It's pretty common for old satellites and other "space junk" to come falling back down to Earth. But while hundreds of pieces of debris come down each year, scientists are nervously watching a 19,000-pound Chinese space station's course because its out-of-control route is making it impossible to figure out where it will crash, CBS Denver reports.

The unmanned space lab named Tiangong-1 is expected to crash back down to Earth at some point in March.
China reportedly lost control of the lab nearly two years ago, in June of 2016. The Chinese government later released an estimate that predicted Tiangong-1 would come down at some point in late 2017.

The vague guess has led experts to conclude that the country's space agency has lost all ability to direct the crashing station's course or know where it will land.

According to a November analysis by the European Space Agency (ESA), the spacecraft's orbit "will inevitably decay sometime between January and March 2018, when it will make an uncontrolled reentry."
"Even a couple of days before it re-enters we probably won't know better than six or seven hours, plus or minus, when it's going to come down," Harvard astrophysicist Jonathan McDowell told The Guardian in 2016. "Not knowing when it's going to come down translates as not knowing where its going to come down."

We’re sure you’ve got plenty of good reasons to be worried in 2018. Now there’s one more worry to add to your teetering fear pile. A out-of-control Chinese satellite is about to smash into Earth and is expected to hit us within the next few months, with impact likely to take place at the beginning of March. As if that wasn’t scary enough, it’s now been claimed the Tiangong-1 space station is packed full of a toxic and corrosive chemical called hydrazine. This nasty stuff is used in rocket fuel and long-term exposure is believed to cause cancer in humans. It is being carried aboard the Tiangong-1, which is hurtling towards Earth and due to hit in March. Although most of the craft will burn up when it ploughs into the atmosphere, between 10 and 40 percent of its mass could survive and plunge to Earth. It will probably fall into the ocean and Britain is not believed to be in the firing line. In a statement, a spokesman from Aerospace, a space research non-profit based in California, wrote: ‘Potentially, there may be a highly toxic and corrosive substance called hydrazine on board the spacecraft that could survive re-entry. ‘For your safety, do not touch any debris you may find on the ground nor inhale vapors it may emit.’ Hydrazine is generally found as a colourless, oily liquid, although it can sometimes take the form of a white crystalline powder. Short exposure to can result in irritation of the eyes, nose, and throat as well as dizziness, headache, nausea, pulmonary edema, seizures and even coma, according to the United States Environmental Protection Agency. On September 14, 2016, China made an official statement predicting Tiangong-1 would reenter the atmosphere in the latter half of 2017. It’s now believed the collision will take place sometime in March 2018 and the out of control spacecraft could hit Spain, Italy, Turkey, India and parts of the US. Holger Krag, head of the European Space Agency’s Space Debris Office, said there was no telling where it could fall. She said: ‘The date, time and geographic footprint of the re-entry can only be predicted with large uncertainties. ‘Even shortly before re-entry, only a very large time and geographical window can be estimated.’ Although you probably don’t want to be standing anywhere near Tiangong-1 when it crashes to Earth, it may give you some comfort to know that falling man-made space debris has never killed a human here on Earth.

While much of the spacecraft would likely burn up in the atmosphere, ESA experts say portions could survive and reach Earth's surface.
According to reports, there is only a 1-in-10,000 chance that the massive space lab will actually crash into a populated area and damage buildings. While the odds are slim, scientists have only been able to narrow the crash zone down to between the 43° North and 43° South latitudes; an area that still includes parts of every inhabited continent on Earth.

"The date, time and geographic footprint of the reentry can only be predicted with large uncertainties. Even shortly before reentry, only a very large time and geographical window can be estimated," said Holger Krag, head of ESA's Space Debris Office.