Thread by @BiIndia

A car-sized #asteroid flew within 1,830 miles of #Earth over the weekend — the closest pass ever — and we didn't see it coming

businessinsider.in/science/news/a…

A car-sized #asteroid flew within about 1,830 miles (2,950 kilometers) of #Earth on Sunday.

That's a remarkably close shave — the closest ever recorded, in fact, according to asteroid trackers and a catalog compiled by Sormano Astronomical Observatory in Italy.

Because of its size, the space rock likely wouldn't have posed any danger to people on the ground had it struck our planet. But the close call is worrisome nonetheless, since astronomers had no idea the #asteroid existed until after it passed by.

"The asteroid approached undetected from the direction of the sun," Paul Chodas, the director of NASA's Center for Near Earth Object Studies, told Business Insider. "We didn't see it coming."

Instead, the Palomar Observatory in California first detected the space rock about six hours after it flew by #Earth.

#NASA knows about only a fraction of near-Earth objects (NEOs) like this one.

Many do not cross any telescope's line of sight, and several potentially dangerous asteroids have snuck up on scientists in recent years. If the wrong one slipped through the gaps in our NEO-surveillance systems, it could kill tens of thousands of people.

2020 QG flew over the Southern Hemisphere

This recent near-Earth asteroid was initially called ZTF0DxQ but is now formally known to astronomers as 2020 QG. As far as space rocks go, 2020 QG wasn't too dangerous.

Not dangerous, but definitely not welcome

Telescope observations suggest the object is between 6 feet (2 meters) and 18 feet (5.5 meters) wide — somewhere between the size of a small car and an extended-cab pickup truck.

But even if it was on the largest end of that spectrum and made of dense iron (most asteroids are rocky), only small pieces of such an asteroid may have reached the ground, according to the "Impact Earth" simulator from Purdue University and Imperial College London.

Such an asteroid would have exploded in the atmosphere, creating a brilliant fireball and unleashing an airburst equivalent to detonating a couple dozen kilotons of TNT.

That's about the same as one of the atomic bombs the US dropped on Japan in 1945. But the airburst would have happened about 2 or 3 miles above the ground, so it wouldn't have sounded any louder than heavy traffic to people on the ground.

#NASA is actively scanning the skies for such threats, as Congress has required it to do since 2005. However, the agency is mandated to detect only 90% of "city killer" space rocks larger than about 460 feet (140 meters) in diameter.

In May 2019, #NASA said it had found less than half of the estimated 25,000 objects of that size or larger. And of course, that doesn't count smaller rocks such as the Chelyabinsk and 2019 OK asteroids.

Objects that come from the direction of the sun, meanwhile — like 2020 QG — are notoriously difficult to spot.

NASA is in the early stages of developing a space telescope that could detect asteroids and comets coming from the sun's direction.

#NASA's 2020 budget allotted nearly $36 million for that telescope, called the Near-Earth Object Surveillance Mission. If funding continues, it could launch as early as 2025.