It's undead! (NAIC-Arecibo/NSF)

In case you haven't heard, there's a fairly large, fairly unexpected space object coming fairly close to Earth today. Now scientists say it's probably a comet — a dead one. Have you ever heard of anything so Halloween appropriate?

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When object 2015 TB145 was spotted a couple of weeks ago, it seemed like it was probably an asteroid. Asteroids are made of rock and metal, and while they vary widely in size, shape and composition, you shouldn't expect to see any of them from Earth without at least a small telescope. If a comet the size of 2015 TB145 came so close to Earth, we'd expect quite a show: Comets are made of ice and dust, and when a close pass of the sun heats them up, that ice turns into gas that forms a big, visible tail.

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But a comet doesn't come with an endless supply of ice. It has a rocky core underneath, constantly losing the layers of ice that cover it. Every time it passes the sun, the cloud of gas around it -- called a coma -- is going to be a little bit smaller. Eventually, the coma will disappear, leaving something that looks a lot like an asteroid. It seems that's probably the case for our Halloween visitor.

(NAIC-Arecibo/NSF)
(NAIC-Arecibo/NSF)

"We found that the object reflects about six percent of the light it receives from the sun," Vishnu Reddy, a research scientist at the Planetary Science Institute, said in a statement. "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. That suggests it could be cometary in origin -- but as there is no coma evident, the conclusion is it is a dead comet."

This zombie comet is about 2,000 feet across, and it rotates once every five hours. Scientists have playfully suggested that it looks like a skull, because apparently undead comets aren't Halloween-y enough to satisfy them.

The comet will come nearly as close to Earth as the moon (1.3 lunar distances, to be precise) at about 1 p.m. Eastern time. So when you're out trick or treating, just remember: There's a zombie in the sky. But it's almost certainly not coming to get us.

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