NASA NTRS · 20180000805
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Wheeler, Lorien. 2017-11-12. Asteroid Impact Risk Assessment. https://ntrs.nasa.gov/citations/20180000805
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Near-Earth Asteroids (NEAs) are minor bodies that vary in size from meteorite-sized objects to bodies that span tens of kilometers in diameter. One such object is the B-type asteroid (142) Polana, located in the Inner Main Belt (IMB). Polana is the progenitor of the New Polana family, which is postulated to be the origin of primitive NEAs like the B-type asteroid (101955) Bennu. To test this theory and further investigate the similarities in composition and aqueous alteration history between Polana and Bennu at the 3-μm band, we examined the spectra of Polana within the ~0.7.0-4.0-μm spectral range, utilizing the NASA Infrared Telescope Facility (IRTF) located in Hawai’i.
A test campaign was conducted placing meteorites in the 60 MW plasma Arcjet Interaction Heating Facility at NASA Ames Research Center, with the aim to achieve flight-relevant conditions for asteroid impacts in Earth's atmosphere and to provide insight into how meteoritic materials respond to extreme entry heating environments. The test conditions at heat flux of 4000 W/m2 and 140 kPa stagnation pressure are comparable to those experienced by a 30-meter diameter asteroid moving at 20 km/s velocity at 65 km altitude in the Earth's atmosphere. Test objects were a stony type H5 ordinary chondrite (Tamdakht) and an iron type IAB-MG meteorite (Campo Del Cielo), and included the terrestrial analogs Dense Flood Basalt and Fused Silica. All samples were exposed for only a few seconds in the plasma stream. Significant melt flow and vaporization was observed for both the stony and iron meteorites during exposure. Mass loss from spallation of fragments was also observed. Vapor emitted atomic lines from alkali metals and iron, but did not emit the expected MgO molecular band emissions. The meteoritic melts flowed more rapidly, indicating lower viscosity, than those of Fused Silica. The surface recession was mapped. The effective heat of ablation derived from this showed that ablation under these conditions occurred in the melt-dominated regime. Ablation parameters have an effect on ground damage estimates. A bias in ablation parameters towards the melt-dominated regime would imply that impacting asteroids survive to lower altitude, and therefore could possibly have airbursts with a larger ground damage footprint.