A brilliant
fireball in the Virginia sky on Sunday was likely a natural meteor event and
not the remnants of a Russian rocket, scientists now say, a reversal from
yesterday's initial analysis.
On Monday,
Geoff Chester of the U.S. Naval Observatory told SPACE.com that the loud
boom and flash of light seen in the skies over Norfolk and Virginia Beach was
likely the second
stage of the Soyuz rocket that launched Expedition 19 to the International
Space Station last Thursday.
However, U.S.
Strategic Command has since reported that the rocket re-entered Earth's
atmosphere near Taiwan, on the other side of the world, several hours after the
reports of the
fireball. So both its timing and entry location rule out the rocket as the
explanation for the fireball.
"Well,
we're all entitled to a 'mulligan' now and then, right," Chester wrote SPACE.com
in an email, adding that he deferred Strategic Command. (A mulligan is a do-over
in golf.)
"However,
it is still a remarkable coincidence that a random rock would fall out of the
sky along a path that is very similar to the ground-track of a decaying rocket
body," Chester added. "But this is what makes science fun!"
The
evidence now suggests, he said, that the loud boom and streak of light was
created by a natural meteor, or bolide, burning up as it plummeted through
Earth's atmosphere.
"I'm
confident that this was a meteoric event," Bill Cooke of NASA's Marshall Space Flight Center in Alabama said this morning.
Sunday
night light show
Residents
of the areas around Norfolk and Virginia Beach, Va., began calling 911 Sunday
night with reports of hearing a loud boom and seeing a streak of light that lit
up the sky, according to news reports. Some said their houses shook.
The
difficulty in distinguishing the cause of such a fireball lies in getting
accurate reports with the right kinds of information.
"Most
of the eyewitness accounts don't mention altitudes and azimuths. They just
describe the light show," Chester explained.
Chester said he received "credible
reports" from amateur astronomers that, when combined with the area from
which reports of the fireball originated, "fit the ground-track of the rocket
body with remarkable similarity."
"The
only problem is that the time the rocket was predicted to pass over the area
differs by some 10 minutes from the reported times that the fireball was
seen," Chester said. The difference could be the result of an error in his
prediction software or could be 'real,'" he said.
But,
"based on the evidence I have at hand now, I have to lean more toward the
'natural' explanation," Chester said.
Space rocks
the size of small cars plunge into Earth's atmosphere several times a year,
typically burning up before reaching the ground. Most go unreported since they
fall over uninhabited areas (our planet's surface is two-thirds ocean).
Investigation
continues
Cooke
agreed that tracing the fireball's source is tricky given the paucity of
information available.
"It's
very hard to do given only eyewitness accounts," Cooke said in a telephone
interview. He plans to look at sound measurements (meteors make sounds below
human hearing as they travel through the atmosphere) taken that could reveal
the energy of the bolide and in turn give a rough estimate of its size.
Video of
the object, if any surfaces, could also shed light on the trajectory of the
fireball. Such video often comes from the dashboard cameras in police cars,
Cooke said. "They're out that time of night, and the camera is always
running."
But, he
said, "It's going to be very hard to get more information" on the
nature of the bolide.
Whether or
not any fragments of the meteor might have made it to Earth's surface is
uncertain. "Most bolides do not," Cooke said. "The atmosphere is
very good at protecting us from falling rocks."
A few space
rocks do occasionally make it to the surface though. In recent years, pieces of
a bolide were found after a meteor event in western Canada, Chicago and Peekskill, NY, Cooke said. Fragments of a meteor that originated from an asteroid that blew
up over the skies of Africa last October were also recovered in the
Sudanese desert.
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