Scientists have identified a second, mini-moon orbiting earth that has probably only been around for about 100 years. The small asteroid has a slightly tilted orbit, bouncing up and down through Earth’s orbital plane once a year. Over decades, as it scuttles along its path around the solar system, it twists back and forth. The asteroid has been declared a “quasi-satellite”, too distant to qualify as an actual satellite but cinched by gravity into a relatively close orbit around the sun.

The new discovery is among the smaller asteroids of the galaxy. Astronomers on Haleakala, Hawaii, estimate that it is larger than 120 ft (40m) but smaller than 300 ft (100m). Scientists with the University of Hawaii found the asteroid in April, using the Pan Starrs 1 survey telescope.

The new asteroid, known as 2016 HO3, is expected to remain in its tandem orbit with the Earth for centuries. Nor is it the Earth’s only fellow traveler: the asteroid 3753 Cruithne, named after ancient Celtic people also known as Picts, is another quasi-satellite.

Nasa scientists have hunted for years for asteroids that could strike the Earth, and estimate they have found more than 90% of those 1km wide or larger (noneappear a likely risk). Smaller objects can do considerable damage, however, as exemplified by the Chelyabinsk meteor explosion of 2013 and the Tunguska event of 1908, both over Russia.