Jim Green joined NASA in 1980. He helped the space agency understand the Earth's magnetic field, explore the outer solar system and search for life on Mars. He bade farewell to the agency as the new year arrived.
Over the past four decades, which includes 12 years as the director of NASA's planetary science division and the last three years as its chief scientist, he has shaped much of NASA's scientific inquiry, overseeing missions across the solar system and contributing to more than 100 scientific papers. He specialized in Earth's magnetic field and plasma waves early in his career, but went on to do other research.
The confidence of life detection, or CoLD, scale is one of the most significant proposals by Dr. Green. He has published work that suggests we could terraform Mars, or make it hospitable for humans, by using a giant magnetic shield to stop the sun from stripping the red planet's atmosphere. He is a big fan of the exploration of other worlds, including a mission to the icy moon of Jupiter.
Dr. Green spoke about some of the work he was doing ahead of the December meeting of the American Geophysical Union. The excerpts from our interview have been edited.
You have urged a methodical approach to looking for life with your CoLD scale, ranking possible detections from one to seven. Why do we need a scale?
Scientists said they had seen phosphine in the atmosphere of Venus. They believed life was one of the major possibilities because they saw it at such a high level. On the CoLD scale, seven is "we found life" and one is "one". It didn't make it to two. They realized there was a problem with their signal and it may not be phosphine. We need to do a better job of communicating.
There is methane on Mars. The majority of methane we find here on Earth comes from life. We are only at a CoLD Level 3, but if a scientist came to me and said, "Here's an instrument that will make it a CoLD Level 4," I would fund that mission in a minute. They are not jumping to seven because they are making the next step to find life in the solar system. We have to stop messing around with just crying wolf.
The search for life on Mars has been a focus of NASA for over 30 years. We haven't found life in that time, are you surprised?
Yes and no, what we are doing now is much more methodical, much more intelligent, and we are able to recognize what signatures life can produce over time. Earth is covered in life because our solar system is 4.5 billion years old. We would find out that Venus was a blue planet if we went back a billion years. There was a significant ocean. It could have had a lot of life. Mars is a blue planet if we go back another billion years. Mars went stagnant about 3.5 billion years ago, after it lost its magnetic field.
We would have liked to have found life on the surface. We put the Viking landers in a bad place because we didn't know where to put them. It felt like putting something down in the desert. We should have put them down in Jezero Crater, but we didn't know it existed at the time.
We couldn't say we found life because only one of the three instruments did, but one of the Viking experiments indicated there was life in the soils. We are going to bring back samples. It would need a sample return mission.
You have suggested that a giant magnetic shield between the planet and the sun could be placed to stop the sun from stripping the atmosphere of Mars, which would allow the planet to trap more heat and warm its climate to make it habitable. Is that doable?
It is doable. The pressure is going to increase if the stripping is stopped. Mars is going to terraform itself. We want the planet to be involved in this in any way it can. The temperature goes up when the pressure goes up.
The first level of terraforming is 60 bars, a factor of 10 from where we are now. If you walk out on the surface, your blood won't boil. You could have more flexibility and mobility if you didn't need a spacesuit. The higher the temperature and pressure, the more plants will grow in the soil.
There are several ways to do the magnetic shield. I have been working on a paper for two years. It is not going to be well received. The idea of terraforming is not popular with the planetary community. You know. I believe we can change Venus with a shield that reflects light. The temperature starts going down when we create a shield.
NASA approved the mission to search for signs of life on Jupiter's moon, called the Europa Clipper, in 2015, following the detection of a large amount of water in the ocean. Did you want to see it happen sooner?
I would have liked to have seen it earlier, but it wasn't going to happen. There are some missions that are so large they are called strategic missions. The stars have to align for them to happen. You have to propose it, have a solid case work, and then pitch it to Congress. I proposed a mission every year. Every year. The administration did not want to go to Europe.
The mission was made possible by the plumes on Europa. I was at a meeting of the American Geophysical Union. Several scientists were going to give a talk about finding a Hubble image on a planet, and I exclaimed, "Oh, my God." I want to do a press conference. They pulled it off when I called back to NASA headquarters. I added that information to the story of Europa. That turned the corner. They exclaimed, "Maybe we should do this."
The Congress decided against putting a lander on the mission. Did you want one?
I would love to have a lander, but it is not in the cards. The mission is too complicated, but everything we do on Clipper feeds into a lander. I insisted that we had a high-resolution imager to the point, so that we could get the information we needed to land safely. If we don't get high-resolution images, we'll never be able to land.
You want to take a small step. You fail when you do that. We took too big a step in Viking. We didn't know where to go, we didn't know enough about the soils. We didn't know where water was in the past. We should have known about 10 things before putting the two Vikings on the surface.
Are you going to work on scientific papers in retirement?
Absolutely. I have the Mars paper to do. I have a paper I want to write. I have a book I am working on. I have a passion for science.
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A guide to the craft.
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