusion strongly. Regardless of which team is right in this situation, this research still provides a valuable takeaway: science is about collaboration, self-correction, and innovation, and is inherently a try, fail, and try again process. Other researchers scrutinized initial discoveries, who identified flaws and suggested that their conclusion was not supported by evidence. This cycle is what distinguishes science from other disciplines: there is almost always an opportunity to build upon, expand on, or disprove a discovery. Science is an ever-growing field that will continue to flourish as discoveries are made, questioned, and confirmed.

So, when will we be sure?

Scientists researching Venus are waiting on new data and conclusions to be peer-reviewed to make a final, strongly supported conclusion. They are utilizing technology to communicate and collaborate. They are cautiously optimistic they will find a logical conclusion on whether phosphine is present or not soon.

Scientists researching Mars are continuing their research. A Chinese mission called Tianwen-1 mission is set to deploy a rover on the surface of Mars in February of 2021, which could provide more evidence for or against the possibility of water on Mars.


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