Zero Genie

A small asteroid flew very close to Earth on Thursday night, less than a week after astronomers discovered the object.

The asteroid, named 2023 BU, was scheduled to pass over the southern tip of South America at 7:27 p.m. Eastern time. The asteroid is fairly small — less than 30 feet across, about the size of a truck — and was best visible in the skies to the west of southern Chile. For space watchers unable to view 2023 BU firsthand, the Virtual Telescope Project broadcast the event on its website and YouTube channel.

The asteroid did not hit Earth but was one of the closest approaches ever by such an object, hurtling past Earth at just 2,200 miles above its surface, according to a news release from the NASA Jet Propulsion Laboratory. This encounter put the asteroid “well within the orbit of geosynchronous satellites,” the statement noted, but the asteroid was not on track to hit any.

2023 BU was unknown to NASA, or anyone, until last Saturday. Gennadiy Borisov, an amateur astronomer in Crimea, noticed the asteroid from the MARGO Observatory, a setup of telescopes that he has used to discover other interstellar objects.

Astronomers then determined 2023 BU’s orbit around the sun and impending trip past Earth using data from the Minor Planet Center, a project sanctioned by the International Astronomical Union. It publishes positions of newly found space objects, including comets and satellites, from information of several observatories worldwide.

In 2020 Leonardo Amaral, an amateur astronomer in Brazil, discovered another near-Earth asteroid, 2020 QU6, while using an observatory near São Paulo. The object came no closer to Earth than 20 million miles — about 84 times the distance between Earth and the moon — but prompted interest in helping amateur astronomers to find and track objects that could pose a threat to the planet.

“The big professional search programs that NASA is funding are doing, by far and large, the heavy lifting in discovering new objects,” said Davide Farnocchia, a navigation engineer at J.P.L. who works with the Center for Near-Earth Object Studies, or CNEOS. “But that doesn’t mean that we cannot use help from additional people, which includes professional astronomers from other countries but also amateur astronomers. We like to get as many as possible so that we can get the best possible estimate of the trajectory.”

There are plenty of objects to find. Most asteroids in the solar system orbit the sun in the region between Mars and Jupiter, more than 3.2 astronomical units — 3.2 times the distance between the sun and Earth — away from and never approaching our planet. Asteroids are considered near-Earth objects if they approach within 1.3 astronomical units, and there are several hundred million objects smaller than 460 feet wide in that category, Dr. Farnocchia said.

To pose any serious threat to Earth, an object would have to be more than a dozen times as large as 2023 BU. Even if a smaller object like 2023 BU were on track to strike Earth, it would probably disintegrate in the atmosphere, perhaps casting some debris as small meteorites.

In 2005, Congress ordered NASA to identify 90 percent of the near-Earth asteroids that were 460 feet wide or larger, capable of destroying a city. In September, NASA’s Double Asteroid Redirection Test, or DART, mission tried out one possible defense against such objects. The spacecraft, which launched in late 2021, made impact with Dimorphos, a 550-foot-wide asteroid millions of miles from Earth. The mission was deemed a success after the rock’s orbit was shortened by 32 minutes.

Dr. Farnocchia noted that a genuinely hazardous asteroid would be both larger and brighter than 2023 BU and so would be spotted much farther in advance of its arrival. He added that objects much smaller than 2023 BU pass close to Earth with some regularity.

“This case might seem exceptional, but in fact, objects of a similar size come this close to Earth about once a year on average,” he said. “So this is not an exceptional event. It’s not an everyday event, but it’s something that happens regularly.”