You’ve probably already heard that a US spy satellite known as USA-193 is no longer able to keep itself up because the software on board has failed. This is a secret spy satellite so we don’t at present know what the software was (any guesses?). It is big enough to not totally burn up in the atmosphere, and there are concerns that the satellite has nasty toxins on board. But again, since it is a secret spy satellite we can’t know this either.
The expected date of entry is late February or early March.
Here is a source of info and a picture of the satellite.