(p. D5) Since joining NASA in 1980, Jim Green has seen it all. He has helped the space agency understand Earth’s magnetic field, explore the outer solar system and search for life on Mars. As the new year arrived on Saturday, he bade farewell to the agency.
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 across a range of topics. While specializing in Earth’s magnetic field and plasma waves early in his career, he went on to diversify his research portfolio.
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Ahead of a December  meeting of the American Geophysical Union in New Orleans, Dr. Green spoke about some of this wide-ranging work and the search for life in the solar system. Below are edited and condensed excerpts from our interview.
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You’ve previously suggested it might be possible to terraform Mars by placing a giant magnetic shield between the planet and the sun, which would stop the sun from stripping its atmosphere, allowing the planet to trap more heat and warm its climate to make it habitable. Is that really doable?
Yeah, it’s doable. Stop the stripping, and the pressure is going to increase. Mars is going to start terraforming itself. That’s what we want: the planet to participate in this any way it can. When the pressure goes up, the temperature goes up.
The first level of terraforming is at 60 millibars, a factor of 10 from where we are now. That’s called the Armstrong limit, where your blood doesn’t boil if you walked out on the surface. If you didn’t need a spacesuit, you could have much more flexibility and mobility. The higher temperature and pressure enable you to begin the process of growing plants in the soils.
There are several scenarios on how to do the magnetic shield. I’m trying to get a paper out I’ve been working on for about two years. It’s not going to be well received. The planetary community does not like the idea of terraforming anything. But you know. I think we can change Venus, too, with a physical shield that reflects light. We create a shield, and the whole temperature starts going down.
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(Note: ellipses, and bracketed year, added.)
(Note: the online version of the story has the date Jan. 2, 2021, and has the title “NASA’s Retiring Top Scientist Says We Can Terraform Mars and Maybe Venus, Too.” The first three paragraphs, and the block-indented sentence and question, are by the interviewer Jonathan O’Callaghan. The answer after the question is by Jim Green.)