• Asteroid 2024 YR4 will pass close to Earth on 22 December 2032.
• Over the last two months, ESA’s assessment of its impact probability rose as high as 2.8%.
• Over the last few days, analysts have used new telescopic observations of the asteroid to greatly reduce the chance of impact to 0.001%.
• The rise and fall of the asteroid’s impact probability has followed an expected and understood pattern.

Near-Earth asteroid 2024 YR4 was discovered on 27 December 2024 at the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile. Automated warning systems, such as ESA’s ‘Aegis’, quickly identified that the object had a small chance of potentially impacting Earth in 2032.

2024 YR4 is estimated to be between 40 m and 90 m wide. An asteroid of this size could cause severe damage to a local region if it were to impact Earth and so it attracted the attention of the global planetary defence community and triggered the efforts of international asteroid response groups.

Over the next two months, ESA’s Near-Earth Object Coordination Centre and other institutions used new telescopic observations of the asteroid to refine its orbit and assess the hazard.

At first, the impact probability began to rise, as an increasing percentage of the asteroid’s possible orbits led to an Earth impact on 22 December 2032.

On 18 February, the impact probability reached its peak, with ESA’s assessment reaching as high as 2.8%. However, just the next day, observations made using the European Southern Observatory’s Very Large Telescope cut the impact probability in half.

Over the last few days, new observations have been used to ruled out almost all of the remaining orbits that could have led to an Earth impact.

Asteroid 2024 YR4 has now fallen from Level 3 to Level 0 on the Torino Impact Hazard Scaleand no longer requires significant attention. The asteroid is no longer at the top of ESA’s risk list, and the International Asteroid Warning Network has concluded its related activities.

The rise and fall of this object’s impact risk has followed a well understood pattern. An asteroid’s impact probability often rises at first before rapidly dropping to zero as the uncertainty region representing all of its possible orbits shrinks and moves away from Earth.

The evolution of 2024 YR4’s impact probability can be seen in the GIF above. It closely matches the typical scenario described in ESA’s explanatory video on the topic, seen below.

Planned observations of 2024 YR4 using the NASA/ESA/CSA James Webb Space Telescope will go ahead in the coming months to test the telescope’s ability to improve our estimate of the asteroid’s size.

With the deployment of new asteroid survey technologies, such as ESA’s Flyeye telescopes, we are likely to detect an increasing number of similar objects passing close to Earth that we would have missed in the past.

Understanding the effectiveness of tools such as Webb will assist the planning of the planetary defence response to future hazards.

Quelle: ESA