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This possibility stems from the study of two asteroids, named 2021 PH27 and 2025 GN1, which share an almost identical orbit around the Sun. Their similar spectral composition and common trajectory immediately caught the attention of scientists. These bodies belong to the Atira group, a small family of asteroids whose orbits lie entirely within Earth's orbit, making them harmless to us.
Artist's representation of an asteroid fragmenting into several pieces.
Credit: NASA/JPL-Caltech
To trace their history, a team led by Albino Carbognani of the Italian National Institute for Astrophysics modeled the trajectories of these objects over a period of 100,000 years. Their simulations indicate that these two space rocks were once a single object. To understand their separation, scientists examined the orbital past of their common ancestor, which passed within just 15 million kilometers (about 9.3 million miles) of the Sun several millennia ago.
At such proximity, the intense heat caused cracks to appear on the surface, weakening the asteroid's internal structure. Simultaneously, the YORP effect, a phenomenon where the emission of thermal radiation alters an object's rotation, came into play. This dual action eventually caused the celestial body to spin so rapidly that it fractured into two distinct pieces between 17,000 and 21,000 years ago.
The debris and dust released during this event later formed a diffuse cloud. According to calculations, this cloud is expected to cross Venus's orbit in July, which could generate a meteor shower on the planet. However, from our planet, only the brightest among them might be visible.
Direct observation of this phenomenon from Venus's environment would be ideal, but no current space mission is capable of doing so. Upcoming projects, such as the European EnVision mission planned for the 2030s, or NASA's DAVINCI and VERITAS missions, could one day record such an event. This would allow analysis of how asteroids influence planetary atmospheres.
On Earth, famous meteor showers, like the Geminids, often originate from comets, but asteroids can also be their source.
The YORP effect
The YORP effect is a process that alters the rotation of small celestial bodies like asteroids. It occurs when these objects absorb light from a star like the Sun on one side and re-emit the heat as infrared radiation from the other. This emission acts as a tiny but constant thrust, capable of gradually accelerating or slowing down the asteroid's rotation speed.
The name YORP honors four scientists: Yarkovsky, O'Keefe, Radzievskii and Paddack, who contributed to its discovery. It is particularly effective on small asteroids or those with an irregular surface, as the uneven distribution of heat amplifies the effect. Over time, this acceleration can become significant.
In the case of the parent asteroid studied, the YORP effect played a decisive role. Combined with the fractures caused by solar heat, it increased the rotation to a breaking point. This mechanism explains how seemingly stable bodies can fragment without major gravitational intervention from other planets.
Asteroids of the Atira group
Asteroids of the Atira group are a special class of objects whose orbits lie entirely within Earth's orbit. This means they never cross our planet's path, making them safe in terms of impact risk. Their name comes from the asteroid Atira, the first discovered in this category, and they are relatively rare in the Solar System.
These asteroids orbit very close to the Sun, with short revolution periods. For example, 2021 PH27 and 2025 GN1 complete a full orbit of our star in just 115 days. Their proximity to the Sun exposes them to extreme temperatures and intense gravitational forces.
Atira asteroids are difficult to observe from Earth due to their position in the sky, often obscured by the Sun's glare. Their discovery relies on specialized telescopes and observations during twilight. Studying these bodies helps map the diversity of orbits and understand the formation of the inner planets.