A mysterious fireball that blazed through the skies over Australia wasn't an asteroid as some had thought, but rather something more mundane, scientists say; a piece of Russian space junk.

Calls reporting the fireball to authorities flooded in from the Australian states of New South Wales, Victoria and Tasmania.

"We received numerous emergency calls from people concerned," Country Fire Authority spokeswoman Andrea Brown said. "People believed they had witnessed an aircraft crashing into the sea."

But the fireball on Thursday was in fact part of the final stage of a Russian Soyuz launch vehicle that had blasted off July 8 from Kazakhstan, experts said.

The rocket stage piece, the size of a small truck, is designed to drop back toward the Earth and burn up, they said.

"What you're seeing in that fireball is it slowing down really fast," astronomer Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics said. "It's belly-flopping on the world's atmosphere at 18,000 miles an hour. That really hurts."

Such sights are "not usually seen because most of the Earth is either ocean -- or very sparsely inhabited," he said. "And of course, if it comes down in the daytime, you may not notice as easily."

Astronomers had been expecting some sort of cosmic light show courtesy of the Soyuz launch that put a weather satellite into orbit, and said the reentry hit its projected path exactly where intended.

"Apparently, the tracking and impact prediction matched, [in both] time and location, what we saw," Sydney Observatory astronomer Melissa Hulbert said.

Australians not armed with that foreknowledge took to Twitter and posted videos to YouTube in hopes of getting an explanation for the dramatic fireball that crossed the skies from southwest to northeast about 9:42 p.m. local time.

The segment of Soyuz space junk was likely around 5 feet long by 11 feet wide, Hulbert said.

The world is surrounded by a veritable halo of space debris; NASA scientists have said they estimate at least 20,000 objects larger that a softball are in in cloud of debris circling our planet, and smaller pieces almost certainly number in the millions.

At orbital velocities of more than 28,000 miles per hour, even small objects could do great damage to satellites or other spacecraft in orbit in the event of a collision, experts say.