First results of New Horizons weather in the Kuiper belt

For many at the Johns Hopkins Applied Physics Laboratory, January 1 of this year did not mean a New Year's celebration. It meant the first arrival of data from New Horizons' visit to a small Kuiper Belt object. But, as in his previous overview of Pluto, the probe was instructed to capture all possible data and send them back to Earth later. The complete set of all that New Horizons captured will only be available in one year. But with 10% of the total cache in hand, the researchers decided to have enough to do the first analysis of 2014 MU₆₉.

2014 MU₆₉ is thought to preserve the material as it has condensed in the early days of solar system formation. And all in the data of New Horizons suggests that it is exactly what he did. With the exception of a large crater named temporarily "Maryland" and the gentle collision that created its two-lobed structure, the object appears to have been largely spared by more than 4 billion dollars. Years of existence of the solar system.

The dawn of time

The Kuiper Belt is a sparse donut of small bodies located near the outer edges of the solar system. The bodies are mainly made up of icy materials, which for the most part would remain gases in the warm and inner regions of the solar system. Some, such as Pluto, are large enough and / or have a complex collision history, which can guarantee geological changes that alter the materials present during their formation.

But 2014 MU₆₉ is much smaller; Early estimates placed it less than 50 km in diameter. This suggests the possibility of preserving the materials present during its formation more than 4 billion years ago. Bodies like 2014 MU₆₉, collectively called planetesimals, also contributed to the formation of outer planets and larger objects in the Kuiper belt. So New Horizons 2014 study MU₆₉ provided a potential opportunity to better understand the conditions present at the beginning of the solar system, including those used to build larger bodies. But that would only be true if 2014 MU₆₉ has not been changed during his time in the solar system.

To study the subject, New Horizons came equipped with seven scientific instruments, including cameras, spectrometers to map the composition of its surface, and even particle and dust collectors to capture all materials 2014 MU₆₉ liberated in space. The closest approach to the spacecraft was about 3,500 km from 2014 onwards.₆₉, which allowed him to capture images that could solve 50-km (and in some cases, even smaller) entities.

Even as data was declining, the New Horizons team used them to create and refine models of the body surface. They checked if the imagery data was consistent with the troughs and curves of the model and modified the model if it was not. The results confirm those of the first images: 2014 MU₆₉ is actually two objects that snap gently until they connect via a strangled "neck" The researchers had dubbed 2014 MU₆₉ "Ultima Thule" and in this article they refer to the larger Ultima lobe and the smaller Thule.

Ultima is perhaps the largest of the two in most dimensions, but it is also flattened. This gives it the appearance of a crepe thick about 20 km but only 7 km. Thule is a little more rounded, with dimensions varying between 10 and 14 kilometers, but it also houses the most obvious impact crater on the body. This crater has been dubbed "Maryland", and other surface elements have been labeled with the names of the states where the New Horizons team is working. (All of these names are temporary and will almost certainly be replaced.)

A silent place

Nothing indicates that the two lobes were reunited violently. Both lobes seem to have retained their original forms because there is no sign of compression or fracture, and their orientation suggests that they have spent enough time near one. on the other to lock in tide before merging. The New Horizons team suggests that the two were reunited at speeds similar to those you expected due to their mutual gravitational pull (which, given their size, is small). However, Ultima and Thule appear to be formed somewhat separately, as both lobes can be distinguished according to the color of their surface materials.

2014 MU₆₉Like the other objects in the Kuiper belt, it is reddish in color; New Horizons confirmed that the reddish hue continued in the near infrared. The brightest areas of the surface tend to be at the edge of slopes, as in the Maryland Crater and the neck between the lobes. The researchers suggest that this could be the result of the accumulation of loose materials at the base of a slope.

Although the instruments detected many traces of ice, there was no indication of the nitrogen and methane ice that prevailed on Pluto. The temperature estimates suggest that the whole body should have reached a balance of about 42K, which is hot enough to cause the evaporation of these substances; the orbit of 2014 MU₆₉ Also guarantees that certain areas will spend decades in the sunlight, causing localized heating that should improve this process.

However, there was no evidence that materials were rising from the surface, suggesting that the ice was stable and other volatile substances had already disappeared. While this may be due to the limitations of New Horizons instruments, researchers estimate that at most, 2014₆₉ would have lost about 10 cm of material from its surface during its entire history.

Static

Finally, there is a notable absence of obvious impacts outside the great Maryland crater. In addition, there are pits that are about 1 km in diameter, but they are not clearly the product of impacts. And there is absolutely nothing in the size range between the two.

Overall, 2014 MU₆₉ It looks exactly like what we were hoping for: a world that has undergone major changes immediately after its formation, but which has since become static, has preserved its state, as it was billions of years ago. Hopefully more details about this state are stored in New Horizons. Because we are not likely to send something back to 2014 MU₆₉ very soon.

Science, 2019. DOI: 10.1126 / science.aaw9771 (About DOIs).