(CNN) -- It's as if the universe itself is trying to get in on Halloween.
NASA says a large space rock set to fly narrowly by Earth Saturday morning -- the early hours of Halloween -- looks like a skull. Scientists say that the rock is -- wait for it -- a "dead" comet. In NASA terminology, that means it has "shed its volatiles" that would produce the visible tail seen on some comets.
As it misses Earth by about 300,000 miles (slightly farther away than the moon), the skull-shaped asteroid, named 2015 TB145, will be visible to those with good telescopes.
Calling it "one of the best radar targets of the year," a Jet Propulsion Laboratory report on the asteroid said that "the flyby presents a truly outstanding scientific opportunity to study the physical properties of this object."
As viewed from Earth the asteroid is traveling through Orion on October 30-31.
It's a good thing it will miss, though. The asteroid is estimated to be 600 meters wide and traveling at 78,000 mph. By comparison, the meteorite that exploded in the sky over Chelyabinsk, Russia, in 2013 was about 20 meters wide.
Asteroid 2015 TB145 will be the biggest known object to pass so close to the Earth until 2027.
Of course, the key phrase there is "known object." Until October 10, the space agency didn't know about 2015 TB145; more attention was on asteroid 2009 FD, which passed within about 4 million miles of Earth on October 29.
On October 10, asteroid 2000 FL 10, which had some people crying doom, missed Earth by 15 million miles.
JPL runs NASA's Near Earth Object Office to keep track of such celestial visitors. You can follow its news on Twitter at @asteroidwatch.
This isn't the first time an asteroid has come close to our planet in late October. On October 30, 1937, the binary asteroid Hermes -- an alarmingly regular visitor to these parts -- came within 500,000 miles of Earth. Hermes' two parts are each about 600 to 900 meters wide.
However, Hermes' orbits have been well-plotted in recent years. According to a JPL engineer quoted in a 2003 Cornell article, "there is no cause for worry in our lifetimes."AlertMe