Astonishing Mercury, With MESSENGER Principal Investigator Sean Solomon

Episode Summary

Executive Summary: This episode centers on MESSENGER’s first Mercury flyby, highlighting surprising evidence of water-related ions, confirmation of widespread volcanism, and stronger support for Mercury’s cooling and contraction. It also covers Pluto’s new dwarf-planet-style nomenclature debate, Mars Odyssey’s continued utility as a Mars relay, and a skywatch segment with eclipses, planets, and the Perseids.

Main Topics: MESSENGER’s Mercury flyby: water-related ions: Sean Solomon explains that MESSENGER detected ionized fragments associated with water molecules in Mercury’s exosphere, an unexpected finding that raises questions about whether the source is polar ice, cometary delivery, or solar-wind interactions. Mercury’s volcanism versus impact origins: The discussion revisits the long-standing debate over Mercury’s smooth plains and explains that MESSENGER imaging found volcanic-looking centers and deposits, strongly supporting volcanic activity on Mercury. Mercury’s contraction and interior cooling: New thrust faults seen by MESSENGER reinforce the idea that Mercury has shrunk as its large core cools and its inner core solidifies, helping explain the planet’s tectonic history and magnetic field. Pluto naming and classification debate: Bill Nye jokes about Pluto’s status, arguing against the IAU’s dwarf-planet framing and celebrating the naming of Plutoids as a way to preserve Pluto’s iconic status. Mars Odyssey’s future as a Mars relay: Emily Loctawala explains that Odyssey remains scientifically useful and is critical as a communications relay for Mars surface missions, with fuel unlikely to end its service anytime soon. Night sky update and eclipse season: Bruce Betts previews an upcoming total solar eclipse, a partial lunar eclipse, Jupiter’s prominence, Saturn-Mars pairing, and the Perseid meteor shower, while also noting Apollo 11’s anniversary and a lunar trivia contest.

Key Arguments: MESSENGER dramatically advanced Mercury science because 11 Science papers followed the first flyby, the most since Mariner 10’s 1970s visits. The detection of water-group ions suggests Mercury may contain or interact with water-related material, but the origin remains unresolved. Polar permanently shadowed craters may trap ice, making Mercury’s poles a key target for future MESSENGER observations. MESSENGER found volcanic landforms that resemble lunar volcanic centers, supporting the idea that many Mercury plains are volcanic rather than impact-generated. The abundance of thrust faults indicates Mercury contracted more than previously estimated, likely as its large core cooled and its inner core solidified. Mars Odyssey can continue operating for years because its fuel use is very low and it remains essential for data relay from surface missions. Pluto’s reclassification is presented as a naming dispute more than a scientific crisis, emphasizing the emotional attachment people have to the word planet.

Data Points: Science papers on Mercury: 11 papers - Published together after MESSENGER’s first Mercury flyby Time since Mercury was last revisited up close: 33 years - Between Mariner 10 and MESSENGER’s January flyby Closest flyby altitude: 200 kilometers - MESSENGER’s first flyby over Mercury’s surface Previously unseen Mercury surface area imaged: 20% - New terrain seen during MESSENGER’s January flyby Additional Mercury area to be seen on next flyby: 30% - Expected to be newly observed on the October 6 flyby MESSENGER orbit insertion: March 2011 - Planned orbit around Mercury after flybys Mars Odyssey fuel remaining: almost 40 kilos - Hydrazine remaining on board Mars Odyssey annual fuel use: less than 1 kilo per year - Estimated propellant consumption Apollo 11 time on lunar surface: just under 22 hours - Matt Kaplan’s Apollo anniversary remark Apollo 11 returned lunar rock mass: about 22 kilograms - Sample mass brought back from the Moon Perseid meteor shower peak: August 12 - Best viewing around the shower’s annual peak Total solar eclipse date: August 1 - Bruce Betts’s skywatch segment Partial lunar eclipse date: August 16 - Visible from most continents except North America Largest recorded shuttle mission: 17 days, 15 hours, 53 minutes - STS-80, cited in trivia answer Shortest recorded shuttle mission: 2 days, 16 hours, 13 minutes, 12 seconds - STS-2, cited in trivia answer

Pivotal Quotes: "What in the world is water doing there? That's the question, all right." — Matt Kaplan: Introductory framing of the MESSENGER Mercury segment "The biggest surprise ... is that we saw ionized bits of pieces of water molecules, what are called water group molecules, that must have been derived from water at the surface of Mercury." — Sean Solomon: Explaining MESSENGER’s unexpected exospheric detection "The best evidence we have on Mercury that there are volcanic centers, and therefore there has been volcanic activity." — Sean Solomon: Summarizing the volcanic interpretation of Mercury’s plains

Implications: MESSENGER’s first flyby reshaped Mercury science by revealing possible water, active-looking geology, and stronger contraction evidence. Future flybys and orbit data should clarify Mercury’s polar volatiles, volcanic history, and internal evolution.