A fireball that exploded over the Bering Sea in December 2018 was the second most powerful meteorite to visit Earth in more than 30 years.
The meteorite, which crashed through the news in March as a space rock that “eluded the world’s telescopes,” turns out to have been detected after all.
Originally spotted by military satellites, it took over 3 months for the event to be shared publicly through NASA’s website as reports of it moved through the correct channels during the holiday season and subsequent government shutdown.
At 173 kilotons, the fireball pulsed with more than 10 times the energy of the atomic bomb that fell on Hiroshima, though it was less than half as powerful as the meteorite that exploded over Chelyabinsk, Russia, in 2015. Because the Bering Sea object exploded over the sea rather than a city, it avoided inflicting the damage that the Chelyabinsk bolide did.
The Bering Sea bolide came in faster than its Russian counterpart and burst about 30 kilometers over the ocean, about the same height as at Chelyabinsk. Explosions with that sort of energy occur only about once every 25 years, said Peter Brown, a meteorite researcher at Canada’s Western University.
Had the Bering Sea fireball exploded in a clear sky, “it would have rivaled the noonday Sun.”
The Bering Sea meteorite may not have attracted much attention when it entered the atmosphere, but that’s not because it wasn’t immediately spotted. U.S. Air Force satellites saw it immediately, but it took time for them to pass the information on to NASA.
The location of the explosion, over the Bering Sea off the coast of Russia, likely helped to slow the report.
“I imagine in this case, because it took place in a sensitive part of the world, there might have been some extra confirmation,” said Kelly Fast, Near-Earth Object Observations program manager for NASA.
According to Lindley Johnson, NASA’s first planetary defense officer, several different systems combine to create the report that the Air Force relies on to observe incoming fireballs.
When pressed, Johnson, who served as an Air Force officer for 23 years working on national security space systems before his active duty retirement led him to a second career at NASA, said that he could not comment on the specific instruments that observed the event.
“Some of the data [are] provided by the nation’s most sensitive national defense and intelligence collection services, so as you can imagine we needed to make sure we got it done right,” Johnson said.
Air Force satellites weren’t the only mechanical observers of the powerful sky blast.
Brown found a record of the blast observed by the seismic and acoustic instruments maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The equipment relies on infrasound, the low-frequency shock waves created by explosions, to verify the ban on nuclear explosions for both military and civilian purposes. Similar shock waves are created by meteorite explosions.
Brown tweeted his observations on 8 March and said later that day that the observations appeared on the fireball and bolide data map maintained by the Center for Near Earth Object Studies.
#BeringSeaAirburst as detected infrasonically by #IS18 in Greenland. Long period signal near 03:50 UT of 20-25 sec consistent with ~200 kT energy. Longest period detected by atmospheric explosion in modern times other than #Chelyabinsk @westernu @IMOHQ @amsmeteors @ctbto_alerts pic.twitter.com/92FgSR5PO0
— Peter Brown (@pgbrown) March 8, 2019
According to Johnson, Brown’s work proceeded in parallel with NASA’s work with the Air Force, and the two groups communicated prior to the public release of information.
Right on Top of Us
Every year, millions of meteorites—most the size of a speck of dust—explode above Earth. Only a few of these “shooting stars” are spotted by people, as most detonate over the ocean. Even fewer crash into the ground before burning up in the atmosphere.
“You’re only going to see them when they’re right on top of you, but the atmosphere takes care of them anyway,” Fast said.
—Nola Taylor Redd ([email protected]; @NolaTRedd), Science Writer