The comet 67P/Churyumov-Gerasimenko could be younger than expected

The comet 67P/Churyumov-Gerasimenko with its two-lobed shape (Photo ESA/Rosetta/NAVCAM)
The comet 67P/Churyumov-Gerasimenko with its two-lobed shape (Photo ESA/Rosetta/NAVCAM)

Two articles to be published in the journal “Astronomy & Astrophysics” describe various aspects of a research on the age of the comet 67P/Churyumov-Gerasimenko. Martin Jutzi and Willy Benz of the University of Bern, Switzerland, together with several colleagues conducted a series of computer simulations to study its two-lobed structure concluding that the collision that gave it its present shape hardly occurred over a billion years ago.

The mission of ESA’s Rosetta space probe was completed at the end of September 2016 but the huge amount of data collected on the comet 67P/Churyumov-Gerasimenko will still studied for many years. Among the many aspects investigated by scientists there was its out from the normal shape because it consists of two lobes connected by a neck. In September 2015 a study published in the journal “Nature” described the evidence that support the theory that its shape was due to the merger of two small comets.

That theory seems proven but scientists thought that the merger that created the comet 67P/Churyumov-Gerasimenko took place when the solar system was very young, about 4.5 billion years ago. At the time there was a huge amount of objects of various sizes including many comets that collided continuously so it seemed plausible that that collision had taken place during that chaotic period. Things could be different.

The first article describes the conclusions of the calculations of amount of energy needed to destroy a structure like that of the comet 67P/Churyumov-Gerasimenko’s nucleus. The neck is its weak point and can be broken even by a low-energy collision. According to the researchers, comets of that kind suffered various collisions over time so the one that, on the contrary, generated it must have occurred not in primordial times but in the last billion years.

In the second article the researchers studied the details of the formation of the comet 67P/Churyumov-Gerasimenko’s nucleus following a collision. In the simulations they had objects between 200 and 400 meters in diameter collide with a rotating egg-shaped body with a diameter of about 5 kilometers. The impact speed used in the simulations was between 200 and 400 m/s but the energy released was still much lower than that required to destroy the central body. The consequence was that the object was broken into two parts that had enough gravity for them to attract each other and merge in its present two-lobed shape.

According to current theories comets formed from primordial materials or at least as old as the solar system. This new research seems to contradict this theory but the analysis of the simulations results shows that it’s not like that. The explanation lies in the fact that the energy released in that kind of impact is not enough to radically modify their structure. The comet 67P/Churyumov-Gerasimenko’s nucleus remained porous and the original volatile materials didn’t get lost.

Only a few weeks ago, another research based on computer models presented at the European Planetary Science Congress (EPSC) concluded that the comet came into the inner solar system only during the past 10,000 years after traveling in the Kuiper Belt, beyond Neptune.

These researches are offering intriguing possibilities about the history of the comet 67P/Churyumov-Gerasimenko that give us some idea of the complexity of the solar system’s history. If the conclusions of these research will be confirmed those will be more surprises coming from a comet that in recent years proved to be a real treasure from the scientific point of view.

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