John Batchelor Hotel Mars with Dr. Simone Marchi, Wednesday, 7-2-25

John and I welcomed Dr. Marchi from the SWRI in Boulder, CO to discuss his work pertaining to "The shaping of terrestrial planets by late accretions." You can review his Nature Review paper at https://www.nature.com/articles/s41586-025-08970-8. Briefly, he and his co-author examine the "disproportionate role of the last approximately 1% of planetary growth, or late accretion, in controlling the long-term evolution of the Earth and other terrestrial planets. Late accretion may have been responsible for shaping Earth’s distinctive geophysical and chemical properties and generating pathways conducive to prebiotic chemistry." During our discussion with Dr. Marchi he explained why the last 1% was so vital in the formation of Venus, Mars and Earth. Also Mercury but his comments on Mercury were a bit different. We talked about impacts being similar in nature but since each rocky planet was different, the consequences of the impacts were different. He said they were random, atmospheres made a difference and even shaped some of the consequences. Don't miss his comments about the dinosaurs and their extinction event, the role of luck, and the fact that we need to be looking for exoplanets not just for an Earth twin but also a similar impact history to Earth. When asked about our TRL for being able to do that, well, we have much to learn. In the second half John asked his usual question about having an unlimited budget. don't miss what he had to say about Venus as a priority in this four minute segment. Read the full version of this summary at www.thespaceshow.com and doctorspace.substack.com.