A small handful of asteroids orbit entirely within earth's orbit. Now one has been found to orbit between Mercury and Venus. Its orbital period or "year" is only about 151 days, give or take a half day.

It is a rather large asteroid with an absolute magnitude of 16.3, which would make it more than a kilometer in diameter and likely more than a mile.

2020 AV2 was announced late yesterday (08 January 2020) by the Minor Planet Center. This is the bulletin they issued:

MPEC Link: 2020 AV2

Also the first article related to this find:

Link: First Intervenusian asteroid

Finally here is an orbit diagram from the JPL small body database browser, showing where it is today:

Click to view attachment