The now defunct Chinese space station Tiangong-1 is en route to crash into Earth – completing its “atmospheric reentry phase”. While experts have been aware that this would happen for more than a year, there has been huge uncertainty around the exact timing. As the station’s orbital altitude has decreased, however, this uncertainty has gradually reduced and it is now possible to determine that it will deorbit within a few days.
Most of the 8.5-tonne station will burn up and disintegrate as it passes through the atmosphere, though some debris may hit Earth. And although we have the capability to precisely control a spacecraft such as Rosetta – which orbited a few km away from comet 67P while being 405m km away from Earth and travelling at 55,000km per hour – we cannot actually predict the time and place of Tiangong-1’s potential impact on Earth, despite it being only 200km above us.
But why is it so difficult, and will science one day help us nail such predictions?