An asteroid the size of a bus safely flew past Earth yesterday morning, ahead of a larger house-sized asteroid that will skim our planet next week.
The first was called 2017 SX17, measuring about 8 meters (26 feet) wide. It passed within 87,000 kilometers (54,000 miles) of our planet at 6.20am EDT (10.20am GMT) yesterday, October 2, about one-third the distance of the Moon.
While it came close, the asteroid posed no threat to Earth. NASA tracks asteroids of this size and 2017 SX17 had no chance of hitting us on its 476-day orbit around the Sun.
However, it was only spotted on September 24, 2017. That’s fairly late, and serves as a gentle reminder that we need to get better at tracking asteroids. Thousands of near-Earth objects (NEOs) like this and smaller remain undetected.
On October 12, we’ll have an encounter with an even bigger asteroid. Called 2012 TC4, it was discovered back in 2012 and is thought to be up to 39 to 88 feet (12 to 27 meters) across in size.
It will pass by closer, about 43,500 kilometers (27,000 miles) from our planet, or one-sixth the distance of the Moon. Again, it's unlikely to hit us, but reminds us of the dangers asteroids could pose. One this size was responsible for the explosion over Chelyabinsk in Russia in 2013 that injured hundreds.
“We know the orbit of 2012 TC4 well enough to be certain that it won’t hit Earth,” said Paul Chodas, manager of the Center for Near-Earth Object Studies (CNEOS), at NASA’s Jet Propulsion Laboratory, Pasadena, California, in a statement.
Astronomers were actually using this asteroid to conduct an experiment on tracking asteroids. While we knew it wouldn’t hit Earth, the exact flyby and size of 2012 TC4 were unknown. So, when it started approaching Earth in the summer, scientists began searching for it and tracking it, to get better constraints on its properties.
A few other asteroids have had close shaves with Earth this year, but 2012 TC4 is the closest. It will fly past our planet quite a few more times over the next 100 years, but it only has a 0.013 percent chance of hitting us in that time. So we’re pretty safe for now.