Mercury, the smallest planet in the Solar System, is showing signs of more pronounced shrinkage than predicted, according to a new study published in the journal Geophysical Research Letters this Thursday (10th).
Although it was known that the planet's interior has been decreasing since its formation 4.5 billion years ago due to cooling, the surprise lies in the intensity of this shrinkage, which exceeded researchers' expectations.
On the planet, indications of this shrinkage manifest through elevations and ridges known as shortening structures, distributed across its surface. As time progresses and the planet shrinks, new ridges emerge; the article demonstrates that many of these structures have remained hidden until now, buried by craters and debris, suggesting a greater shrinkage than previously believed.
The difficulty in estimating the exact size of the planet is due to the inherent challenges of its research. Since it is the celestial body closest to the Sun, sending space probes is complicated, and no mission has managed to investigate Mercury's subsurface to date. Furthermore, intense sunlight prevents effective observation of the planet from Earth.
Therefore, scientists rely on data obtained by remote satellites to gain insight into the internal layers. In this specific case, the data used was provided by the Messenger space probe.
This robotic spacecraft was launched in August 2004, reached Mercury in March 2011, and completed 4,105 orbits before running out of fuel and colliding with the surface in 2015. However, during its more than four years of operation, Messenger managed to collect a vast amount of information.
It was from the dataset gathered by Messenger that researchers arrived at this new assessment of Mercury's shrinkage. A team led by Gaku Nishiyama from the German Aerospace Center's Space Research Institute (DLR) cross-referenced two pre-existing maps of the planet: one detailing the distribution of ridges and scarps created by contraction, and another mapping the surface roughness. This second map was constructed from laser measurements and images captured by the probe from different angles, allowing for a three-dimensional reconstruction of the terrain. It was the comparison between these two maps that revealed a previously unnoticed pattern.
The analysis focused on surface roughness, which is mainly caused by impact craters and the debris scattered by them. This roughness can cover the ridges and scarps resulting from contraction, making them difficult to identify. Considering this factor, researchers calculate that Mercury has likely shrunk between 10% and 30% more than previously assumed.
The authors of the study themselves warn that these values may still be below reality, given that the available surface data may be incomplete.
The cause of this phenomenon is linked to the planet's origin. Like all rocky planets in the Solar System, Mercury formed 4.5 billion years ago during a period of great cosmic upheaval, when rocks and asteroids collided and subsequently merged. This impact process generated intense heat, which the planet has been losing ever since.
Currently, Mercury boasts the most extreme temperatures in the Solar System, with thermal variations ranging from -184°C to 427°C, as it lacks an atmosphere capable of regulating heat. As its interior cools, the planet develops geological grooves in the form of scarps and ridges, serving as indicators for researchers to identify its shrinkage process.
With a diameter of approximately 4,879 kilometers, Mercury is the smallest planet in the Solar System. It is only one-third the size of Earth and is so small that some moons, such as Jupiter's Ganymede and Saturn's Titan, are larger than it.
