The European Space Agency's GOCE research satellite was launched in 2009 to chart the Earth's gravitational field. But it ran out of fuel.
Scientists say the 1,100-kilogram (2,425-pound) satellite already has fallen to an altitude of 170 kilometers (105 miles) and will steadily spiral back to Earth over the next few days.
"When they run out of fuel and they can no longer give themselves periodic kicks to stay in orbit, they begin to slowly drop," said Seth Shostak, Ph.D.
Shostak is a senior astronomer at the SETI Institute in Mountain View. He and his colleagues research life in the universe. Shostak says the GOCE satellite will continue to drop until it plunges into the Earth's atmosphere.
Pieces of the satellite will begin to burn up and essentially become asteroids. But a couple hundred pounds of it land here back on Earth.
Shostak stay it isn't likely anyone will be struck by a piece of the satellite.
"Most of the earth is covered by water," Tom Norton said. "So the chances are it's going to land in the ocean, I assume."
Norton was one of many Bay Area residents visiting the Foothill Observatory in Los Altos Hills on Friday night. His assumption is spot on, according to Shostak.
"The chances are that nobody is going to see it," Shostak said. "t's going to land in the ocean and nobody will notice except a few fish."
The European Space Agency said Friday that humans are 250,000 times more likely to win the lottery than to get hit by the debris weighing up to 90 kilograms (200 pounds) that may survive the breakup.
They add that the satellite should re-enter the atmosphere Sunday or early Monday.
(The Associated Press contributed to this report)