The Space Show by Dr. David Livingston Hotel Mars with Dr. Simone Marchi on the last 1% of planet growth for Earth & others and why it matters.
John and I had the pleasure of welcoming Dr. Simone Marchi from the Southwest Research Institute (SWRI) in Boulder, CO, to discuss his recent work on “The shaping of terrestrial planets by late accretions.” You can read his paper, published in Nature, at: https://www.nature.com/articles/s41586-025-08970-8.
In this fascinating study, Dr. Marchi and his co-author explore how the final ~1% of planetary growth—known as late accretion—may have played a disproportionate role in the long-term evolution of Earth and other terrestrial rocky planets, including Mercury, Venus and Mars. Their research suggests that late accretion may have significantly influenced Earth’s and the other rocky planets unique geophysical and chemical traits and may even have created conditions favorable for prebiotic chemistry.
During our conversation, Dr. Marchi elaborated on why this last 1% of growth was so critical for the development of Venus, Mars, and Earth. His comments on Mercury offered a slightly different perspective so don't miss them. While impact events were broadly similar across the rocky planets, their outcomes varied dramatically due to differences in planetary characteristics such as size, composition, and atmosphere. He emphasized the randomness of these events, the role of atmospheric conditions, and how those factors shaped the consequences of impacts. I asked our guest if he ever considered the events not being random. He said yes but he deals with the physics, not other possible realms.
Don’t miss his thoughts on the dinosaur extinction event, the role of chance in planetary history, and his compelling argument for why the search for exoplanets should go beyond finding Earth twins—we must also consider planets with impact histories similar to Earth’s. When asked about our current Technology Readiness Level (TRL) for making such assessments, he acknowledged that there’s still a great deal to learn.
In the second half of the discussion, John posed his signature question: What would you do with an unlimited budget? Dr. Marchi’s response was compelling—especially his case for making Venus a top exploration priority. This four-minute segment is definitely worth a listen.
Special thanks to our sponsors:Northrup Grumman, American Institute of Aeronautics and Astronautics, Helix Space in Luxembourg, Celestis Memorial Spaceflights, Astrox Corporation, Dr. Haym Benaroya of Rutgers University, The Space Settlement Progress Blog by John Jossy, The Atlantis Project, and Artless Entertainment
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UPCOMING PROGRAMS:
Guests:Dr. David Livingston
No program today as part of the July 4th holiday weekend.
Our next programming begins Tuesday, July 8 with Steven Benner on the Viking Mission life experiments. Listening details will be available for this program on our Upcoming Program Menu on the right side of our home page, www.thespaceshow.com by Monday, July 7, 2025.
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