Warehouse-sized asteroid whipped by Earth and no one saw it coming

A space rock perhaps as large as a football field flew between the Moon and Earth last week, but the large asteroid – cataloged as 2021 SG – wasn’t spotted until the day after it passed. closest to our planet.

As asteroid 2021 SG returns safely to deeper space, it offers a brief moment of deja vu to sky-watchers who may remember the great meteor that was not seen until. what he exploded in 2013 over Chelyabinsk, Russia.

This meteor was estimated to be only about a quarter of the diameter of 2021 SG, and yet it was large enough to create a shock wave that blew thousands of windows into the city below, injuring hundreds. Asteroid 2021 SG is not only much bigger, but it is also moving at an impressive speed of over 53,000 mph (85,295 km / h).

2021 SG safely passed us on September 16, but at a relatively close distance – astronomically speaking – of around 153,000 miles (246,000 km). If it had entered Earth’s atmosphere, it likely would have caused destruction, especially if it had struck near a populated area.

The Chelyabinsk meteor and the 2021 SG asteroid signal a literal blind spot when it comes to monitoring so-called near-earth objects: the sun. As NASA Solar System Ambassador Eddie Irizarry and EarthSky Editor-in-Chief Deborah Byrd explain, the two space rocks were not detected when they approached us because they were coming from the direction of the sun.

Astronomers, using large telescopes, sky surveys and other advanced technology, have become very good at locating, cataloging and tracking all kinds of objects in space, right down to the tiny pieces of old orbiting satellites. . But at the moment, there is simply no good way to keep an eye on objects – even the largest ones – that are approaching us from the direction of our favorite fireball.

Fortunately, a fix is ​​on the way. NASA plans to launch its NEO Surveyor spacecraft in 2026, which will be stationed at a location in space between Earth and the sun so that it can detect objects we cannot see from here.

In the meantime, we just need to get through the next half decade without factoring in the major arrival of the direction of our nearest star.