5 of the most dangerous asteroids for Earth

To prevent asteroids from colliding with the Earth and avoiding deadly consequences, NASA's Center for Near-Earth Object Studies (CNEOS) uses the Sentry impact monitoring system. Which of them is the most dangerous, how likely is an impact and how destructive will it be?

To understand the current situation, scientists are performing a long-term analysis of possible future orbits of potentially dangerous asteroids. Live Science tells about five of them.

About 66 million years ago, an asteroid the size of a city collided with the Earth. The impact released energy equivalent to the detonation of 72 trillion tons (65 metric tons) of TNT, leaving a 180-kilometer-wide scar on the modern-day Yucatan Peninsula in Mexico.

The most infamous effect of this asteroid, dubbed the Chicxulub impactor, was the death of the dinosaurs, along with about three-quarters of the Earth's species, in an event called the Cretaceous-Paleogene extinction. To prevent such catastrophic impacts, NASA's CNEOS uses the Sentry impact monitoring system.

Bennu

Size: 0.49 kilometers

Mass: 74 million tons (67 million metric tons)

Discovered in September 1999 and officially designated as "101955 Bennu (1999 RQ36)", the near-Earth asteroid Bennu now poses the greatest risk of impacting our planet. However, not soon at all. NASA scientists estimate that Bennu will approach Earth on September 24, 2182, at which time there is a 0.037% - or 1 in 2700 - chance that the asteroid will collide with our planet.

In preparation for this, scientists are learning as much as they can about this carbon-rich asteroid, which is believed to have separated from a larger asteroid between 2 billion and 700 million years ago. On September 24, 2023, NASA's OSIRIS-REx spacecraft returned a sample of Bennu to Earth, and the space rock was analyzed by teams of researchers from around the world. Initial results suggest that Bennu contains the building blocks of life, including the simple amino acid glycine, as well as many water minerals. This suggests that Bennu's parent body witnessed many water-related episodes before it eventually split.

If Bennu collides with the Earth, it will release energy equivalent to the explosion of 1.4 billion tons of TNT, causing regional but not global devastation. If a collision occurs in a densely populated area, Bennu could cause millions of deaths.

29075 (1950 DA)

Size: 1.3 kilometers

Mass: 78 million tons (71-meter tons)

The second most hazardous object is asteroid 29075 (1950 DA), which was lost after its first discovery in February 1950 and rediscovered 50 years later. It is believed that 1950 DA is an asteroid of loose debris with a high content of iron and nickel. Currently, 1950 DA has a 0.0029% - or 1 in 34,500 - chance of colliding with Earth on March 16, 2880.

If the 1950 DA hits Earth, it will release the energy equivalent to 75 billion tons of TNT, which is enough to cause a global catastrophe that could potentially wipe out humanity.

2023 TL4

Size: 0.33 kilometers

Weight: 47 million tons (43 million metric tons)

Asteroid 2023 TL4, discovered in 2023, shows that it can immediately become one of the most potentially dangerous. Based on observations collected between October 8 and 19, 2023, astronomers estimate that 2023 TL4 has a 0.00055% chance - or 1 in 181,000 - of hitting Earth on October 10, 2119. If such an impact occurs, 2023 TL4 will release energy equivalent to the detonation of 7.5 billion tons of TNT.

2007 FT3

Size: 0.34 kilometers

Weight: 54 million tons (49 million metric tons)

2007 FT3 is designated as a "lost asteroid" because astronomers have not seen it since 2007. Now the orbit of this object is not very constrained, but NASA predicts that the asteroid has a 0.0000096% - or 1 in 10 million - chance of colliding with us on March 3, 2030. The asteroid has a slightly lower probability of 0.0000087% - or 1 in 11.5 million - of colliding with Earth on October 5, 2024.

If such an impact were to occur in 2024 or 2030, FT3 would release energy equivalent to the detonation of 2.6 billion tons of TNT, enough to cause massive regional damage but not to trigger a global catastrophe.

1979 XB

Size: 0.66 kilometers

Weight: 390 million tons (354 metric tons)

Another lost asteroid, 1979 XB, hasn't been seen by scientists for about 40 years, and so its orbit is also poorly understood. From what CNEOS scientists do know, the asteroid, which was first observed on December 11, 1979, has a 0.000055% - or 1 in 1.8 million - chance of colliding with Earth on December 14, 2113. Such a collision would release the same amount of energy as the detonation of 30 billion tons of TNT.

No longer dangerous: 99942 Apophis

Size: 0.34 kilometers

Mass: 27 million tons (24 metric tons)

It's hard to talk about risky asteroids without mentioning 99942 Apophis. This asteroid - with an appropriately apocalyptic name that recalls Apep, the enemy of the ancient Egyptian sun god Ra - has been at the top of the risky asteroid table for almost two decades.

Discovered in June 2004, Apophis was quickly recognized as one of the most dangerous asteroids that could collide with Earth. However, that changed in 2021 when a radar surveillance campaign better constrained the asteroid's orbit. This made astronomers to conclude that the 340-meter-wide Apophis poses no danger to Earth for at least 100 years. It is now in the "Removed Objects" section of the Sentry Risk table.

This means that skywatchers will be able to observe Apophis during its close approach in 2029 when it passes within 32,000 km - closer than some satellites - with binoculars and telescopes and without fear that its return in 2036 and 2068 will endanger the planet.

So what are the risks?

The thought of an asteroid falling is frightening, but all of the space rocks on this list are labeled "zero" or "white" on the Torino Impact Hazard Scale. The Turino scale, adopted by the International Astronomical Union in 1999, gives asteroids a number from 0 to 10, indicating both the risk of collision and the consequences of such an impact.

Level 0, the white zone, indicates zero risk of impact, or at least a risk so low as to be zero. This level applies not only to asteroids that miss the Earth but also to small objects from space that will burn up in the atmosphere and therefore pose no threat.

Levels 8 through 10, on the other hand, are in the red zone, representing asteroids that will definitely impact the Earth, with consequences ranging from localized destruction (level 8) and unprecedented regional destruction (level 9) to global climate catastrophe (level 10) that could threaten the future of civilization.

Currently, there are no facilities in the Sentry Risk table that are approximately level 0. Bennu and 1950 DA do not have Torino ratings because their projected impact is more than 100 years in the future. According to NASA, "there is currently no known significant collision threat over the next hundred years or more."

Of course, there could still be potentially dangerous objects out there waiting to be discovered - indeed, thousands of potential "city killers" and even some "planet killers" could be hiding in the sunlight - which is why CNEOS is always vigilant in its search for near-Earth asteroids.

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