Hi @gbenga

This is such an interesting topic. I believe it is not if but when something big hits us. However, the big one could be hundreds of thousands of years away. Of course, it could be tomorrow but probability makes it unlikely.

There are many PHAs that they know about and track but I know also they are sometimes surprised that they did not see one of the PHAs earlier.

You might like this site, spaceweather.com who track many cosmic data. Halfway down the page, they have a table of the current PHAs with one 18 m object that will pass as on Apr 15th at a distance of 0.9 LD. By LD they mean lunar distance which is the distance between us and the moon. So 0.9 means it will pass earth closer than the moon's orbit. This happens surprisingly regularly.

If a really big one hits then it would be disastrous and would be a huge impact on the world. We have a bigger and immediate crisis now to deal with but perhaps one day we can devise protection for our planet.