Ice bombs; that is how scientists now describe icy space rocks in the Kuiper Belt. However, recent research now shows that some ‘ice bombs’ are likely to contain valuable information.
Kuiper Belt Object 486958 Arrokoth is not just any space rock; the object consists of two unequal ‘discs’ that are attached to each other, which scientists say makes the object resemble a primitive snowman. This comparison now appears to go a lot further than previously thought. Researchers have recently discovered that the snowman actually contains ice. This ice is very special because it probably comes from the era when the space rock was formed – billions of years ago. As a result, the snowman suddenly turns out to be a gold mine for science: the ice in these space rocks is often ice made from substances that evaporate quickly. Scientist Sam Birch contributed to the research. He says: “Many scientists were convinced that this type of ice had long since ceased to exist. We will come back to that now; we are confident they can still be found.” The research has been published in the journal Icarus.
Sublimation
For the research, Birch’s team looked at Arrokoth, an object in the Kuiper Belt. This object was viewed closely for the first time when the space probe New Horizons flew by. It was determined that the space rock indeed appears to have a kind of spongy structure, as is often the case with these types of objects. However, no CO gas was spotted on the outside, which the scientists say is extremely remarkable. Ultimately, this turned out to be due to a domino effect that takes place in the space rock itself. To properly understand the explanation of this, it is important to first point out that ‘ice’ does not only mean ‘water ice’. There are many more substances that turn into a kind of ice when they become very cold, such as the gas carbon monoxide (CO). However, this gas has a boiling point of -191.47 degrees Celsius, which in practice means that CO ice will immediately evaporate into gas when it becomes warmer – a process also called ‘sublimation’.
Now Birch’s explanation regarding the cause of the domino effect: “Essentially we have discovered that it is so cold inside Arrokoth that the CO ice present can only sublimate when the cold CO gas already present first is absorbed by the spongy structure. However, there is a problem here: the gas present can only disappear when more ice sublimates. This creates a domino effect: it becomes colder in Arrokoth, resulting in less ice sublimating. Because less ice sublimates, the cold gas present cannot escape as well, which only makes it colder in Arrokoth. Eventually it gets so cold that the whole process comes to a standstill. The result is an object that is full of gas that can hardly escape.” This is why these objects are now described as ‘ice bombs’; As they get closer to the sun, the gas inside the object can suddenly come under pressure, causing them to explode violently.
Scientific treasures
The results of the study are particularly significant because the CO ice (and gas) in Arrokoth has been self-sustaining for billions of years. Bircht explains: “Our research has shown that these primitive types of ice can be locked up in KBOs. It is therefore quite possible that many primitive substances (from billions of years ago, ed.) are ultimately locked up in objects located on the outside of our solar system.”
Fellow scientist and team member Orkan Umurhan concludes: “During this research, we fixed a bug in the physical model that scientists often use for old and cold objects. As a result, this research could ultimately change the theories surrounding the formation of comets. Not only that; It is also quite possible that scientists will now think differently about what exactly happens in such a space rock.”
