Officials continue to investigate the cause of the loud “boom” that surprised many Hoosiers throughout south central Indiana earlier this week.
Residents in Monroe and surrounding counties reported hearing what sounded like an explosion early afternoon Wednesday. Some said the sound shook their houses.
The Monroe County Sheriff's Office had not identified a source within the county as of Thursday morning.
The National Weather Service Indianapolis branch noted lightning and high winds in the Johnson County area Wednesday, but meteorologist Aaron Updike said nothing was out of the ordinary.
One possible cause could be a fireball passing overhead, according to Robert Lunsford, contributing editor and fireball report manager for the American Meteor Society. Fireballs are extraordinarily bright meteors whose sighting is often followed by a loud boom.
The AMS received two reports late Wednesday of a fireball passing low — about 700 to 800 feet — over Columbus and Bloomington, around 12:20 p.m.
The organization received two more reports Thursday morning of a fireball in northern Kentucky, south of Cincinnati, around 12:45 p.m. Wednesday. Lunsford said the information in the reports leads him to believe they’re describing the same event, and his preliminary explanation is that a meteor caused the boom people heard.
“[What] may account [for] why we have a low number of reports [is] the fact that it was obscured by clouds,” Lunsford said.
The Bloomington report described the event as a bright white flash: “I’ve heard reports of the sound but no one mentions that flash just before it.”
The IU Department of Astronomy was inundated with calls Wednesday about the boom. Postdoctoral researcher Vaclav Pavlik said, given the known information, it’s plausible the sound was caused by a fireball or meteor. He said it likely won’t be possible to confirm, though, unless somebody actually finds it.
“From what I’ve seen on the map that (AMS) provides, they have a trajectory that would go from Morgantown to Greenwood,” Pavlik said.
He attributes the large lag in time from the Indiana reports of seeing a fireball (12:20 p.m.) to those who heard the boom (around 12:44 p.m.) to people possibly misremembering when they saw or heard it, since the reports were filed hours after the event. But he said it makes sense, considering that light travels faster than sound.
The Indiana Department of Homeland Security said it was aware of the sound but had not been asked to assist and had no information on the boom.
Rumors swirled online that the sound might have come from an ammunition storage exploding at Camp Atterbury, the National Guard base near Edinburgh. Residents of Johnson and Brown counties reported being shaken by the boom.
Master Sgt. Jeff Lowry, spokesperson for the Indiana National Guard, said there was “no explosive or live fire training” scheduled at Camp Atterbury on Wednesday.
When asked directly if the sound came from the Camp, Maj. Jesse Bien, the camp's public information officer, said the camp was not responsible for the sound.
Mark Dobbs, community planning liaison with Naval Support Activity Crane in Martin County, said the base conducted demolition operations Wednesday morning and afternoon, and that the afternoon operations took place between 1 and 1:30 p.m. Dobbs could not comment on what the operations were or if it was what people reported hearing.