Someone took rocks from Mercury and left them in Cyprus?
In the search for how our solar system formed, various missions with different telescopes take photos of the surfaces of planets if they can’t land on them. These photos, in various filters or in error analysis, can reveal to us the composition of these planets and perhaps how they were formed, as well as how our own planet was formed.
Scientists have found that the geochemical composition of the planet Mercury is very similar to that of rocky areas of the Troodos Mountains in Cyprus!
What happened, though? The Mercurians, extraterrestrial beings, were fascinated by the island of Aphrodite and came to leave us… rocks?
Let’s start from the beginning. Mercury is a planet in our solar system that… exhibits many extremes! It is the closest planet to the Sun, making its study difficult for many reasons. Initially, it is very small, with a volume just slightly larger than that of the Moon. Also, being so close to the Sun, any mission approaching it is easily endangered by the Sun itself due to gravity (Sun: “my rocket is mine, you won’t take it Mercury!”) and even if it reaches close by, the mission might not withstand the high temperatures of our star (Sun: “and if it reaches, I’ll burn it!”). And yet, with the help of neighboring planets (“together we can do it!”) and maneuvers around them so that the spacecraft can slow down before getting lost in the gravitational field of the Sun, the ESA is attempting to study it better in its latest mission.
However, there are previous studies that give us some clues about how this planet is. The Mariner 10 and Messenger missions managed to get close enough to map its surface. And what did they see there?! Volcanic craters, its core, its magnetic field, and more!
Planets that are close to the Sun are mainly rocky planets with primarily a small core, a mantle of magma, and a hard crust (see volcanoes on Earth). This happens for Earth, Mars, and Venus, but Mercury came to change that. Mercury’s crust appears to be surprisingly thin, while its core is unexpectedly massive compared to the mantle. Furthermore, its composition has excessively high levels of thorium, an element found in rocks, stones, soil, water, plants, and animals. It is radioactive and evaporates with temperature. Its content of this element is close to that of Mars.
What does this tell us? Here’s where it gets tricky. The main assumption is that the planet Mercury wasn’t always so small. Researching something like this would be easy if we could dig into it and take samples, but since nothing has managed to land there yet… scientists are looking elsewhere, at analogous rocks that have similar composition.
Initially, some meteorites with similar composition were analogous. This means two things. Either these meteorites were part of the planet Mercury, and as various collisions occurred during the birth of our planetary system, they were a result of such a collision, or they were born in the same region as Mercury long ago, after the solar system was forming and evolving, and the meteorites fell to Earth. The second theory generally prevails for such meteorites, so scientists and Mario, a planetary geologist in Italy, decided to investigate it further in analogous geochemical analogues of our own planet. And his search sent him to the mountains of Cyprus. Cyprus, or rather Venus, was born in the depths of the sea 90 million years ago and emerged on land, and the relief of its mountains resembles ocean depths. In these mountains, after exhaustive search, Mario found what he was looking for, pieces of lava called boninites. These are part of the mantle at its depth and in Cyprus, with the movement of the tectonic plates they moved to the surface. He analyzed them with his team and found their composition to be a perfect match for Mercury’s chemical analysis! This does not mean that Mercury left us its composition though… This is an indication that such rocks with this chemical composition are born in a thick mantle (like Earth’s) and this is an indication that Mercury once had a thick mantle like that of Earth and some violent event took him away!
Such studies are just a small part in the creation of planets and the positions and orbits they acquire around a star. The BepiColombo mission aims to better investigate the planet Mercury, with its final approach in 2025 splitting into two craft, one to measure its magnetic field and one to measure its surface and interior composition. Corresponding analogs for the rest of the planets are found elsewhere on Earth, and their composition and origin give us clues about the mantle and crust of both Earth and the planets, in an effort to better understand our creation and existence around the helium.
Article is based on [1] BBC article https://www.bbc.com/future/article/20240410-mercury-the-solar-systems-smallest-planet-may-once-have-been-as-large-as-earth
and [2] in the scientific publication Mari N., Eggers G.~L., Filiberto J., Carli C., Pratesi G., Alvaro M., D’Incecco P., et al., 2023, P\&SS, 236, 105764. doi:10.1016/j.pss.2023.105764 https://ui.adsabs.harvard.edu/abs/2023P%26SS..23605764M/abstract