Throughout his career spanning four decades, which includes serving as the director of NASA’s planetary science division for 12 years and its chief scientist for the past three years, he has played a significant role in shaping NASA’s scientific research. He has overseen missions throughout the solar system and has contributed to more than 100 scientific papers covering various topics. While initially focusing on Earth’s magnetic field and plasma waves, he has expanded his research interests over time. One of his recent notable contributions is the development of a scale called the “confidence of life detection,” or CoLD, for verifying the discovery of alien life. Additionally, he has proposed the idea of using a giant magnetic shield to terraform Mars and make it suitable for human habitation by preventing the sun from stripping away the planet’s atmosphere and increasing surface temperatures. He has also been a strong advocate for exploring other worlds, such as planning a mission to Europa, Jupiter’s icy moon, set to launch in 2024. Before a meeting of the American Geophysical Union in New Orleans in December, Green discussed his extensive work and the exploration for life within our solar system. Below are excerpts from our interview, edited and condensed. Green has advocated for a systematic approach to detecting life with the CoLD scale, which categorizes potential discoveries on a scale of one to seven. This scale is necessary because a few years ago, researchers claimed to have identified phosphine in Venus's atmosphere. They observed the possibility of life at a significant level, although it did not reach the level of certainty. They later realized there was contamination in their signal and it might not be phosphine after all. Communication improvements are needed. Methane is prevalent on Mars, and while most methane on Earth comes from life, there is a small percentage that does not. We are currently at CoLD Level 3, but if a scientist presented an instrument that could elevate us to CoLD Level 4, I would immediately support that mission. Progress towards finding life in the solar system is important, and we need to stop delaying and take the necessary steps to achieve this goal. Despite NASA's focus on searching for life on Mars since the 1970s, including missions like Viking 1 and 2 and later missions, it is surprising that we have not yet found life on the planet. Response A: Our current approach to identifying signs of life is more systematic and informed compared to the past. The Earth has been teeming with life for billions of years, but looking back a billion years, Venus had a large ocean and was a blue planet. It is possible that Mars once supported life in abundance, as it was a blue planet over a billion years ago. However, Mars lost its magnetic field, causing water to evaporate and the planet to become stagnant around 3.5 billion years ago. Despite this, there is still hope of finding evidence of life on Mars. The Viking landers were placed on the surface without much consideration, as scientists were simply trying to land them on Mars. It felt as though we were leaving something behind in the vast Gobi Desert. We should have left them in Jezero Crater, where we are currently with the Perseverance rover, but we were unaware of its existence at that time. One of the Viking experiments suggested the presence of microbial life in the soil, but only one of the three instruments confirmed it, so we were unable to confirm the discovery of life. Now, with the plan to bring back samples, we will finally have definitive answers. The need for a sample return mission was unexpected. Question: In the past, you have proposed the idea of using a large magnetic shield to prevent the sun from stripping Mars' atmosphere, allowing the planet to retain more heat and become habitable. Is this idea feasible?
Answer: Yes, it is feasible. By preventing the sun from stripping the atmosphere, the pressure on Mars will increase, leading to the planet starting to terraform itself. We desire for the planet to be involved in this process in any way possible. As the pressure increases, so does the temperature. The initial stage of terraforming occurs at 60 millibars, which is ten times higher than our current level. This is known as the Armstrong limit, where a person's blood would not boil if they were to walk on the surface without a spacesuit. Without the need for a spacesuit, there would be greater freedom of movement and flexibility. Paraphrased Text = The increased temperature and pressure allow for the initiation of plant growth in soil. Various methods for creating a magnetic shield are being considered. I am currently finalizing a research paper that I have been working on for approximately two years, although I anticipate it will not be well-received. The planetary community is generally opposed to the concept of terraforming. I believe we have the ability to alter Venus by using a physical shield that reflects light, which would lower the temperature. The Europa Clipper mission, approved by NASA in 2015 to search for signs of life on Jupiter's moon Europa, is set for launch in 2024 after plumes were detected erupting from its subsurface ocean in 2013. Would you have preferred for this mission to happen sooner? Text = A: I wish I could have seen it earlier, but it was not possible. There are certain missions that are very large and are considered strategic missions. In order for them to happen, everything needs to fall into place. You have to submit a proposal, have a strong case, present it to NASA administration, and then pitch it to Congress. Every year, I proposed a Europa mission. Each year, the administration showed no interest in visiting Europa. It was the discovery of plumes on Europa that ultimately led to the Europa mission. In 2013, at an American Geophysical Union meeting, several scientists were set to present their findings on detecting a plume with Hubble on Europa. This news excited the speaker, prompting them to want to hold a press conference. I contacted NASA headquarters again, and they successfully completed the task. I brought that information back to headquarters and incorporated it into the Europa story, which made a significant impact. This led them to consider the idea of doing something similar. When asked about Congress's decision not to include a lander on the mission, I was in favor of having one. A: While a lander would be great, it's not currently part of the plan. Adding a lander would complicate the mission, but our work on Clipper is laying the groundwork for a future lander. I emphasized the importance of having a high-resolution imager so that we can gather the necessary information to safely choose a landing spot as we fly over certain areas. Europa has dangerous terrains, so without this imaging, landing would be impossible. It's important to take measured steps forward rather than taking a huge leap, as that often leads to failure. Viking serves as an example of when we made a mistake by taking a large step without enough knowledge. We didn't have enough information about the soils or toxins, and we didn't have a clear understanding of the planet's water sources in the past before sending the two Vikings to the surface. There were 10 important things that we should have known beforehand. The question is whether you will continue working on scientific papers in your retirement. A: Certainly. I am currently working on a paper about Mars, another one about Europa, and I am also writing a book on astrobiology. My enthusiasm for science is unquenchable. Copyright 2022 by The New York Times Company.