Tiangong-1 reentry location: We won't know exactly where out-of-control space station crash site will be until it falls, say experts

An out-of-control Chinese space station is plunging down to Earth. But we don't know exactly where or when.

We won't know either the location or time of the crash until just before it happens, experts have warned.

That is largely because we know very little about the satellite in general. The Chinese space agency, which runs the satellite, has not informed the world about the path of the satellite or what is contained in it.

Tiangong-1 is dropping quickly to Earth, and at some point over the weekend will fall into the atmosphere. Most of it is likely to burn up – but some of it could find its way to the ground.

It's unlikely that it will hit anyone. But experts have warned people not to touch anything they find – it may give off toxic fumes, or otherwise be dangerous – and to report it to the authorities.

Space agencies and experts are doing their best to track the satellite as it makes its way across the sky and towards Earth. It now estimates that it will drop down either on 31 March or 1 April.

But that estimate comes with a caveat. "At no time will a precise time/location prediction from ESA be possible," the space agency writes on its devoted page.

Even in the best case, just soon before the satellite drops, scientists will only be able to predict the crash site to an accuracy of about 1000 kilometres wide and a few thousand kilometres wide, Stijn Lemmens from ESA's space debris team told The Independent. Hard as it is to predict where the satellite will fall, it will be even more difficult to guess where the fragments it will break up into could be distributed.

Despite that uncertainty, experts are learning more about the satellite so they can say where it will not land, even if they cannot say where it will. Knowing roughly where the space station will drop "also means you can say with near certainty where it's not going to fall, and where you're not going to see anything," said Lemmens.

Just as it is very difficult to know where the satellite will land, it's also nearly impossible to know what might actually come down, whether anything will be visible, and whether any debris might actually make it to the ground without being burnt up.

"To be able to tell you what is coming down, I would need to know what's inside," said Lemmens, "which is information that only china's space agency has. So anything i would tell you could be a guess."

But just like it is possible to guess where the satellite won't land, it's possible to use previous drops to rule out what might and might not be able to make ti to the ground.

"If we invert the question a bit and ask what generally comes down from any type of spacecraft, it's fairly easy to guess," said Lemmens. "It's the materials that are either quite massive or heat resistant."

That might include objects built to withstand high temperatures and high pressure, such as propellant tanks, for instance. Or it could be things like docking adapters, which are big objects made out of heavy steel and so could last through their trip through the atmosphere.