An asteroid designated 2015 TB145 will pass by the Earth at around 1.3 lunar distances on October 31 this year, traveling in excess of 126,000 km/h (78,293 mph). The asteroid was discovered less than two weeks ago using the Pan-STARRS array in Hawaii and is the largest object to so closely approach our planet in recent times.
Before you start panicking, NASA says that the object is expected to safely pass by the Earth and is following an eccentric and high-inclination orbit, which may help explain why it was not discovered until October 10 of this year.
Much closer than a "near miss" of 3.1 lunar distances by another recent asteroid, 2004 BL86, 2015 TB145 is of a similar size or greater than that object, but without an accompanying moon. Nevertheless, this now qualifies as the latest known close encounter, after 2004 XP14 in July 2006 at 1.1 lunar distances, and until the asteroid 1999 AN10 swings by Earth at less than one lunar distance sometime in August 2027.
Though possessing an absolute maximum magnitude of around 19.9, with which astronomers were originally able to determine its size to within a factor of 2, the relative magnitude when observed from the Earth at its closest approach is expected to be less than 10. As such, the asteroid won’t be visible with the naked eye, but should be observable using an amateur telescope of reasonable size and magnification.
Expected to travel through the well-known constellation of Orion across the evening of October 30 and the early hours of October 31, California time, residents of the United States should be able to observe the transit of this object in the night sky as it appears to move slowly through the star field.