An estimate of the terrestrial influx of large meteoroids from infrasonic measurements

Abstract

[1] The influx rate of meteoroids hitting the Earth is most uncertain at sizes of $10 m. Here we make use of historical data of large bolides recorded infrasonically over a period of 13 years by the U.S. Air Force Technical Applications Center (AFTAC) to refine the terrestrial influx rate at these sizes. Several independent techniques were applied to these airwave data to calculate bolide kinetic energies. At low energies our flux results are within a factor of two in agreement with previous estimates. For 5-20-m diameter objects, however, our measurements of the cumulative number of Earth-impacting meteoroids are as much as an order of magnitude higher than estimates from telescopic surveys of near-Earth objects and satellite-detected bolides impacting the Earth. The precise cause of this disagreement is unclear, though we propose several possible explanations. From our infrasound study, our best estimate for the cumulative annual flux of impactors with energy equal to or greater than E (in kilotons of TNT equivalent) is N = 4.5 E À0.6 .

A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors

“…All events with estimated yields in excess of 1 kt are included. Figure 3 shows that this bolide flux at small sizes (less than 5 m in diameter) is in agreement within uncertainties with telescopic 8 data and earlier infrasonic 18 influx estimates. However, at larger diameters (15-30 m), both the bolide and infrasound 18 flux curves show an apparent impact rate at the Earth an order of magnitude larger than either that estimated by .…”

“…3) as a baseline for the 20-year period of the bolide survey, there is only a 13% chance that any random 20-year period would have an airburst as large or larger than Chelyabinsk. The independent 14-year survey by infrasound 18 (1960-74) detected a probable ,1.5-Mt airburst on 3 August 1963. Such a large event would be expected at the ,3% level during such a survey period.…”

“…Lunar crater counts converted to equivalent impactor flux and assuming a geometric albedo of 0.25 (grey solid line) are shown for comparison 9 , although we note that contamination by secondary craters and modern estimates of the near-Earthasteroid population that suggest lower albedos will tend to shift this curve to the right and downwards. Finally, we show the estimated influx from global airwave measurements conducted from 1960 to 1974, which detected larger (5-20 m) bolide impactors (red triangles) 18 using an improved method for energy estimation compared to earlier interpretations of the same data.…”

A meteor shockwave event recorded at seismic and infrasound stations in northern Taiwan

“…Taking a bulk density of 3 g/cm 3 and an initial velocity of 20 km/s for the meteor in question, this kinetic energy nominally means a pre-atmospheric mass of ~250 kg and a size of ~0.5 m across. Only moderate in (3) log 10 E 2 = 3.34 log 10 (P) − 2.58, E 2 ≤ 100 kT size compared to previously studied events (Brown et al 2002;Le Pichon et al 2013;Caudron et al 2016), such meteors impinge upon the Earth at the rate of a few tens every year (Silber et al 2009). We should note that our estimation of the pre-atmospheric source energy is rather crude and utterly contingent upon the uncertainty in the measurement of periods at the variable recording sites.…”

A catalog of video records of the 2013 Chelyabinsk superbolide

“…There was a possible 1.5 MT impact over the Indian Ocean in 1963 (Silber et al 2009), but data for that event are only from infrasound recordings and are not as robust as the measurable ground-damage for Tunguska or the extensive records of the Chelyabinsk airburst.…”