Earth-viewing satellite perspectives on the Chelyabinsk meteor event Steven D. Millera,1, William C. Straka IIIb, A. Scott Bachmeierb, Timothy J. Schmitc, Philip T. Partaina, and Yoo-Jeong Noha aCooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO 80523; bCooperative Institute for Meteorological Satellite Studies, University of Wisconsin–Madison, Madison, WI 53706; and cAdvanced Satellite Products Branch, Center for Satellite Applications and Research, National Oceanic and Atmospheric Administration, Madison, WI 53715 Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved September 19, 2013 (received for review April 29, 2013) Large meteors (or superbolides [Ceplecha Z, et al. (1999) Meteor- event of June 30, 1908, when a stony meteoroid estimated to be oids 1998:37–54]), although rare in recorded history, give sobering of size ∼50 m left no hallmark crater but its shock wave caused testimony to civilization’s inherent vulnerability. A not-so-subtle widespread devastation over 2,200 km2 of Siberian forest (5). reminder came on the morning of February 15, 2013, when a large As it disintegrated in the atmosphere, the Chelyabinsk super- meteoroid hurtled into the Earth’s atmosphere, forming a super- bolide left a distinctive trail of dust, smoke, and ice debris. It can bolide near the city of Chelyabinsnk, Russia, ∼1,500 km east of be readily inferred from numerous surface-based photographs and Moscow, Russia [Ivanova MA, et al. (2013) Abstracts of the 76th videos of this trail that the object approached the region from the Annual Meeting of the Meteoritical Society, 5366]. The object ex- east at a highly oblique (low elevation) angle, and disintegrated in ploded in the stratosphere, and the ensuing shock wave blasted the the middle atmosphere. Using an array of georeferenced satellite city of Chelyabinsk, damaging structures and injuring hundreds. imagery, which readily observed the debris trail shortly after for- Details of trajectory are important for determining its specific mation, we attempted to quantify those notional observations and source, the likelihood of future events, and potential mitigation provide a top–down perspective on this rare event. measures. Earth-viewing environmental satellites can assist in these assessments. Here we examine satellite observations of the Chelya- Available Satellite Observations binsk superbolide debris trail, collected within minutes of its entry. Several Earth-viewing environmental satellites in both geosta- Estimates of trajectory are derived from differential views of the tionary and polar orbits (6) viewed the Chelyabinsk region within significantly parallax-displaced [e.g., Hasler AF (1981) Bull Am Me- minutes of the superbolide, capturing the debris trail left as it teor Soc 52:194–212] debris trail. The 282.7 ± 2.3° azimuth of trajec- passed through the middle atmosphere. The geostationary sys- tory, 18.5 ± 3.8° slope to the horizontal, and 17.7 ± 0.5 km/s velocity tems included several members of the European Organisation derived from these satellites agree well with parameters inferred for the Exploitation of Meteorological Satellites (EUMETSAT) from the wealth of surface-based photographs and amateur videos. constellation (Meteosat-7, -8, -9, and -10); the Chinese Meteo- More importantly, the results demonstrate the general ability of rological Administration Feng-Yun 2D; the Korean Meteoro- Earth-viewing satellites to provide valuable insight on trajectory re- logical Administration Communication, Ocean, Meteorological construction in the more likely scenario of sparse or nonexistent Satellite; and the Japanese Meteorological Administration Mul- surface observations. tifunctional Transport Satellite (MTSAT). These satellites, flying 35,786 km along the equatorial plane with orbital periods match- asteroids | atmospheric entry | remote sensing | multiangle | ing Earth’s rotation rate (geostationary orbits), effectively hover trajectory estimation Significance t ∼0320 UTC (∼9:20 AM, local time) on February 15, 2013, Aa large meteoroid entered Earth’s atmosphere, tearing Satellite observations of large meteors (superbolides) offer across the morning sky near Chelyabinsk, Russia (55.17°N, 61.40°E), important insight on trajectory through the atmosphere, and an industrial city located near the southern Ural Mountains, by extension, to orbital parameters that enable source attri- ∼1,500 km southeast of Moscow (1). The previously uncata- bution. On February 15, 2013, at 0920 local time, a superbolide logued meteoroid, with an estimated diameter of ∼15–20 m, exploded in the stratosphere near Chelyabinsk, Russia, issuing mass of ∼7,000–10,000 tons, and a velocity of ∼18 km/s, formed a large shock wave that damaged structures and injured hun- a superbolide (2) and exploded in the stratosphere with an esti- dreds below. The event was captured by Earth-viewing envi- mated total energy release of roughly 100–500 kilotons TNT (3). ronmental satellites that provided multiangle views of the Although we often think of Earth’s atmosphere as being a debris trail within minutes of formation. This paper documents tenuous media, an object entering it at speeds ranging from 12 to these observations and their use to derive trajectory details. 