The asteroid Ryugu may be an extinct comet

Une image de Ryugu prise par Hayabusa 2. © Jaxa, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST

It’s been almost two centuries since we discovered that there are asteroids, but millennia for comets. However, it was not until the twentieth halfE Century Thus we begin to understand their nature and their origin. The revolution ofSpace science At the same time, it enabled us to observe them more closely, especially the great mission of ESA’s Geoto Probe approaching Halley’s Comet in 1986. In the investigation we know that the ESA is going to get better Rosetta Comet 67P / Tchourioumov-Guérassimenko.

In recent years, that has been the mission Hayabusa 2 provides not only taking the center of these small celestial bodies Close-up images of the asteroid (162173) RyuguAnd also because this mission made it possible to collect samples of it Asteroid Apollon Type C, dangerous, discovered in 1999. These samples have arrived on Earth and are still being analyzed.

Participated in the Hayabusa 2 mission in Cnes Ryugu. © Cnes

Three clues to the origin of Ryugu

Related first data Ryugu However, they were a little surprising, leading to the suggestion of some assumptions to take into account. The asteroid has the shape of a spinning top, which can be well explained if it adopts a form of equilibrium in response to its rapid rotation. All that remains is the figure of this rapid rotation.

To understand its equilibrium, it is necessary to know that Rഗgue found that it could be considered as a heap of debris composed of small rocks and objects. Solid A single monolith is held together by gravity rather than a rock. One way to explain this is to establish that fragments formed by a collision between two asteroids actually converge slowly due to their gravitational pull (the size of the Rugby is about 920 m).

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Another piece of data provided by the mission is that the tiny sky is incredibly rich Thing Organic.

(162173) A research team led by Hitoshi Miura reassembles all parts of the enigma of Ruge’s identity and origin in a completely different way. Nagoya City UniversityIn Japan, in an open access article The Astrophysical Journal Letters.

Planetologists have developed a new model that takes into account all of Ruge’s views, and concludes that it is a dead comet, which is what is left when it passes close to such an object in repeated orbit. In Sole Its collection of volatile substances is almost exhausted – mostly water ice.

A dirty snowball shrinks

The scene developed Equations Written by Hitoshi Miura of Okayama University in Japan and his colleagues Iso Nakamura and Tak Kunihiro, it is ideologically simple. If Ryugu was really a comet, we could compare it to a water ice cube whose chocolate chips melt on the surface and evaporate several times. The nuggets will residue and eventually concentrate and stick to the bottom of the bowl containing the initial mixture.

Formed beyond the orbit of Thursday In Protoplanetary disc About 4.5 billion years ago, a comet should have been so famous The “Dirty Snowball” model, long ago suggested by astronomer Fred Lawrence WhippleAcrylic blocks of different sizes, completely covered with ice.

As it evaporates, the size of the comet decreases, changing the moment of its inertia as a skater brings her hands together. Protection of Cinematic moment Lead her to own her Rotational speed Accelerate as its size decreases.

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The researchers’ model later attributed this shape of the spinning top to the calculated rotational speed. Way From Numerical simulations We understand why Rugu seems to be more carbonaceous than other asteroids studied from Earth using spectroscopy.

According to a statement from the University of Nagoya, along with the published scientific work, Spinning top and heap-shaped objects Carvings High organic content such as Ryugu and Bennu (mission objective) Osiris-Rex), Will be the comet-asteroid transit (CAT) objects. ” Cats are small comets that were once active comets but are now extinct and indistinguishable from asteroids. “Adding Hitoshi Miura Explains:” Because of their resemblance to comets and asteroids, CATs can provide new information about our solar system. .

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