Mercury, with a size just one-third that of Earth, is currently the smallest planet in the Solar System. However, in the past, Mercury and Earth were of similar size until a significant event occurred.
As the planet closest to the Sun, Mercury has long attracted the interest of astronomers due to its extreme temperature fluctuations (ranging from -173 degrees Celsius at night to 427 degrees Celsius during the day) and its surface, which is riddled with impact craters.
Close-up of Mercury’s surface. (Photo: NASA).
According to Interesting Engineering, studying Mercury presents numerous challenges. Because this planet is located so close to the Sun, spacecraft must exert tremendous effort to counteract the gravity of the central star when approaching Mercury.
This means that spacecraft need to consume a massive amount of fuel to avoid the disastrous fate of being drawn into the Sun.
Despite these significant challenges, the National Aeronautics and Space Administration (NASA) has successfully conducted two missions that approached Mercury closely enough to map the planet.
The results show that, contrary to its small appearance, Mercury possesses a massive core compared to its mantle, while its crust is extremely thin.
Mercury also has an unusually high density of thorium, an element that should have evaporated due to the planet’s intense heat. Finally, similar to Earth, Mercury possesses a magnetic field, suggesting that Mercury’s internal activity may be remarkably similar to that of Earth.
Gathering this information, planetary researcher Nicola Mari from the University of Pavia (Italy) and his colleagues sought to compare the structure of Mercury with that of Earth. They discovered that these two planets are quite similar, implying that in the past, their sizes may have been virtually identical.
To explain Mercury’s small size today, researchers propose that Mercury once collided with some external force, resulting in its crust being stripped away and leaving the state we observe today.
The European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) have collaborated on the BepiColombo mission, launched in 2021, with the goal of exploring Mercury, and experts are eagerly awaiting results from this mission.
