For the first time ever, a meteor has grazed in and out of Earth's atmosphere, slowing enough to become a temporary satellite that perhaps lasted a full orbit.
By evening on September 21st, an earlier storm had moved eastward and left skies over the British Isles beautifully clear.
Martin Goff, an officer with the Greater Manchester [England] Police, was making his rounds when he spotted a dazzling meteor at 22:55 p.m. (21:55 Universal Time). "I immediately pulled the van over to better see the fireball," he recounts. "Although not an experienced astronomical observer I was able to log relevant information such as altitude and azimuth relative to the straight road I was on and to trees and streetlights nearby." He estimates it was about as bright as a full moon and remained visible for 35 to 40 seconds, fragmenting for at least the last half of that. "I was just flabbergasted to have seen it!"He was hardly alone in his amazement. Friday-night crowds were out and about when the bolide appeared, delighting and amazing untold thousands as it broke into dozens of pieces as it glided east to west across the sky. Dirk Ross, who tracks bright meteors and meteorite finds worldwide, logged 564 eyewitness reports from England, Scotland, Ireland, France, Belgium, The Netherlands, and Norway.
A few hours later, Ross received another burst of 126 sightings. But these weren't from Europe — instead, a fireball had appeared over southeastern Canada and the U.S. Northeast. What at first seemed the unlikely arrival of two dramatic bolides in a single night might turn out to be something much more historic and scientifically profound.
Mathematician Esko Lyytinen, a member of the Finnish Fireball Working Group of the Ursa Astronomical Association, has analyzed the European sightings and concludes that the two events resulted from a single large body grazed the upper atmosphere, dipping to an altitude of 33 miles (53 km) over Ireland before escaping back to space. Because it arrived moving at only about 8 miles (13 km) per second, barely above Earth's escape velocity, it lingered for more than a minute as it crossed the sky. (This explains why some witnesses mistook it for reentering spacecraft debris.)Lyytinen says the brief atmospheric passage took its toll. As the meteoroid broke apart, its velocity dropped to just 5.7 miles (9.2 km) per second, too slow to make an escape back to space. Instead, it became a temporary satellite of Earth, looping completely around the globe before reentering the atmosphere — this time for good.
A second analysis of photos and videos of the European event, by aerospace engineer and meteor expert Robert Matson, likewise suggests that a big chunk of this Earth-grazer ended up in a temporary orbit with an inclination of about 54° (corresponding to the latitude of its "perigee" over Ireland). Its single looping orbit was highest, about 3,930 miles (6,330 km), somewhere south of Australia, before it boomeranged back to a fiery finale.
However, after a close look at the event over North America, Matson is now skeptical that it's related to the earlier graze seen across the Atlantic. "Using two all-sky videos from Ontario, Canada, I was able to roughly triangulate the location of the Québec fireball to a spot between Ottawa and Montréal," he says. "Unfortunately, I cannot dynamically link this location and timing with that of the U.K. fireball — it is too far west." Moreover, Matson adds, the videos show a fairly short-duration event and a much steeper trajectory than a UK remnant could have had.
A subsequent analysis by John Mason and Nick James of the British Astronomical Association likewise argues against the two fireball events being related. They calculate that the brightest fragments seen over the U.K. exited the atmosphere with velocities of 5.3 and 4.9 miles (8.5 and 7.8 km) per second, too slow to send them looping around Earth.
There've been widely seen grazers before, though nothing quite like this. On the evening of October 9, 1992 (also a Friday, by the way), thousands witnessed a bolide that broke apart as it screamed up the East Coast. A piece of it struck a parked car in Peekskill, New York. An even larger meteoroid streaked across the Rocky Mountain sky in broad daylight on August 10, 1972, coming as close as 35 miles (57 km) before returning to interplanetary space. (Its velocity was too fast to become captured.)
If the fireballs seen in North America and Europe are not part of the same event, then they were a remarkable near-coincidence. Lyytinen explains that getting a final determination will require close attention to several subtle factors: the object's angle as it exited the atmosphere over the Irish coast, how rapidly the fragments were moving apart from one another, and how the Coriolis effect (due to Earth's rotation) affected the trajectory. Large fragments of the original meteoroid could have reentered the atmosphere anywhere along the orbital track.
In any case, high-quality snapshots and videos from astonished onlookers have been key to piecing together the story of September 21st's double feature. For example, Ross has collected 31 videos of the meteoroid passing over Europe.
Photographer Damien Stenson was definitely in the right place at the right time with the right equipment, as he was taking long exposures of the stars and scenery along the Cliffs of Moher on Ireland's west coast. Two of his images are especially diagnostic — and beautiful — in that they clearly show the fragmenting object framed by the Big Dipper and other far-northern stars.
"I spend a lot of time out photographing the Milky Way, meteors, etc.," Stenson comments, "but this was the most impressive sight I've seen yet."