Flyby's data reveal a confusing amount of missing objects at the periphery of the solar system


The Kuiper Belt is found in the dimly lit spaces of our solar system beyond the orbit of Neptune. This region is about 35 to 50 times farther from the sun than the Earth, populated by icy bodies so little distributed that they have never had the chance to strike and blend into objects the size of A planet.

Pluto is the largest we know, but only. And over the past two decades, telescope surveys have uncovered a few thousand more, whose size does not exceed a few tens of kilometers.

The problem is that most objects of this size or smaller size are too small to be spotted by telescopes. It will be difficult to determine the number of tiny but invisible bodies in the Kuiper Belt. Now a new article, published in Science, used an ingenious method to help us discover.

This is important because scientists believe that objects in the Kuiper Belt are survivors of the birth of the solar system and develop from a primordial cloud of dust and gas. This means that their size distribution could tell us a lot about how the material from which the planets were developed was assembled.

Count craters

Instead of directly counting small objects from the Kuiper belt, the researchers behind the new study counted the craters created by the random sample of objects that impacted Pluto's surfaces and its largest moon, Charon.

There, craters 13 kilometers (8 miles) would have been created by objects of a size between 1 and 2 kilometers (0.6 to 1.2 miles).

This is already well below the telescopic detection limit for the Kuiper Belt objects themselves, but NASA's New Horizons mission flyby images in 2015 allow mapping of craters to be found. barely 1.4 kilometers.

These must have been caused by objects not exceeding 100 meters from the Kuiper belt.

record 20190225 26171 1u9e0wThe crater surface of Vulcan Planitia de Charon. (NASA / Johns Hopkins University APL / SRI / K. Singer)

The analysis of the researchers shows that, for craters of 13 km or more, both on Pluto and Charon, the frequency of impacts of different sizes seems to correspond to that expected from the known size distribution for the objects of the Kuiper belt.

However, for small craters, abundance decreases considerably, as does the abundance of Kuiper Belt objects capable of forming these craters.

The same thing does not happen for well-documented asteroids that collide with bodies in the Jupiter, Mars and Earth region, nor with the theoretical models.

The interpretation of the most craterized terrain has led researchers to rule out small craters being erased by geological resurfacing such as cryovolcanic activity (eruptions of icy fluids) over the last four billion years.

This reinforces the conclusion that the small craters have never been realized in the expected numbers. So there must be a mysterious corresponding deficit of objects in the Kuiper belt of less than 1 to 2 kilometers or so.

Blorping and thrilling

When researchers, led by Kelsi Singer of the Southwest Research Institute in Boulder, Colorado, wrote their paper, no one had seen a small Kuiper belt object in detail yet.

However, New Horizons recently flew over a 30 km long object known as the 2014 MU₆₉ (dubbed the most controversial "Ultima Thule") on January 1st and has probably transmitted the best images we will have.

Sometimes described as "snowman-shaped", it is a two-lobed "binary contact" formed almost certainly by the fusion of two round objects that occurred so slowly. and so gently that none of the components has been distorted during the process.

But what happened before that? If you look at the larger of the two lobes, in particular, you can distinguish what looks like traces of components that have merged with enough force to form a rough sphere, but with insufficient violence to break each other.

record 20190225 26181 17snz3tKuiper belt object 2014 MU₆₉. NASA / APL / SRI Johns Hopkins, National Observatory of Optical Astronomy)

These ideas inspired new original terms. "Blorping" refers to the material collision fusion to assemble each of the lobes, and "flomping" describes the approximation when two lobes meet without causing deformation.

More importantly, this could provide insight into the processes that deprived the Kuiper Belt of smaller objects that would otherwise have had an impact on the creation of small craters on Pluto and Charon.

The relative lack of small objects in the Kuiper belt can be explained by the fact that, instead of separating in the event of a collision, they have tended to splinter – eventually becoming objects like 2014 MU₆₉ .

If this is correct, when we try to count them, we see a record of growth rather than fragmentation by collision.

The further you get from the sun, the slower the orbital speed. Collisions are expected to be less violent in the Kuiper belt than in the inner solar system.

Nevertheless, even in this case, a "blorp" event that melts two clumps rather than separates them probably requires that the ice-creams that make up the bulk of their substance be much less brittle and more mellow than what we do. expected.

This is crucial information because these lumps are made from the raw material from which the solar system was formed, shedding important light on its evolution.

David Rothery, Professor of Global Geosciences, The Open University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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