Original title: an asteroid the size of a football field nearly hit the earth this month, and NASA didn't warn
On September 16, the asteroid 2021 SG passed 153000 miles from the earth, about half the distance between the earth and the moon, but NASA didn't discover it until the next day. NASA said recently that it will launch a telescope to detect such dangerous space rocks in the future.

Size comparison of asteroid 2021 SG.
It is reported that the space rock is between 138 and 308 feet in diameter, or larger than a football field. It is roughly the same size as the statue of liberty and flies close to the earth at a speed of more than 53000 miles per hour.
Paul chodas, director of NASA's near earth object Research Center (cneos), said that the space telescope (NEO surveyor), known as the "near earth object surveyor", would "very likely" find the asteroid in different parts of its orbit and early in its near earth orbit in the future.

The asteroid has a strange orbit, and NASA failed to observe it close to the earth as soon as possible.
The telescope is scheduled to launch in 2026. It will be placed between the earth and the sun to better discover space rocks.
Jordas said that 2021 SG was not detected at first because its orbit was strange, extending from the orbit of mercury to the asteroid belt and passing through the orbit of Mars.

Schematic diagram of asteroid passing the earth at close range.
It is reported that if the asteroid enters the earth's atmosphere, it will produce a "huge and impressive meteor". Since it was last in Canada and Greenland, if it entered the atmosphere, given that Canada has a population of more than 37 million, it is likely to cause significant damage.

Near Earth Asteroid data observed in recent years.
According to the data released by NASA, there are more than 26000 near Earth Asteroids in space, of which only about 10000 are more than 140 meters (450 feet) in size.
Although the asteroid 2021 SG passes through the earth within 0.05 astronomical units (AU), NASA only considers it a "potential danger" because it is less than 460 feet in diameter.
However, it is four times larger than the space rock disintegrated over Chelyabinsk, Russia on February 15, 2013. The rock injured 1500 people and the shock wave destroyed windows in six Russian cities.
Text / Nandu reporter Chen Lin