NASA's UARS satellite has fallen on Earth sometime Friday night, but the question of where still remails a mystery.

According to NASA's update on Saturday morning, the bus-sized Upper Atmosphere Research Satellite, or UARS, made its re-entry between 11:23 p.m. (EDT) Friday and 1:09 a.m. Saturday, penetrating the atmosphere somewhere over the Pacific Ocean.

Whether all the debris fell into the sea is uncertain, but it had been predicted that UARS would break into hundreds of pieces, with most of them burning up in the atmosphere, leaving around 26 pieces to hit the surface of the Earth, most likely as splashdowns. The heaviest among the pieces could weigh about 330 pounds.

The death plunge of UARS satellite has drawn a massive attention, due to the unpredictable nature of the event's when and where. North America was not ruled out from the satellite's landing zone, which was predicted to span 500 miles across the globe.

During the satellite's final hours the predicted re-entry time of late Friday was pushed later to early Saturday. It seems that the satellite just doesn't want to come down, Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics said.

While the probe was being tracked by radar stations and experts around the world, the tracking of the satellite remained difficult because of its shape, size and speed, according to Flight Lieutenant Mike Farrington, who had been monitoring the 35ft long satellite since its launch.

There are random forces of nature acting on the satellite that we can neither control nor predict, NASA spokeswoman Beth Dickey said Friday evening. Very small changes have very large consequences over time, and in this case, the change has been in the orientation of the spacecraft.

UARS marks the biggest Nasa spacecraft to fall on Earth, uncontrolled, since the post-Apollo 75-tonne Skylab space station and the more than 10-tonne Pegasus 2 satellite, both in 1979, according to Guardian.

Since the beginning of the Space Age, no injury has been recorded resulting from re-entering space objects, NASA assured the public on its website. The chances for someone to be hit by the NASA satellite were said to be one in 3,200, while any particular person's odds were one in 21 trillion.

The video below shows UARS in its final spins around the planet, a stunning view captured by an amateur astronomer Thierry Legault from Paris.
The satellite appears to be tumbling, perhaps because a collision with satellite debris a few years ago, Legault told
The variations in brightness are rapid and easily visible to the human eye.

UARS was a $750 million mission deployed from the shuttle Discovery in 1991 to study the Earth's atmosphere and its interactions with the sun. It measure important ozone depletion related to climate change. According to NASA reading from UARS gave evidence that Chorine in the atmosphere is at the root of the polar ozone hole.