We can expect a totally different kind of trick-or-treater this coming Halloween. A rather large asteroid—discovered less than three weeks ago—is set to to fly past the Earth at a distance not seen in nearly a decade.

The asteroid, dubbed 2015 TB145, was discovered on October 10 by astronomers using the Pan-STARRS telescope. The object measures about 280 to 620 meters (920 to 2,034 feet) in diameter, so it’s pretty big—about the size of a skyscraper. Or two. Not only that, it’s moving at a velocity of 35 km/s (78,830 mph or 12,600 km/h), which NASA describes as “unusually high.”


Image credit: NASA

When 2015 TB145 makes its closest approach on October 31, it will zoom past the Earth at a scant 0.0032 AU, or 1.3 lunar distances. That’s about 479,000 km or 297,000 miles. This will be the closest object to flyby Earth of this size since 2006 when NEO 2004 XP14 flew past at 1.1 lunar distances. After the Halloween flyby, no object of this size will come as close again until August 2027 when NEO 1999 AN10 will approach within 1.0 lunar distance.

NASA says that 2015 TB145 will safely pass by the Earth and continue to following along its exceptionally eccentric and high-inclination orbit—which may explain why it wasn’t discovered until only a few weeks ago.

During the flyby, the asteroid will reach a magnitude luminosity of 10, so it should be observable to astronomers with telescopes. It’ll be seen best in the Northern Hemisphere, but the moon will be a relatively bright 80% waning gibbous at the time. Bad news for astronomers, but good news for the trick-or-treaters.


[ NASA and iTelescope via Gizmag]

Note: A correction was made to this article to clarify that no object of this size has appeared since 2006 and will not appear again until 2027. Other smaller objects have come closer since that time, but they were considerably smaller.


Email the author at george@gizmodo.com and follow him at @dvorsky. Top image by NASA/ESA/G. Bacon (STScI)

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