You may have heard about the asteroid that will pass close to Earth this weekend. At 1:05 p.m. EDT on Saturday, Oct. 31, asteroid 2015 TB145 will pass within 300,000 miles, or about 1.3 lunar distances, of Earth.

It will pass within about 178,000 miles of the moon as well. There is no threat of impact to either Earth or the Moon.

"The trajectory of 2015 TB145 is well understood," said Paul Chodas, manager of the Center for Near Earth Object Studies at NASA's Jet Propulsion Laboratory, Pasadena, California.

This visitor dubbed the “Halloween Asteroid” was discovered on Oct. 10 by the 1.8-meter telescope at the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). Pan-STARRS surveys about 80 percent the skies above Haleakalā, a dormant volcano on Maui, Hawaii, looking for movement which could indicate a previously unknown Near-Earth Object (NEO).

So why didn’t we see this earlier?

While the telescope does an excellent job of finding asteroids and comets, discovering 32 so far this year and setting a record of 19 in one night in 2011, finding NEOs can be as much a matter of luck as technology. An asteroid this small, about 1,300 feet wide, is particularly difficult.

“You may spot something one night but weather may prevent the additional observations necessary to determine its orbit.” explained Dr. Ken Chambers, Pan-STARRS Director. “Also, a fully illuminated [by the sun] object is much easier to see than a partially illuminated one. Think crescent moon versus full moon. These objects are rarely fully illuminated, finding them can take a while.”

The asteroid’s odd orbit delayed its discovery as well. The planets and most asteroids are distributed along the ecliptic plane, a flat disk shape extending out from the Sun. 2015 TB145 orbits at a 40-degree angle to that plane, where Pan-STARRS and previous sky surveys have spent less time studying.

Pan-STARRS provides more increasing our knowledge of Near Earth Objects. Part of the process required to spot differences between observations is cataloging and tracking each object the camera spots. This provides very valuable data about our stellar neighborhood and beyond.

“We are taking a census of solar system, of the Milky way and ultimately the universe.” added Chambers.

The Institute for Astronomy and University of Hawaii plan a large public release of data and images gathered by Pan-STARRS in 2016.

Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.