MESSENGER Sails by Mercury for a Second Flyby

Episode Summary

Executive Summary: This Planetary Radio episode centers on MESSENGER’s successful second Mercury flyby, highlighting new global images, surface spectroscopy, topography, magnetic-field measurements, and an unexpected demonstration of solar sailing. The show also features Planetary Society leadership news, a Mars orbiter comparison Q&A, and Bruce Betts’ astronomy update, trivia, and contest announcements.

Main Topics: MESSENGER’s second Mercury flyby: Sean Solomon details the spacecraft’s close encounter, including high-resolution imaging, color observations, altimetry, and early science return from the October 6 flyby. Mercury science findings: Discussion of Mercury’s surface features, exosphere, sodium tail, and magnetic environment, including surprising ray patterns and multi-species atmospheric escape. Solar sailing as a navigation tool: MESSENGER used solar radiation pressure to make trajectory corrections without propellant, achieving more accurate targeting than prior flybys. Planetary Society leadership and outreach: Bill Nye announces Jim Bell as the new president of the Planetary Society board and frames it as part of the society’s push to engage younger and more global audiences. Mars orbiter comparison Q&A: Emily Lakdawalla explains how Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Express differ in resolution, orbit, radar capability, and communications role. Night sky, trivia, and contest news: Bruce Betts covers visible planets, space history, Chandrayaan-1, trivia results, and new prize details for an upcoming Planetary Radio contest.

Key Arguments: MESSENGER returned a rich dataset from its second Mercury flyby, with more than 1,200 images and complementary spectroscopy, altimetry, and magnetic-field measurements. The bright ray crater near Mercury’s north pole has unexpectedly far-reaching ejecta, extending nearly to the opposite side of the planet. Mercury’s neutral tail is not just sodium-based; new observations suggest it contains multiple species, including calcium, so it should be renamed. Solar sailing is not merely theoretical: MESSENGER used solar radiation pressure to improve navigation and hit its aim point more accurately than on previous flybys. The Planetary Society is intentionally refreshing its leadership and outreach by elevating Jim Bell, a long-time member, to help engage younger and more international audiences. Mars orbiters are differentiated by mission design, not just instruments: Odyssey provides global mapping, MRO focuses on high-resolution targeted imaging, and Mars Express uses an elliptical orbit for unique viewing opportunities.

Data Points: MESSENGER images returned: more than 1,200 - Sean Solomon on the second Mercury flyby Mercury surface imaged by MESSENGER: about 95% - Sean Solomon describing cumulative global coverage Area first seen in close-up: bigger than the land area of South America - Sean Solomon on the flyby’s target region Number of color filters used: 11 - High-resolution color imaging during departure from Mercury Mercury sodium tail extent: at least 1,000 radii - Earth-based observations referenced by Sean Solomon Planned Mercury orbit insertion: 18 March 2011 - Sean Solomon describing mission timeline Next Mercury flyby date: 29 September 2009 - Sean Solomon discussing future mission events Planetary Society trivia cutoff: Monday, October 27 at 2 p.m. Pacific time - Bruce Betts announcing contest deadline Deep Space One anniversary: 10th anniversary - Bruce Betts on space history Mercury-sized objects fitting into Earth (crushed): 17.88 - Trivia answer cited during the contest segment Mercury-sized objects fitting into Earth (uncushed): 7 - A listener’s alternate answer noted by Bruce Betts

Pivotal Quotes: "We took over 1,200, but that shot... was the first image that we sent down from the spacecraft." — Sean Solomon: Describing the first major image from MESSENGER’s second Mercury flyby "the team... became so skilled at using radiation pressure... that... we hit our aim point more accurately than in any of our previous flybys." — Sean Solomon: Explaining how solar sailing improved navigation precision "The society is getting younger." — Bill Nye: Announcing Jim Bell as the new president of the Planetary Society board

Implications: MESSENGER’s flyby showed that early mission operations can yield transformative science and even save propellant through solar sailing. For listeners, it highlights Mercury as an active, complex world and signals growing public engagement in planetary exploration and society leadership.