UPDATE! You can read the Facebook Libra whitepapers here:
We are excited to announce that the website of the Facebook cryptocurrency wallet is online. Libra is built on a secure, scalable, and reliable blockchain and is designed to help bring people everywhere equal access to financial services and is backed by a reserve of assets so that its value stays stable. Libra is reinventing money so it can be used in countries around the world. It can easily be sent to anyone and exchanged into local currencies.