Astounding Comet Hartley 2

Episode Summary

Executive Summary: This Planetary Radio episode spotlights Deep Impact/EPOXI's flyby of comet Hartley 2, where Jessica Sunshine explains unexpected ice and CO2 jets from different comet regions, suggesting a far more complex nucleus than a simple dirty snowball. The show also covers Hayabusa’s asteroid sample return, NASA’s NanoSail-D as a precursor to LightSail, space-themed children’s books, and Bruce Betts’ sky update and listener contest.

Main Topics: Deep Impact/EPOXI’s Hartley 2 flyby: Matt Kaplan interviews Jessica Sunshine about the mission’s surprising comet images, especially jets, ice particles, and the comet’s unusual region-by-region behavior. Unexpected comet composition and activity: Sunshine explains that Hartley 2’s ends are rich in CO2 and ice crystals while the middle appears dust-covered, CO2-poor, and water-rich, challenging simple comet models. Hayabusa sample-return milestone: Emily Lockdawala reports that Japan’s Hayabusa mission recovered at least 1,500 likely asteroid particles from Itokawa, a historic surface sample return beyond the Moon. NanoSail-D and the future of solar sails: Bill Nye describes NASA’s NanoSail-D launch as a small sail designed to deorbit via drag, and as technology relevant to the Planetary Society’s LightSail 1. Space books for young readers: Emily recommends children’s books including Almost Astronauts and Team Moon, emphasizing their appeal to both kids and adults and their historical perspective on space exploration. Night sky, space history, and listener participation: Bruce Betts gives the sky report, recalls Mariner 4 and Mars 2 history, shares a listener-composed 'What's Up' ditty, and runs a Discovery shuttle trivia contest.

Key Arguments: Hartley 2 produced the most dramatic close-up comet images yet, revealing active jets and visible particles around the nucleus. The comet’s ends and middle behave differently, implying either compositional diversity, evolutionary change, or dust insulation effects. Comets are not simple uniform snowballs; exploration keeps revealing greater diversity and complexity than existing models predict. The Hayabusa mission represents a landmark because it returned the first surface samples from beyond the Moon. NanoSail-D could demonstrate a low-fuel way to remove spacecraft from orbit and help mitigate space debris while validating sail-deployment technology for LightSail. Manual image deconvolution and careful interpretation were essential to extracting science from the blurred Deep Impact/EPOXI data.

Data Points: Flyby distance: 700 kilometers (435 miles) - Jessica Sunshine says Deep Impact was far enough from Hartley 2 that fluffy particles likely caused no damage. Ice/dust particle speed: under 1 meter per second - Sunshine describes the comet’s particles as moving slowly and being very fluffy. Number of images collected: 120,000 - Sunshine notes the mission collected a very large image set during the encounter. Asteroid particles recovered: at least 1,500 - Hayabusa’s sample chamber analysis reportedly found likely asteroid dust from Itokawa. NASA launch date reference: last Friday / November 2010 era - Bill Nye refers to the launch of NanoSail-D shortly before the episode aired. Orbit altitude: 400 kilometers above Earth - Bill Nye explains NanoSail-D’s drag-based deorbit concept. Space Shuttle Discovery flights: 39 flights - Bruce Betts discusses Discovery’s planned final mission and its record as the most-flown orbiter. Earth orbits by Discovery: 5,628 times - Bruce Betts gives a usage statistic for Discovery’s operational life. Dockings with ISS: 11 - Bruce Betts mentions Discovery docked 11 times with the International Space Station. Deep Impact encounter gap: 5 years and 4 months - The episode contrasts the 2005 Tempel 1 impact with the 2010 Hartley 2 flyby.

Pivotal Quotes: "These are pictures you really have to see." — Matt Kaplan: Introductory tease for the Deep Impact/Hartley 2 segment. "It's a testament to the spacecraft or to the fluffiness of this stuff that apparently didn't do any damage." — Matt Kaplan: Discussing why particle impacts did not harm Deep Impact during the comet flyby. "Comets not just being simple snowballs or dirty ice balls... we have evidence of that." — Jessica Sunshine: Her explanation of why Hartley 2 complicates standard comet-formation theories.

Implications: Listeners get a vivid update on a mission that is reshaping comet science, while the episode also highlights practical spaceflight advances, historic sample-return achievements, and educational outreach that broadens public engagement with exploration.