CNN
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Researchers suspect that two metstones found in the Sahara in 2023 originally came from Mercury, making it the first identified fragment of the innermost planet of the solar system.
The most studied and most mysterious mercury of the rocky planets of solar systems is so close to the sun, it is difficult to explore even with probes. So far, only two non-white-stricken spaceships have visited. Mariner 10 was released in 1973, and Messenger was released in 2004. The third Bepicolombo is in the middle and in the middle to orbit around the planet in the second half of 2026.
Scientists have little knowledge of Mercury’s geology and composition, and have been unable to study fragments of planets that landed on Earth as erosion material. In contrast, the Meteorical Society’s database, an organization that catalogs all known metstones, has over 1,100 known samples from the Moon and Mars.
These 1,100 metstones come from when fragments were cast from the surface of the moon and Mars during an asteroid collision, before heading to Earth after traveling through space.
Not all planets are likely to eject fragments towards Earth during their collision. Venus is closer to us than Mars, but its large gravitational pull and thick atmosphere can prevent the firing of impact fragments. However, some astronomers believe that mercury should be able to produce meteors.
“Based on the amount of Lunar and Martian metstones, there should be around 10 mercury metstones, according to dynamic modelling,” says Ben Reider Stokes, a postdoctoral researcher of achondrite metstones at the UK Open University and author of a study of the Sahara Meteor study, published in the Journal of Ikuars in June.
“But mercury is much closer to the sun, so anything that has been kicked out of mercury needs to escape the gravity of the sun to reach us. It’s dynamically possible and it’s just that difficult. No one has identified the metstones from mercury yet,” he said.
Two met stones discovered in 2023 – named Northwest Africa 15915 (NWA 15915) and Ksar Ghilane 022 (kg 022), according to Rider-Stokes, a great advancement of scientists’ understanding will greatly advance. However, he and his co-authors are the first to warn of some contradictions in matching those space rocks with what scientists know about Mercury.
The biggest is that the fragments appear to have formed about 500 million years before the mercury itself. However, according to Rider-Stokes, this finding may be based on inaccurate estimates, and a conclusive assessment is unlikely. “Until you return the material from the mercury or visit the surface,” he said.
However, there are several compositional clues that suggest that metstones may have connections to the planet closest to the Sun.
This is not the first time known metstones have been linked to mercury. The previous best candidate based on the level of interest that peaked astronomers was a fragment called Northwest Africa (NWA) 7325, reportedly found in southern Morocco in early 2012.
Rider Stokes said it was the first metstone that could be associated with mercury. “It attracted a lot of attention. Many people were very excited about it.” However, further analysis showed the richness of chromium that opposed the predicted surface composition of Mercury.
More recently, astronomers have suggested that from a small metstone that landed in over in France in 1836, a class of meteorites, called orblites, may come from the subsurface layer of Mercury. However, these metstones are not chemically compatible with what astronomers know about the planet’s surface, Rider Stokes said. “That’s what’s very exciting about the samples we’ve studied. They have the optimal chemistry to represent mercury,” he said.
Most of what is known about Mercury’s surface and composition comes from NASA’s messenger probes, which evaluated the composition of the planet’s crust from orbit. Both metstones from studies that Rider Stokes analyzed with several instruments, including electron microscopes, contain olivine and pyroxene.
New analysis also reveals a total iron deficiency in the space rock samples. This is consistent with scientists’ assumptions regarding the planet’s surface. However, metstone only contained trace amounts of agricultural quantities, minerals thought to govern the surface of mercury.
However, the biggest point of uncertainty remains the age of the metstone. “They’re about 4.5 billion years old,” said Ryder Stokes.
However, he said he believes that this inconsistency is not sufficient to rule out Mercurian’s origins, as the reliability of the messenger data, which is also used to estimate the era of Mercury’s surface layer.
“These estimates may not be entirely accurate as they are based on impact crater models rather than absolute age dating,” Rider Stokes said. “This does not mean that these samples are not suitable analogs for regions on the surface of mercury or for early mercury crusts that are invisible to modern surfaces of mercury.”
With more modern instruments now available, Bepicolombo, a study by the European Space Agency, which will begin studying mercury in early 2027, may be able to answer long-standing questions about the planet. And whether it has water or not.
The confirmed arrival of other planetary bodies will help astronomers understand the nature of early solar system components, Rider Stokes said. And it is especially important to identify mercury fragments.
Sean Solomon, the lead researcher of NASA’s messenger mission to Mercury, said in an email that he believes that the two metstones described in a recent paper are likely not derived from Mercury. Solomon, a part-time senior research scientist at Columbia University in New York City, was not involved in the study.
The main reason Solomon cited for his suspicion is that the meteor formed much earlier than the best estimate of the age of the rocks currently on Mercury’s surface. However, he said he still thinks the sample is research worth.
“Nevertheless, the two metstones share many geochemical properties with mercury surface materials with little or no iron, and the existence of sulfur-rich minerals,” he added. “These chemical properties are interpreted to indicate that mercury formed from the precursor material has been reduced much more chemically than the ones that formed Earth and other inner planets. The remains of the mercury precursor material may still remain somewhere in the inner solar system.
Solomon also said it is difficult to persuade the planetary science community that there are samples from Mars in the Meteorite collection, and it is difficult to accurately match the data and chemistry of Mars’ surfaces taken by Viking Probes, as well as to persuade researchers to consider the details. Moon metstones added that after the existence of Mars metstones was demonstrated in the 1980s, it was not widely recognized as being in the Metstone collection, despite the Apollo and Luna missions returning rich samples of the lunar material over a decade ago.
Once the samples were confirmed to be from the planet’s body, Solomon said that the timing of major geological processes, the history of internal melting of the body, and orbital spacecraft on the formation of the planet and the clues of early solar system processes can provide important information that is not available from remote sensing.
Rider-Stokes will continue discussions on these metstones at the Meteorical Society’s annual meeting this week in Perth. “I will discuss my findings with other scholars around the world,” he said. “At this point, we cannot clearly demonstrate that these are not mercury, so until we do that, I think these samples will remain the main topic of discussion across the planetary science community.”
