JAXA Forms Special Team to Protect Earth from Asteroids

Asteroids drifting through space occasionally strike Earth. Japan Aerospace Exploration Agency (JAXA) has intensified its efforts to prevent a potentially catastrophic event. In April, JAXA established a planetary defense team for the early detection and avoidance of hazardous asteroids.

A European spacecraft equipped with devices from this team is scheduled to launch in October. It aims to participate in an on-site investigation of a collision experiment conducted in 2022. With the asteroid Apophis set to pass near the geostationary orbit in five years, JAXA is rapidly developing a system to rival those of the United States and Europe.

Asteroid Injures 1,500 in 2013

To date, approximately 35,000 asteroids on trajectories approaching Earth have been identified. Most of the asteroids over ten kilometers in diameter — similar to the one believed to have caused the dinosaur extinction 65 million years ago — have already been discovered. This reduces immediate concerns about collisions of this magnitude. However, the number of smaller asteroids, those under one kilometer in diameter, continues to grow.

While asteroid sizes vary, even those larger than ten meters across can cause significant damage upon impact.

In 2013, a 17-meter-wide asteroid impacted Chelyabinsk Oblast in southern Russia, exploding mid-air at supersonic speeds. Although the resulting debris caused only minor direct damage, the powerful shockwave shattered windows across the area, injuring about 1,500 people.

Another historic event, the Tunguska Explosion of 1908 in Russia, destroyed an area of approximately 2,000 square kilometers. This is three times the size of Tokyo's 23 wards. The asteroid responsible was estimated to be around 60 meters wide, and the energy released by the impact was equivalent to that of one thousand atomic bombs dropped on Hiroshima.

The Barringer Crater in Arizona measures over one kilometer in diameter and about 200 meters deep. It is believed to have formed from the impact of an asteroid about 50 meters across.

Meanwhile, in Japan, the Narashino meteorite is remembered by many. In 2020, its fragments fell in northwest Chiba Prefecture. Although the asteroid was said to be several tens of centimeters in size, the fragments did not cause significant damage.

*Barringer Crater in Arizona, United States, June 2023. (Provided by Makoto Yoshikawa)*

Detecting Asteroids

Planetary defense involves two critical phases to protect Earth from asteroid impacts.

The first phase focuses on detecting asteroids that are on a collision course with Earth, tracking their trajectories, and calculating their orbits. If a potential collision is predicted, researchers assess the asteroid's physical properties to devise effective avoidance strategies.

To date, eight asteroids on a direct path to Earth have been identified in advance, all by teams in the US or Europe. The earliest detection occurred in 2008 when a two- to three-meter-wide asteroid was identified 20 hours before it struck northern Sudan. More recently, in January 2024, an asteroid approximately one meter in diameter was spotted just three hours before it impacted western Berlin.

The second phase of planetary defense involves implementing strategies to either deflect the asteroid or minimize its potential damage. This could include techniques to artificially alter the asteroid's orbit or, if necessary, coordinating large-scale evacuations.

Altering an Asteroid's Orbit

With the current technology, the feasible method for altering an asteroid's orbit involves crashing a spacecraft or similar object into it. To explore this approach, the US and Europe have jointly developed an experimental program called Asteroid Impact and Deflection Assessment (AIDA), which involves two spacecraft: NASA's DART and ESA's Hera.

In 2022, DART successfully impacted the asteroid Dimorphos at six kilometers per second. The asteroid was around 160 meters in diameter and DART weighed approximately 500 kilograms. Observations following the collision confirmed changes in the asteroid's orbit.

Scheduled for launch in October 2024, Hera is set to impact asteroid Dimorphos in December 2026. The spacecraft carries an advanced infrared camera developed by JAXA designed to examine the asteroid's temperature and physical characteristics. It is an upgrade from the camera used on the Hayabusa2 spacecraft.

The insights gained from this mission will be instrumental in shaping strategies for future planetary defense missions. It should help provide a practical framework for real-world applications.

Early Detection of Small Asteroids

The recently formed Planetary Defense Team at JAXA is expected to act as a liaison for collaboration with agencies like NASA and ESA. This team comprises around twenty specialists in asteroid exploration and orbit calculation. It also includes members from the Hayabusa and Hayabusa2 missions, which successfully retrieved asteroid samples.

One of the team's focuses is the ongoing observation of asteroids from the Bisei Spaceguard Center in Okayama Prefecture. However, the center's telescope, with a 20-centimeter aperture, struggles to detect asteroids smaller than several tens of meters in diameter beyond the Moon's orbit.

To address this, the goal is to maintain constant monitoring with telescopes that have at least a one-meter diameter. This would enable the detection of even small asteroids just a few meters across, providing more time to prepare if dangerous asteroids are detected at a great distance from Earth.

Asteroid Apophis

Currently, the asteroid Apophis is drawing significant attention. Measuring approximately 340 meters in diameter, it is projected to pass extremely close to Earth on April 13, 2029, coming closer than the geostationary orbit. The asteroid is not expected to impact Earth. However, if it were to impact, it could cause catastrophic regional damage, affecting areas much larger than individual cities.

This event will mark the first time in observed history that an asteroid of this size will pass so close to Earth. Therefore, it offers a unique opportunity to study an asteroid in detail without the need for a spacecraft. Additionally, it allows for testing current technologies designed to impact and potentially alter an asteroid's orbit.

A key focus of asteroid exploration is to understand how Earth's gravity affects an asteroid's surface, internal structure, rotation, and orbit.

Makoto Yoshikawa, Associate Professor of Celestial Mechanics at JAXA and head of the Planetary Defense Team, commented, "This is an extremely rare event. While Apophis will not collide with Earth, the data collected will enhance our preparedness for future encounters with other asteroids."

(Read the article in Japanese.)

Author: Shinji Ono, The Sankei Shimbun