20 km/s (or 50–60 times that of a typical bullet) experiences Results compare favorably with surface-based camera/video a strong mechanical shock. For noniron meteoroids <100 m in estimates, demonstrating the unconventional utility of satel- size, the most common result is catastrophic fragmentation and lites to characterize events that are more likely to occur away production of an airburst explosion high above the surface, with from a dense surface network. the level of maximum energy deposition at lower altitudes for Author contributions: S.D.M. designed research; S.D.M. and W.C.S. performed research; more vertical trajectories and higher for more oblique ones (4). S.D.M., W.C.S., and A.S.B. contributed new reagents/analytic tools; S.D.M., W.C.S., A.S.B., Such was the case with the Chelyabinsk superbolide, whose high- T.J.S., P.T.P., and Y.-J.N. analyzed data; and S.D.M. wrote the paper. altitude explosion produced a powerful shock wave that blasted The authors declare no conflict of interest. the city below, damaging structures and injuring hundreds. Only This article is a PNAS Direct Submission. a scattering of fragments survived the entry and no impact crater Freely available online through the PNAS open access option. was found, although shortly after the event the Chelyabinsk re- Database deposition: Additional satellite information, including animations, can be gional police department discovered a ∼6 m wide circular hole in found at cimss.ssec.wisc.edu/goes/blog/archives/12356. an ice-covered lake near Chebarkul (54.96°N, 60.33°E), pre- 1To whom correspondence should be addressed. E-mail: [email protected]. sumably formed by one of the larger meteorites. In this regard This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. the Chelyabinsk events draws close parallels to the Tunguska 1073/pnas.1307965110/-/DCSupplemental. 18092–18097 | PNAS | November 5, 2013 | vol. 110 | no. 45 www.pnas.org/cgi/doi/10.1073/pnas.1307965110 Downloaded by guest on September 28, 2021 over a given location and provide 15–30-min imagery refresh rate. a signature that may be taken as consistent with the fireball However, the high-latitude (∼55°N) Chelyabinsk region resides observed from the surface. However, harkening back to the near the limb of their views, compromising the spatial resolution discussion about the nature of these scanning radiometer sen- quality of the imagery. sors, this hot-target interpretation is not correct. When expressed Complementing the geostationary observations was a seren- in terms of an equivalent blackbody (brightness) temperature, dipitously well-timed overpass from the polar-orbiting Defense the 3.9-μm measurement can appear warm if solar reflection is Meteorological Satellite Program (DMSP) constellation F-16 present. In this case, sunlight reflecting off small particles of the satellite and its Operational Linescan System (OLS) sensor, debris trail contributed to the received energy, producing ele- which provided a unique west/northwestern perspective on the vated 3.9-μm brightness temperatures (∼40 K warmer than the meteor trail. Considering the nature of the DMSP orbits (in- surrounding scene). This apparent warmth is thus a radiometric clined ∼98° to the equatorial plane, ∼830 km altitude, and ∼101- artifact that should not be misconstrued as sensible heat from min orbital period), which offer global coverage but poor refresh the plume. Fig. 1 compares 3.9- and 10.8-μm brightness temper- at any given location, the space/time proximity of F-16 to the atures from Meteosat-9, revealing much cooler temperatures for meteor’s entry (0324:40 UTC, or within 5 min) was as fortunate the trail at 10.8 μm (which contains no solar component, providing as it was useful to the meteor trajectory calculations. a better metric for assessing the thermodynamic temperature). Conventional environmental satellites use scanning radiom- Fig. 2 shows two distinct views of the meteor debris trail from eters to image the Earth scene. Unlike a camera, which ob- DMSP F-16 and Meteosat-9. Fig. 2, Inset, shows a surface-based serves its entire field of regard during a single exposure period, perspective (facing south) of the debris trail. Perhaps the most scanning radiometers sample only a small instantaneous geo- noteworthy structure along the trail is a convective “turret,” metric field of view (e.g., a 1–4-km area of surface) at a time. The corresponding roughly to the level of maximum energy de- sensor scans (e.g., in a raster or pendulumlike motion) one line position and approximate origination of the sonic blast wave felt at a time to construct the full coverage of the domain. The in Chelyabinsk. The western side of this turret, shaded from the sampling time interval defines the spatial resolution of each picture element (pixel) along the scan line.