A skyscraper-sized asteroid will speed past Earth from an uncomfortably close distance this Halloween.
Although 310,000 miles away may not sound close, the giant space rock is zooming by only a little farther away than the moon is from the Earth — close enough to spot with an amateur telescope, says NASA. It's also important to remember the 1,300-foot-wide asteroid, called 2015 TB145, is moving about 45 times faster than a speeding bullet.
This is the biggest object that's neared our home planet since 2006, but it's by no means the only threat NASA is keeping a close eye on. Thousands exist in the vicinity of Earth, and some of them are downright dangerous. If 2015 TB145 struck the Earth, for example, it could flatten New York City. The impact crater alone would likely cover Manhattan.
NASA's formal way of cataloging such threats is through its near-Earth object (NEO) observation program. If an asteroid or comet passes within 1.3 astronomical units of the sun (1 au is 93 million miles, or the distance from the Earth to the sun), then NASA carefully tracks it as an NEO.
As of October 24, 2015:
- we've discovered 13,271 NEOs
- 877 of them are asteroids more than 1 kilometer (3,280 feet) wide
- 1,637 of them are classified as potentially hazardous
An object is "potentially hazardous" if it will come within 0.05 astronomical units of Earth (a little more than 4.5 million miles).
We can't easily see such asteroids; most resemble dim stars in space. But data from observatories have helped scientists map out just how many are around Earth, and it looks a little terrifying.
Take the following map by Armagh Observatory, for example. The big yellow circle is Earth. All the green dots represent asteroids at a safe distance, while red and yellow dots represent potentially dangerous asteroids that could spell trouble for us:
This video by Scott Manley is similar, but in animated form. It shows the solar system's four inner planets (blue), and 30 years' worth of asteroid discoveries.
Objects that cross Earth's orbit are red, those that cross the orbit of Mars are yellow, and those in the Asteroid Belt (for reference) are green:
Luckily, all of the known NEOs we've spotted have less than a 0.01% chance of hitting Earth within the next 100 years, according to NASA, and the next dangerous encounter won't happen until 2027.
However, NASA didn't know about this super-close Halloween asteroid until October 10. That's likely because 2015 TB145 has an unusual orbit, making it difficult to spot from afar. This begs the question: How many other dangerous asteroids exist in space that we have yet to spot?
Right now NASA is preparing to send a spacecraft to an asteroid, and the agency hopes to eventually tow one into orbit around the moon and send astronauts to explore it. Scientists are also working out ways to either redirect or destroy an asteroid if we ever find one that's headed straight for Earth. The United Nations even has a special subcommittee dedicated to the task.
But for now, at least, celebrate not in any known and immediate danger of incoming doom. And if you have a telescope handy, look for the Halloween asteroid passing through the constellation of Orion around 1:05 p.m. EDT on October 31.
