Scientists have published a summary of the results of the first phase of the study of the object 2014 MU69, also known as Ultima Thule. This is the first medium-sized Kuiper belt body near which a research probe flew. The researchers managed to collect data on the presence of satellites and rings, measure the optical and geological parameters of the body, as well as estimate its age and put forward a theory of its origin. The results are published in the journal Science.
Beyond the orbit of Neptune, at a distance of 30 to 55 astronomical units from the Sun, lies the Kuiper belt. This remote region of the solar system is inhabited by many objects, the most famous of which is Pluto. The study of bodies located in this region is of separate interest for astronomy, since local objects have never been heated by the radiation of a luminary to high temperatures and therefore retain many of the properties of the original matter from which the solar system was formed.
The first scientific apparatus created to study objects in the Kuiper belt was the New Horizons probe. Its main target was Pluto, which the spacecraft flew past in the summer of 2015. The next target was a small object (486958) 2014 MU69, called Ultima Thule. The passage next to it took place on January 1, 2019, but due to the large volume of collected information and the remoteness of the object, the transfer of all data will take many more months and should be completed only by mid-2020.
However, already received on Earth and processed data, which are about one tenth of the total volume, allowed astronomers to draw a number of conclusions about the studied object. MU69 turned out to be a cool classical body of the Kuiper belt, that is, it belongs to the class of objects with stable orbits in shape close to a circle and a small inclination to the ecliptic plane. This suggests a high likelihood of no major disturbances since the formation of the solar system and the original formation of Ultima Thule near its current position about 4.5 billion years ago.
Ultima Thule turned out to be about 30 kilometers in size, and in shape it was similar to a snowman cobbled together from two thick disks. It did not have any satellites, signs of a cometary tail, atmosphere or surrounding dust clouds. The bipartite form speaks of the formation, as a result of non-catastrophic cohesion, of a pair of initially separate bodies, which could have formed next to each other and revolved around a common center of mass in the distant past. The similar composition of the parts is also an argument in favor of forming from a single cloud.
The surface of MU69 has a low albedo, that is, it reflects little light and is therefore dark; reflectivity ranges from 5 to 12 percent. The most striking parts are the “neck”, as well as two spots inside the crater-like depression. Despite fluctuations in albedo, the body color is uniformly reddish. Spectral studies have revealed absorption lines of water and methanol.
Body temperature is about 42 Kelvin, with daily and seasonal fluctuations affecting only the outermost layers. At this temperature, volatile compounds, such as carbon monoxide, methane and molecular nitrogen, not trapped in the cavities of other substances, should have evaporated during the lifetime of the solar system.
In terms of geology, there are several regions with slightly different properties, but no noticeable variations in color and surface composition were found. The authors note a low density of noticeable craters, which indicates a small number of bodies about a kilometer in size in the Kuiper belt, as well as a lower collision frequency than expected in an equilibrium population.
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Timur Keshelava