Over the last 40 years, including 12 years as the director of NASA's planetary science division and the past three years as its chief scientist, he has been influential in shaping NASA's scientific research by overseeing missions throughout the solar system and contributing to over 100 scientific papers on various topics. Initially focusing on Earth's magnetic field and plasma waves, he later diversified his research interests. One of his recent significant contributions is the development of a scale called the "confidence of life detection" (CoLD) for verifying the discovery of alien life. He has also proposed using a giant magnetic shield to make Mars habitable for humans by preventing the sun from stripping away its atmosphere and raising surface temperatures. Additionally, he has advocated for the exploration of other planets, including a planned mission to Jupiter's icy moon Europa in 2024. Before a December conference of the American Geophysical Union in New Orleans, Green discussed his diverse research and the exploration for life within our solar system. The following are edited and summarized highlights from our conversation. Green emphasized the importance of a systematic method of searching for life, as demonstrated by his CoLD scale which categorizes potential findings on a scale of one to seven. This approach was prompted by the announcement of the detection of phosphine in Venus' atmosphere by scientists a few years ago. Seen at a massive scale, they were initially optimistic about the potential for life. However, upon further analysis, it was determined that their findings were inconclusive and likely contaminated. While methane is prevalent on Mars, it is not necessarily a definitive indicator of life. 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 fund that mission. Rather than jumping to level seven, we need to take the next significant step towards finding life in the solar system. It is essential to stop wasting time and resources on false alarms and focus on making real progress. The search for life on Mars has been a priority for NASA since 1976, starting with the Viking 1 and 2 landers and continuing with missions in the 1990s. Despite this long history, it is not surprising that we have not yet found life on Mars. Response = A: Our current approach is more systematic and intelligent in identifying the signs of life that can develop over time. Earth, which is now teeming with life, has been around for 4.5 billion years. Looking back a billion years, Venus used to be a blue planet with a large ocean. It is possible that Mars once had abundant life, as it was a blue planet a billion years ago. However, Mars eventually lost its magnetic field, causing water to evaporate and the planet to become stagnant around 3.5 billion years ago. Despite our attempts to search for life on the surface with the Viking landers, they were placed in a random location due to our lack of knowledge about Mars. It was comparable to placing an item in the Gobi Desert. We should have placed them in Jezero Crater, where we are currently located with the Perseverance rover, but we were unaware of its existence at the time. One of the Viking experiments suggested the presence of microbial life in the soil, but only one of the three instruments confirmed this, so we were unable to conclusively say that we had discovered life. With the upcoming sample return mission, we will finally have concrete evidence. We had not anticipated the need for a sample return mission. Question: In the past, you have mentioned the idea of using a large magnetic shield to protect Mars from the sun's atmosphere-stripping effects, potentially allowing the planet to warm up and become habitable. Is this plan feasible? 
Answer: Yes, it is feasible. By preventing the atmosphere from being stripped away, Mars would naturally begin to terraform itself as the pressure increases. We desire for the planet to be involved in any way possible. As pressure increases, so does temperature. The initial stage of terraforming occurs at 60 millibars, which is 10 times higher than our current level. This threshold is known as the Armstrong limit, where one's blood would not boil if they were to walk on the surface without a spacesuit. Eliminating the need for a spacesuit would greatly enhance flexibility and mobility. Paraphrased Text = The increased temperature and pressure make it possible to start cultivating plants in the soil. Various methods for creating a magnetic shield are being considered. I am in the process of finalizing a research paper that I have been working on for the past two years. However, I anticipate that it will not be well-received, as the planetary community is generally opposed to the concept of terraforming. I believe that we have the ability to alter Venus by using a physical shield that reflects light, which would help lower the temperature. In 2015, NASA approved the Europa Clipper mission to explore Jupiter's moon Europa for signs of life. The mission is scheduled for launch in 2024 after plumes were detected erupting from the moon's subsurface ocean in 2013. Would you have preferred for this mission to happen sooner? A: Yes, I would have liked to have seen it earlier, but it was not possible. There are specific sets of missions that are so large they are referred to as strategic missions. In order for them to occur, everything has to fall into place. You must 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. The discovery of plumes on Europa sparked the Europa mission. In 2013, at an American Geophysical Union meeting, several scientists planned to discuss finding a plume using Hubble on Europa. Excited by this news, the speaker expressed a desire 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 narrative of Europa. This was a pivotal moment that sparked interest. The response was positive, with some suggesting the possibility of pursuing the idea. When asked about Congress's decision to not include a lander on the mission, the response was neutral. A: Although I would like to have a lander, it is not currently feasible. Adding a lander would complicate the mission, but everything we are doing on Clipper is helping to pave the way for a future lander mission. I made sure that we included a high-resolution imager so that when we fly over certain areas, we will have the necessary information to identify safe landing spots. Europa has some dangerous terrains, so without high-resolution imaging, landing would be impossible. It is important to take small steps rather than big ones, as taking on too much at once can lead to failure. Viking serves as an example of when we made a large leap without enough knowledge. We were unsure of where to go, lacked understanding of the soils and toxins, and had limited information about water on the planet. There were 10 crucial things we should have known before sending the two Vikings to the surface. The question remains: Will you continue to work on scientific papers during your retirement? Paraphrased text = A: Yes, definitely. I am currently working on a paper about Mars. I am also in the process of writing a paper about Europa. Additionally, I am working on a book about astrobiology. My passion for science is unquenchable. Copyright 2022 by The New York Times Company.