InSight's revelation on Mars’ rotation

Episode Summary

Executive Summary: This Planetary Radio episode weaves together three themes: new science from Mars InSight data showing Mars’ rotation is slightly accelerating and its core is liquid but unusually shaped; advocacy and policy work centered on Planetary Society Day of Action and the future of Mars Sample Return; and human-interest updates from an annular eclipse, OSIRIS-REx sample opening, and upcoming observing opportunities. The show closes with a playful but informative note on the naming of NASA’s Lucy mission and asteroid exploration.

Main Topics: Mars InSight/RISE reveals Mars rotation and deep interior details: Sébastien Lamaester explains how radio tracking from the InSight lander’s RISE instrument measured tiny changes in Mars’ rotation, constraining the size and shape of the core and finding evidence for a liquid core. The team also found no detectable signature of a solid inner core in the current data. Mars is speeding up slightly: The transcript highlights the headline result that Mars’ spin appears to be accelerating by a tiny amount. Several possible causes are discussed, including polar ice redistribution, planetary shape changes, tidal effects, and impacts, but no definitive explanation is yet established. OSIRIS-REx sample return and the excitement of sample science: Amber Trujillo describes attending the opening of the OSIRIS-REx sample return capsule and the emotional response from the mission team. The discussion emphasizes how asteroid samples can inform theories of solar system formation and the origin of life. Planetary Society Day of Action and space policy advocacy: Jack Kirali summarizes the return of the Planetary Society’s in-person Day of Action, with members meeting lawmakers to advocate for balanced planetary science funding. The segment stresses support for Mars Sample Return, Dragonfly, VERITAS, NEO Surveyor, and research funding. Mars Sample Return status and strategic importance: Kirali explains that an independent review board did not recommend canceling Mars Sample Return, but urged NASA to redesign for better cost control and resilience. The mission remains the top priority of the planetary science community and a key precursor to future human Mars exploration. Community, eclipses, and public engagement with astronomy: The episode includes reflections on the annular eclipse, International Observe the Moon Night, and how space events inspire curiosity, especially in young people and the public at large.

Key Arguments: InSight’s RISE data can detect extremely small rotational changes in Mars, enabling constraints on interior structure that were not accessible from earlier missions. Mars’ core is confirmed to be liquid, and its shape appears closer to a hydrostatic equilibrium than expected, adding new complexity to interior models. The observed rotational acceleration is real enough to appear in multiple analyses, but its cause remains unresolved and may involve mass redistribution rather than a single simple explanation. OSIRIS-REx demonstrates the scientific value of sample return, especially for studying water, carbon compounds, and prebiotic chemistry relevant to life’s origins. Planetary Society advocacy matters because congressional support directly affects the future of planetary science missions and balanced NASA funding. Mars Sample Return should continue because it is a top decadal priority, an international partnership, and a necessary step toward future human missions to Mars. The amount of NASA funding is small relative to the federal budget, so planetary science yields outsized scientific and strategic value for a relatively modest public investment.

Data Points: Mars rotational change: about 40 centimeters over a Martian year - The tiny surface motion RISE had to detect to infer deep interior dynamics. Acceleration rate: about one microsecond per year - Approximate magnitude of Mars’ spin-up discussed by Sébastien Lamaester. InSight launch date: May 2018 - NASA’s InSight mission launched to Mars in 2018. InSight landing date: November 2018 - InSight landed on Mars later in 2018. Mission end: December 2022 - InSight’s mission officially ended in 2022. Paper publication: Nature, earlier in 2023 - The RISE team’s paper 'Spin State and Deep Interior Structure of Mars from InSight Radio Tracking' was published in Nature. Day of Action meetings: 164 meetings - Planetary Society members and supporters held meetings with lawmakers during the 2023 Day of Action. States represented: 36 states - The 164 meetings covered legislators representing over 36 states. In-person participation: over 100 members - Members participated in the in-person Day of Action in Washington, D.C. Virtual participation: over 300 people - Additional supporters participated virtually by writing to Congress. NASA budget share: about 0.5% of the federal budget - Used to illustrate that NASA’s budget is small relative to total U.S. federal spending. Mars Sample Return architecture: 3 missions in 1 - Described as a lander, Mars ascent vehicle, and Earth return orbiter. Mars geologic history: 3.7 billion years - The samples could reveal roughly 3.7 billion years of Martian geologic history. Delay in Mars communications: 46 minutes - Used to explain why Mars sample return systems must operate autonomously. LightSail 2 duration: more than 3 years - Bill Nye notes LightSail 2 operated from June 2019 to November 2022. LightSail 2 mission dates: June 2019 to November 2022 - The spacecraft used sunlight to change its orbit around Earth.

Pivotal Quotes: "democracy is not a spectator sport. It involves showing up." — Jack Kirali: Explaining the purpose and civic value of the Planetary Society’s Day of Action. "Mars sample return is that precursor mission to future human missions." — Jack Kirali: Describing why the mission matters beyond scientific return alone. "we needed a lot of time to accumulate a lot of data because we want to see arising from the noise. The signature of the deep interior." — Sébastien Lamaester: Explaining the sensitivity and patience required for the RISE radio-tracking measurements.

Implications: Mars science is entering a precision era, while advocacy and public engagement remain crucial to keeping major missions alive. The episode suggests that sample return and sustained funding will shape future Mars exploration and life-detection efforts.