Astrobiology target of opportunity: the Leonid storms.

HIGH METEOR RATES during recent Leonid storms offered a target of opportunity for studies of meteor ablation and the role of meteoric chemistry in supplying organic matter to the early Earth at the time of the origin of life (Chyba and Sagan, 1992, 1997). These studies fall under the Astrobiology Roadmap Goal No. 3, “Understand how life emerges from cosmic and planetary precursors” (Morrison and Schmidt, 1999; Des Marais et al., 2003). Given historical precedents dating from 1833 (called “a tempest of falling stars” by Agnes Clerke, a Victorian astronomy writer), the meteor storms were anticipated in the wake of comet 55P/Tempel-Tuttle’s return to Earth in early 1998. Repeated crossings of Earth with the comet’s dust trails provided rich meteor displays in the period November 1998–2002, enabling a great deal of previously unattainable studies and data. On these occasions, NASA collaborated with the U.S. Air Force in funding a series of airborne missions, called the Leonid Multi-Instrument Aircraft Campaigns, which brought a large group of researchers from seven nationalities to the best possible location on Earth and above the clouds and lower atmospheric water vapor for viewing the meteor storms. Four airborne missions were executed: to Okinawa, Japan, in November 1998 (Jenniskens and Butow, 1999); a flight from Tel Aviv, Israel to the Azores in 1999 (Jenniskens et al., 2000); a flight from Alabama to California over the continental United States in 2001 (Jenniskens and Russell, 2003); and a flight from Madrid, Spain, to Omaha, Nebraska, in 2002. In the final mission, the Spanish Centro de Astrobiologia, an affiliate member of the NASA Astrobiology Institute, acted as host. Except for the 2001 mission, all were two-aircraft campaigns for stereoscopic viewing of meteor trails and persistent trains. These airborne missions were supported by concerted ground-based campaigns worldwide, providing a wealth of new data on the composition and morphology of meteoroids, the physical conditions in meteors, and their influence on the Earth’s atmosphere. For the first time in these campaigns, modern instruments were deployed for meteor observations, which included optical video imagers and slit-less spectrographs, mid-infrared sensors, submillimeter spectrometers, and LIDAR (LIght Detection and Ranging). Results included the detection of the C-H stretch vibration band in the path of a bright Leonid fireball (Russell et al., 2000), suggesting that some organic matter may survive the ablation process intact. These and other results were published in a special issue of Meteoritics & Planetary Science (Vol. 34, 1999), in a special issue of Earth Moon and Planets (Vol. 8283, 2000, republished as the 600-page book Leonid Storm Research), in the Journal of Geophysical Research Letters (Vol. 27, 2000), in a 2002 special report (SP No. 15) of the Institute of Space and Astronautical Science of Japan, in a special issue of the Publications of the Astronomical Society of Japan (Vol. 55, 2003) , and in a special issue of the Advances of Space Research (2004, in press). Individual contributions were published in Astrophysical Journal, Monthly Notices of the Royal Astronomical Society, and other scientific journals. This special collection of papers in Astrobiology presents new results from two of the instruments