On Halloween, Earth will get an erratic visitor from deep space. A newly detected asteroid — named 2015 TB145 — will pass within nearly 300,000 miles of our planet on October 31st. That's 1.3 times the distance between the Earth and the Moon. It's a pretty big asteroid too, with a diameter somewhere between 950 and 2,100 feet across — somewhere between the height of the Chrysler Building and the Shanghai Tower. As far as we know, it's the closest an object of this size will get to our planet until asteroid 1999 AN10 comes within just one lunar distance of Earth in 2027.
Before you panic, NASA scientist Davide Farnocchia says there's absolutely no chance that 2015 TB145 will ruin your trick-or-treating plans; it's just zipping by for a quick hello. In fact, we get visits like these from asteroids all the time. NASA has cataloged around 8,000 near Earth asteroids of this size or larger — however, we only get close visits from objects of this size about once per decade. The last big asteroid to pass so close to Earth was asteroid 2005 YU55, a 1,300-foot wide rock that passed within 0.85 lunar distances in 2011.
There's absolutely no chance that 2015 TB145 will ruin your trick-or-treating plans
2015 TB145 is also a bit unusual because it's moving super fast. It will hurtle past Earth at nearly 22 miles per second, a much higher velocity than the average asteroid speed of 6 miles per second. This asteroid's orbit is deemed "extremely eccentric," meaning it's path is much more elliptical than the normally circular orbits asteroids take.
Additionally, NASA only found about 2015 TB145 last week, after it was spotted by the Pan-STARRS 1 telescope on October 10th. Farnocchia says it's completely normal to find asteroids like this so late. The reason for the short warning time is because this space rock isn't considered that big to NASA. The space agency's mainly concerned with finding asteroids that are much larger — usually more than 3,200 feet wide. Those are the objects that could potentially wipe us out if they collided with Earth. NASA-funded surveys are constantly observing the night sky to find these "extinction-level" asteroids, and we've mapped out an estimated 90 percent of them so far. There are no threats of these larger asteroids hitting us within the next century — that we know about, anyway.
2015 TB145 would fall somewhere between "Destruction on a national scale" and "Destruction on a European scale" if it were to hit us. But it won't. (Source: The International Schiller Institute)
Still, if 2015 TB145 were to hit us (reminder: it won't), it wouldn't be fun. If the asteroid's diameter is at the smaller end of its estimated range, the asteroid could cause an extremely large regional disaster. At the higher end, we'd be just below a global catastrophic event. You can play with this fun calculator to see how different-sized asteroids would destroy Earth.
Although NASA has a pretty good map of many of the killer asteroids out there, there are still about 10 percent that the space agency doesn't know about. Other organizations hope to increase our planet's knowledge of potential threats, in order to spot a doomsday space rock way before it's scheduled to hit us. The B612 Foundation, for example, wants to launch a space telescope for the sole purpose of looking for these types of asteroids, giving us ample warning time to mount a defense in case one is headed our way.