What would happen if the asteroid Ryugu hit Earth?

Scientists have calculated what would happen if the asteroid Ryugu were to hit our planet. Predicting the outcome of such a collision was made possible thanks to the analysis of samples returned to Earth by the Hayabusa2 spacecraft of the Japanese Aerospace Exploration Agency (JAXA).

Presenting the results of the calculations at the 8th Planetary Defense Conference in Vienna, Austria on Monday, April 4, JAXA’s Department of Solar System Sciences professor Satoshi Tanaka emphasized the importance of conducting such assessments in efforts of planetary protection even for asteroids like Ryugu that currently do not pose an impact risk.

Launched in December 2014, Hayabusa2 reached Ryugu, an approximately 0.6-mile (900-meter) wide asteroid located 186 million miles (300 million kilometers) from Earth in June 2018, after traveling for 42 months. In addition to collecting samples, which were returned to Earth in 2020, Hayabusa2 also landed several rovers on the asteroid and hit the space rock with two projectiles.

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“Hayabusa2 succeeded in an experiment in which two 1 kg [2.2 pounds] the projectiles were fired at a speed of 2 kilometers per second [1.2 miles per second] resulting in the formation of a crater approximately 20 meters [66 feet] in diameter,” Tanaka said. “The cohesive strength of the rock was thought to be very low. The density is slightly higher than water with a very high estimated porosity.”

Based on these facts, Ryugu, which is currently estimated to be no closer to Earth than about 62,000 miles (100,000 kilometers), is considered to be a debris pile asteroid with a low mechanical strength compared to normal rocks. This means that if the asteroid were to ever head for Earth, scientists would have to be very careful to prevent it from breaking up if they try to deflect it using something like the DART impactor which in September 2022 hit the asteroid moon Dimorphos.

Without deflection interference, Tanaka explained, if asteroid Ryugu were to head for Earth and enter the planet’s atmosphere at an angle of 45 degrees and at a speed of about 38,000 miles per hour (17 kilometers per second), the cluster asteroid the rubble would explode. at an altitude of about 25 to 21 miles (40 to 35 km) above the planet’s surface.

This would result in an “air burst” similar to the one seen over Russia in February 2013 when the Chelyabinsk meteor exploded at an altitude of about 19 miles (30 kilometers) above Earth. The result of the Chelyabinsk explosion was a bright flash of light and an atmospheric explosion equal to the explosion of 400-500 kilotons of TNT. This is 33 times the energy released by the atomic bomb that destroyed Hiroshima at the end of World War II.

The Chelyabinsk blast injured almost 1,500 people, mostly due to the amount of debris and broken glass it produced. At just 66 feet in diameter, the Chelyabinsk meteor was the largest object to enter Earth’s atmosphere from space since 1908, but is still only a fraction of Ryugu’s size.

Tanaka noted that if Ryugu were to break up in the atmosphere above Earth, we currently don’t know enough about the asteroid’s elastic strength to predict the size of the pieces that would fall on our planet.

“Ryugu’s drag force may be more than two orders of magnitude greater than current estimates which could affect its effects on Earth,” Tanaka concluded. “The return sample is in the process of completing initial analysis. Exploration of internal fractures will be important in the future to more accurately assess the impact [of asteroids like Ryugu] on the ground.”

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