James L. Green

Over a 42-year career at NASA, James L. Green rose from hands-on space physicist to Director of the Planetary Science Division and ultimately NASA’s Chief Scientist.

In those roles, he carried overall responsibility for more than 30 space missions and helped deliver some of the most significant moments in modern exploration. These include the first close-up images of Pluto from New Horizons, the insertion of Juno into orbit around Jupiter, and the landing of the Curiosity rover on Mars.

As Chief Scientist, Green helped set NASA’s scientific priorities across planetary science, heliophysics, Earth observation and human spaceflight. He also played a central role in planetary defence and coordinated NASA’s scientific input to The Martian, ensuring that Hollywood fiction stayed grounded in real physics.

What makes Green particularly relevant today is his deep understanding of how space affects the human body and why that matters for health and ageing on Earth. In microgravity, processes that normally unfold over decades, such as muscle loss, bone density reduction and cellular stress, occur in weeks. For scientists, this creates a powerful natural laboratory. Green has spent years working with biologists and medical researchers to understand what these accelerated changes reveal about cellular resilience, mitochondrial function and ageing itself.

Since retiring from NASA in 2022, James Green has focused on applying these insights beyond the space programme. He works with research teams, including collaborators at the University of Oxford, and advises health and diagnostics companies on how space-derived science can inform evidence-based approaches to longevity, wellness and precision medicine. His value lies in decades of observing how the human body responds under extreme conditions and knowing which lessons are transferable.

James Green has authored more than 125 peer-reviewed scientific papers, received NASA’s Distinguished Service Medal, and had an asteroid — 25913 Jamesgreen — named in his honour. He was the long-running host of Gravity Assist, a NASA podcast that took listeners inside major missions and scientific debates, speaking plainly with astronauts, engineers and policymakers. He now teaches planetary science to students around the world, including in immersive digital environments.