An asteroid about the size of a truck has zoomed past the Earth at an alarming close trajectory taking it six times closer than the moon. The object ranged between 15 and 32.8 feet in length, and it’s the closest an asteroid has flown past Earth since last September.

It’s hard for scientists to spot these asteroids, particularly ones that are as small as these. Scientists at the University of Arizona discovered the asteroid, 2017 BH30, on Sunday hours before it passed by Earth from a distance of just 40,000 miles away, similar to the distance of some satellites in geosynchronous orbit that are used for weather monitoring and forecasting.

It’s the third time an asteroid has flown past Earth within the orbit of our moon this year. It happened earlier this month with asteroid 2017 AG13 at half the distance between the Earth and the moon, and that asteroid may have been up to 111 feet wide.

“Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth’s neighborhood,” NASA says on its website. “Composed mostly of water ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter. The scientific interest in comets and asteroids is due largely to their status as the relatively unchanged remnant debris from the solar system formation process some 4.6 billion years ago. The giant outer planets (Jupiter, Saturn, Uranus, and Neptune) formed from an agglomeration of billions of comets and the left over bits and pieces from this formation process are the comets we see today. Likewise, today’s asteroids are the bits and pieces left over from the initial agglomeration of the inner planets that include Mercury, Venus, Earth, and Mars.”