What are potentially dangerous asteroids and is an asteroid predicted to hit Earth?

An asteroid twice the size of the Empire State Building will approach Earth on January 18.

The asteroid, 7482 (1994 PC1), will pass within about 1.2 million miles of Earth.

This means that the asteroid is close enough and large enough, with a diameter of about 1,000 meters, to be defined as a Potentially Hazardous Asteroid (PHA) by NASA’s Center of Near-Earth Object Studies (CNEOS) . This is despite the fact that 7482 (1994 PC1) has virtually no risk of impacting Earth.

There are two main reasons why an asteroid is labeled a PHA, and these space objects can be classified as “potentially dangerous”, even though a collision course with Earth is ruled out for the foreseeable future. Go.

CNEOS defines a PHA as a near-Earth object (NEO) that comes approximately 4.6 million miles or closer to Earth and has an absolute magnitude of 22.0 or less. Absolute magnitude is the brightness of an object as seen from Earth if it is placed within 1 astronomical unit (AU) or about 93 million miles of our planet.

This may seem like an odd way of defining an object as dangerous, but such an absolute magnitude would indicate a diameter of about 140 meters.

University of Illinois Urbana-Champaign astronomy professor and president Leslie Looney told the Illinois News Bureau: “Anything greater than 140 meters in diameter can cause major damage to cities or coasts, so those with orbits that cross Earth’s orbit can cause major damage.” Any NEO is classified as a potentially dangerous object.”

Looney further pointed out that of the 28,000 NEOs that NASA is aware of, about 2,000 are classified as PHAs. Neither of these objects is predicted to have an impact on Earth in the next century.

“None of them are likely to affect the planet in the next 100 years, but we still watch their orbits for any changes,” Looney continued. “The orbital paths of the NEOs that will be near Earth in more than 100 years cannot be predicted very well.”

It is the responsibility of the NASA Jet Propulsion Laboratory (JPL) Automated Sentry Monitoring System to track these objects and monitor the risks they pose to Earth.

JPL and CNEOS rank PHAs in their sentinel risk tables listing the likelihood of impact and the number of possible impacts that NEOs can make. Newly discovered NEOs are usually placed on the list to be removed only because their orbits are studied in more detail and better constrained.

For 17 years, the object that sat on top of the Sentry risk table was the asteroid Apophis. In April 2029, the 340-meter-wide (over 1,110 ft) asteroid will pass within 19,000 miles of Earth. This would bring it so close to our planet that it would be closer than most geostationary satellites, and its proximity and size mean it would be visible to the naked eye from Earth’s surface.

For some time, astronomers believed that during this close passage, Apophis might encounter a so-called gravitational keyhole that could affect its orbit in such a way that its next pass would result in an impact in 2068. may fall.

After it was ruled out by CNEOS in 2021, a team was finally able to determine that Earth was safe from impacts in 2068 and for at least the next century. But just because Earth is protected from the occupants of this long sentry impact table doesn’t mean we should sit back and relax.

In 2021, NASA launched the Double Asteroid Redirection Test (DART) spacecraft, a test mission that will determine whether kinetic effects can divert an asteroid. DART will strike the smaller member of the double asteroid system Dimorphos and Didymos later this year at about 15,000 mph to see how it affects its orbit.

“However, it is important to note that large impacts have hit Earth in the past—ask any dinosaurs—and the planet will be affected by large impacts in the future,” concluded Looney. “It’s not a matter of if, but a matter of when. But don’t panic. It’s not likely to happen anytime soon.”

An asteroid approaches Earth. NASA’s CNEOS defines an asteroid as “potentially dangerous” if it comes within about 4.6 million miles of the planet.