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After death, the brain is one of the first organs to begin the deterioration process. Its cells start to self-digest, resulting in the loss of its characteristic shape within a few hours and turning into a paste within a few days.

However, this is not a universal rule. Archaeologists have already located ancient brains that remained almost intact, even when the rest of the body had decomposed. Previously, this phenomenon was considered extremely rare and a mystery to archaeology.

This perception changed in 2024, when a study conducted by Oxford University, led by researcher Alexandra Morton-Hayward, aimed to quantify the frequency of this event. After analyzing the largest volume of scientific literature on the subject, the team identified over 4,000 records of preserved human brains, distributed across six continents and various cultures, from members of the Ancient Egyptian royalty to Arctic explorers. This number is approximately twenty times higher than previously assumed.

Although part of these cases was linked to already known preservation methods, such as mummification and freezing, about a third of the records did not have such conditions; in these cases, the brain was the only preserved bodily structure.

Scientists at Oxford University have been investigating this enigma, which they have nicknamed the 'brain preservation paradox.' They currently believe they have found an explanation: preservation may be the result of a chemical process that occurs during decomposition under certain environmental conditions, indicating that it is not an extreme rarity.

The findings were detailed in an article published in June in the scientific journal Journal of Proteome Research. The researchers noted that most preserved brains were found in soils with low oxygen availability and high humidity, such as river and lake banks. Based on this, they formulated the hypothesis that these environments alter the normal process of protein decomposition in the brain.

To validate this theory, the team conducted a series of experiments, burying rats in four containers with different combinations of humidity and oxygen. Over six months, the researchers monitored the state of brain decomposition. Initially, protein degradation followed a similar pattern in all groups. However, after a few weeks, significant differences emerged.

In environments rich in oxygen, free radicals—highly reactive molecules—accelerated the deterioration of brain proteins. In contrast, in humid, low-oxygen locations, these same free radicals promoted the formation of cross-links between proteins, giving them greater resistance and halting the degradation of brain tissue. Brain proteins cease digestion and stabilize.

The authors state that 'degradation is not the opposite of preservation. Under specific chemical restrictions, the same oxidative reactions that drive molecular destruction can also generate molecular stability.'

The researchers now plan to deepen the investigation of this mechanism. In addition to helping archaeologists understand why certain brains persist for millennia, this phenomenon may offer valuable information for medical research related to protein stability and neurodegenerative diseases.

Celestial bodies known as rogue planets, which travel through space without orbiting a star, have always been studied by astronomy. However, there was uncertainty about what happens to the moons of these planets when they are ejected from their original systems. A new study sought to clarify this issue by conducting thousands of stellar encounter simulations.

Scientists from the Leiden Observatory, located in the Netherlands, examined approximately 34 thousand scenarios where a star passes near a planetary system, modifying its gravitational dynamics. The findings, published in the arXiv preprint repository, demonstrate that the survival of a moon is fundamentally linked to the distance at which it orbits its planet. Additionally, the characteristics of these orbits can help astronomers understand how the ejection of these systems occurred.

This work was conducted by Yannick Badoux and Simon Portegies Zwart, monitoring the fate of planets and their respective moons during close approaches with other stars. According to the simulations, the determining factor is the so-called Hill radius, which defines the area around a planet where its gravitational attraction is stronger than the influence of the host star. It is within this limit that a moon can maintain its orbit.

The researchers found that moons located up to about 40% of the Hill radius tend to follow the planet even after it is ejected from the system. Conversely, those located beyond this limit quickly lose their gravitational bond. From approximately 50% of the Hill radius, the separation between the planet and the moon becomes virtually inevitable.

The scientists suggest that this behavioral pattern may help distinguish rogue planets ejected after passing another star from those ejected by gravitational interactions with other planets, since each process tends to leave distinct signatures on the orbits of the surviving moons.

The conclusions obtained were applied to a well-known example from our own Solar System. The study points out that if Jupiter were removed from the Solar System by a nearby passing star, the moons Io, Europa, Ganymede, and Callisto would continue to orbit the gas giant. This is because these four moons are very close to the planet, occupying less than 1% of Jupiter's Hill radius.

The authors emphasize that the gravitational encounter leaves different marks on the remaining moons. Those that remain in closer orbits tend to maintain nearly circular trajectories, while those that barely escape exhibit more inclined and elongated orbits.

Furthermore, the simulations indicate that in approximately 87% of ejection events, the distance between the planet and the moon varies by less than 10%. The researchers believe that this characteristic allows astronomers to reconstruct the history of these systems just by observing the moons' orbits.

The team also used the model on an object already identified through the gravitational microlensing technique, cataloged as MOA-2011-BLG-262L. This object could be a rogue planet accompanied by a moon smaller than Earth's, although current data still allow for other interpretations.

If this hypothesis is confirmed, the simulations suggest that the system probably originated between 1.3 and 5.9 astronomical units from its star, with a slight preference for about 5.2 astronomical units, a distance comparable to that separating Jupiter from the Sun.

The study also highlights a notable consequence of these moons remaining with their planets. Certain moons can generate internal heat due to the gravitational forces exerted by the planet they orbit, regardless of starlight. Europa, for example, has a subsurface ocean whose existence is attributed to this heating. Thus, if a planet is expelled taking its moons, this heating mechanism can continue even in interstellar space, keeping these satellites warm without the need for a star.