A Halloween Comet

A newly discovered space rock visible only with radar technology whizzed past Earth on Saturday.

Boo! (NAIC-Arecibo/NSF)

Give up, everyone. A large rock in space has the best Halloween costume this year.

NASA’s infrared telescopes captured the above image of the object called 2015 TB145 on Friday. It whizzed past Earth at around 1 p.m. EST on Saturday, but wasn’t visible to the naked eye. And because humans love finding Earth-bound things on the terrain of celestial bodies (see: Pluto’s heart), scientists determined that it looked like a skull:


When 2015 TB145 was first discovered earlier this month, scientists weren’t sure whether it was an asteroid or a comet. Asteroids are airless hunks of rock and metal too small to be called planets, originating from the asteroid belt between Mars and Jupiter. Comets are made of rock, ice, and frozen gases and orbit mostly in two areas—the Kuiper Belt, outside of Neptune’s orbit, and the Oort Cloud, at the very edge of the solar system—until the gravitational pull of a nearby planet knocks them out. Both are leftover material from the formation of the solar system 4.5 billion years ago.

On Friday, NASA said that scientists have determined the object is a comet, and—wait for it—that it’s dead. Like we said, best Halloween costume.

“We found that the object reflects about six percent of the light it receives from the sun,” said Vishnu Reddy, a research scientist at the Planetary Science Institute, in a NASA press release. "That is similar to fresh asphalt, and while here on Earth we think that is pretty dark, it is brighter than a typical comet which reflects only 3 to 5 percent of the light.” The object could be “cometary in origin,” he said, but it’s not acting like a comet anymore.

Every time they pass near the sun, comets lose chemical compounds called volatiles. Eventually, after several hundred orbits, those materials are depleted, and comets lose the gassy and dusty tails that are produced as they approach the sun’s heat. Without that signature trait, comets are considered dead, and they start looking a lot more like asteroids.

The dead comet is about 2,000 feet in diameter, and makes a complete rotation every five hours, according to NASA. At its closest approach, 2015 TB145 was 300,000 miles from Earth, which “astronomically is a pretty close passage,” Paul Chodas, manager of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory,” told CNBC Saturday. “Pretty close” is right: The moon is just 238,900 miles away.

The skull comet will return in September 2018, but at a much greater distance—about 24 million miles away from Earth.