Skull-Shaped Halloween Asteroid Zips by Earth, a Treat for Scientists

On Halloween night, while ghouls and goblins did their trick-or-treating, an asteroid that is most likely a dead comet made a close flyby of Earth, with radar images revealing its eerie skull shape.

On Saturday (Oct. 31), the asteroid 2015 TB145 passed by Earth at a range of just over 300,000 miles (480,000 kilometers), placing it just outside the orbit of the moon, where it posed no threat to the planet. The timing of the flyby earned the asteroid - which is about 2,000 feet (600 meters) across - the nickname "Spooky" and "Great Pumpkin."

Unfortunately for skywatching hobbyists, 2015 TB145 was extremely difficult to see from the ground, but the online Slooh Community Observatory hosted a webcast Saturday afternoon that featured updates on the asteroid's path, and discussions about the dangers of near-Earth asteroids. [Related: Boo! Halloween Asteroid Looks Just Like a Skull]

NASA observed the asteroid with radar in infrared using its NASA Infrared Telescope Facility (IRTF) in Mauna Kea, Hawaii.

"The IRTF data may indicate that the object might be a dead comet, but in the Arecibo images it appears to have donned a skull costume for its Halloween flyby," Kelly Fast, IRTF program scientist and acting program manager for NASA's NEO Observations Program, said in a NASA statement Friday (Oct. 30).

Slooh used a remotely operated observatory in the Canary Islands to record animations of asteroid 2015 TB145 passing by. The "dead comet" asteroid looks like a bright object speeding across a starry background in those views. It was Slooh who nicknamed the asteroid "Spooky," and the online observatory was thrilled to see the space rock's skull shape in radar views.

"We all saw those dramatic images of the skull-like object whirling through space captured by NASA's Arecibo Observatory," Slooh's Tricia Ennis wrote in an email update. "We got a kick out of how appropriate our 'Spooky' moniker ended up being, here at Slooh."

The flyby was a treat for scientists, because it allowed them to see the space rock up close, with a radar resolution of as little as 6.6 feet (2 meters) on the surface. On Saturday, scientists fired radio waves at the passing space rock using a 110-foot-wide (34 m) antenna at NASA's Deep Space Network facility in Goldstone, California. The radio waves that bounced off the asteroid and came back to Earth were then collected using the Green Bank Telescope in West Virginia and Puerto Rico's Arecibo Observatory.

This first series of radar images of the Halloween asteroid 2015 TB145 show that it is about 2,000 feet (600 meters) wide and roughly spherical in shape. The images were taken by the Arecibo Observatory in Puerto Rico.

Credit: NAIC-Arecibo/NSF

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This radar image of asteroid 2015 TB145, which NASA says is likely a dead comet, was captured using the Arecibo Observatory in Puerto Rico on Oct. 30, 2015 with a resolution of 25 feet per pixel. The skull shaped asteroid flew by Earth on Halloween (Oct. 31). Credit: NAIC-Arecibo/NSF

by Calla Cofield

Skull-Shaped Halloween Asteroid Zips by Earth, a Treat for Scientists