Asteroid Ryugu may be an extinct comet

About two centuries have passed since we discovered the existence of asteroids, and comets – millennia. However, only in the second half of the twentieth well as century, so that we begin to understand their nature and origin. Revolutionastronautics even allowed us to observe them more closely at that time, especially the spectacular mission The ESA Giotto probe approaching Halley’s comet in 1986.. I’ESAas we know, was going to do much better with the probe Rosetta and comet 67P/Churyumov-Gerasimenko.

In recent years, the Hayabusa-2 mission has taken center stage in the study of these small celestial bodies, providing not only close-up images of asteroid (162173) Ryugubut also because this mission made it possible to collect samples of this asteroid Apollo type C, potentially dangerous, discovered in 1999. These samples arrived on Earth and are still being analyzed..

Knes participated in the Hayabusa 2 mission to Ryugu. © Knes

Three clues to the origin of Ryugu

However, the first Ryugu data was a bit unexpected and led to some hypotheses to explain it. The asteroid does indeed have a tip shape, which is well explained if it took on an equilibrium shape in response to its own rapid rotation. It only remained to explain this rapid rotation.

To also understand its form of balance, it is necessary to know that it has been found that Ryugu can be seen as a pile of rubble, composed of small pieces of stone and materials. solid agglutinated the force of gravity not a single monolithic rock. One way to explain this is to postulate that these are actually fragments formed by the collision of two asteroids, which then had to slowly join under the influence of their own gravity (the size of Ryugu is approximately 920 meters).

According to other data provided by the mission, the small celestial body is surprisingly rich in organic matter.

All of these puzzle pieces about Ryugu’s identity and origins (162173) have been put together in an entirely new way by a research team led by Hitoshi Miura from Nagoya City Universityin Japan, in an open access article in Letters from an astrophysical journal.

Planetologists have built a new model that better explains all of Ryugu’s observations, and have come to the astonishing conclusion that it is a dead comet, that is, what could be left of such an object on Earth. orbit periodic, when its repeated passages close to the Sun have almost exhausted the supply of volatiles – mainly water ice.

Dirty snowball

Script developed with equations Hitoshi Miura and his colleagues Eizo Nakamura and Tak Kunihiro of Okayama University, Japan are conceptually simple. If Ryugu really was a comet, then we can compare it to water ice with chocolate chips melting on the surface and evaporating several times. The nuggets will settle and eventually concentrate and collect at the bottom of the container containing the original mixture.

Formed outside the orbit Jupiter in protoplanetary disk Originally about 4.5 billion years ago, the comet must have been so famous the so-called “dirty snowball” model, long proposed by astronomer Fred Lawrence Whipple.intergrown blocks of various sizes with ice encapsulating everything.

Evaporating, the comet decreases in size, which changes its momentum.inertia as in the case of a figure skater bringing her hands together. Preservation cinematic moment lead her to her rotational speed accelerate as its size decreases.

The researchers’ model then explains this top shape caused by the calculated rotation speed. across from numerical simulation and we also understand why, since it was originally a comet formed in cold regions rich in volatile organic matter, Ryugu appears to be much more carbonaceous than other asteroids studied from Earth using spectroscopy.

According to a statement from Nagoya University accompanying a published paper, the top and pile objects rubble with a high organic content, such as Ryugu and Bennu (mission target Osiris Rex) will be comet-asteroid (CAT) transition objects. ” CATs are small objects that were once active comets but have become extinct and are apparently indistinguishable from asteroids. “Hitoshi Miura explains, who adds:” because of their similarities to comets and asteroids, CATs could provide new information about our solar system. “.

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