From a spreadsheet I developed during the Ceres mission, I've calculated that the Hubble Space Telescope would barely be able to see it, with a resolution of only 0.026 pixels.This small asteroid is Earth's constant cosmic companion [JPL]
June 15, 2016
A small asteroid has been discovered in an orbit around the sun that keeps it as a constant companion of Earth, and it will remain so for centuries to come.
As it orbits the sun, this new asteroid, designated 2016 HO3, appears to circle around Earth as well. It is too distant to be considered a true satellite of our planet, but it is the best and most stable example to date of a near-Earth companion, or "quasi-satellite."
2016 HO3 was first spotted on April 27, 2016
It has a diameter of between 40 and 100 meters.
Maximum distance from Earth: 39 million km (100 times the distance to the moon)
Minimum distance from Earth: 14 million km (38 times the distance to the moon)
I used the minimum distance, and a diameter of 70 meters, for my Hubble resolution calculation.