Here Comes Spooky!

Nothing this large has come so close to Earth (as far as we know) since 2006. That’s when near-Earth asteroid 2004 XP14 passed 268,700 miles (432,400 kilometers) from Earth. Its size was estimated to have a lower limit of 850 feet (260 meters). However, a newly-discovered object, 2015 TB145, measuring at least 900 feet (280 meters) in diameter will pass 302,000 miles (487,000 kilometers) from our planet during the predawn hours of October 31. On a cosmic scale, that’s only a black cat’s whisker away, but still 1.3 times the distance to the Moon, posing absolutely no risk of a collision with Earth. So despite the nickname given to it (“Spooky”), this object is nothing to be afraid of. Nevertheless, its encounter with Earth will be close enough that astronomers using radio telescopes can attempt to capture radar-glimpses of its surface, employing new techniques that may resolve details to perhaps only seven feet (two meters) across.

Discovered on October 10 by the Panoramic Survey Telescope & Rapid Response System (PAN-STARRS) in Hawaii, 2015 TB145 has a highly-inclined orbit tilted nearly 40 degrees from the plane of the Solar System. Most asteroids typically circle the Sun with a low inclination—more or less along the plane—having formed from the same proto-stellar disk as our star and the other planets. Spooky’s high inclination has some astronomers suspecting that our Halloween visitor is actually a comet, many of which also have steeply-tilted orbits, so they’re very eager to get a good look at it.

Even when closest to Earth, Spooky is expected to be far too faint to be seen with the unaided eye, with an estimated apparent magnitude of ten on the astronomical scale of brightness. For comparison, more than 300,000 stars in the sky are brighter than this, and the naked eye can perceive only about 6,000 of those under ideal conditions. The light of a waning gibbous moon will be of no help, either, but experienced observers with medium-size telescopes may be able to catch it between midnight late Friday and sunrise on Saturday morning as it moves from between the constellations Orion the Hunter and Taurus the Bull to a region between Gemini the Twins and Auriga the Charioteer before being washed from view in the predawn twilight. At about 3:30 a.m. PDT, astrophotographers may have a chance to snap Spooky as it passes within a degree of the famous supernova remnant M-1, also known as the Crab Nebula.

For those interested in seeing Spooky zip by, live webcasts of the flyby will be aired online by the Virtual Telescope Project (Friday, October 30, at 5:00 p.m. PDT) and Slooh.com (Saturday, October 31, at 9:30 a.m. PDT), both with live commentary. But don’t expect to see much more than a tiny dot moving very slowly against the stars—remember, it’s more than a quarter of a million miles away! Close enough to be spooky, not scary.