University of São Paulo: Study of meteorites is essential for understanding space phenomena

THEThe fall of a meteorite in Minas Gerais, in mid-January, generated discussions about the importance of conserving the fragment. In images that went viral on social media, residents of the region displayed alleged parts of the meteorite in their hands and washed the space rock with soap and water.

“Meteorite” is the nomenclature used to describe the rock fragments that manage to reach the Earth’s surface. According to Gabriel Gonçalves, a doctoral student in astrobiochemistry at the Institute of Chemistry (IQ) at USP, the eventual entry of items into the Earth’s atmosphere happens when asteroids, large celestial bodies orbiting the sun, cross the planet’s orbit. “The body falls very quickly and compresses the air in front of it, which then heats up and glows, like an incandescent light bulb,” says the researcher. The band of light visible in the sky during the fall is called a meteor or, popularly, a shooting star.

Out of curiosity, Gonçalves also explains the definition of comets: “They are rocky bodies like asteroids, but they come from more distant regions of the Solar System and release many vapors, responsible for creating a luminous tail. Comets are visible in the sky for several days, while meteors are visible for just a few seconds.”

Meteorites also differ from one another. The most common are the undifferentiated ones, also known as chondrites, which make up about 85% of the celestial artifacts found on the surface. “You can recognize them relatively easily”, says Gaspar Rojas, a professor at the Institute of Geosciences (IGc) at USP. Metallic meteorites, another important group, can also be recognized by laypeople with some ease. The difficulty arises in identifying a third group, the differentiated meteorites, which are extremely similar to native rocks of our planet.

How to identify them?
To confirm that a fragment found is a meteorite, the indication is to send photos or samples of the rock to specialized institutions, such as the IGc itself. However, some specific features of extraterrestrial bodies can be observed even at home, and the professor at the Institute of Geosciences, Lucelene Martins, indicates steps for testing the fragments.

“Do you have the rock in your hand? Do the magnet test. In general, metallic meteorites and chondrites are well attracted to it, due to the presence of metallic iron. It is very rare to find it on Earth, but in meteorites it is quite common, since iron oxidizes in contact with oxygen, but in space this does not happen”, says the professor, who continues: “There are also terrestrial materials that are attracted to magnets, such as magnetite, molten iron and scrap from steel mills that form iron alloys. Not everything that is attracted to it will be a meteorite, but this is a good feature to start with.”

Therefore, to really classify a found fragment as a meteorite, combining characteristics and tests is the most effective way. You can observe the density of the material, which, if it comes from space, will be much heavier compared to terrestrial rocks of the same volume. In addition, Lucelene says that, “if the meteorite has a recent fall, another good feature is the melting crust. Contact with the atmosphere causes it to heat up and melt, but before it reaches the ground it cools down completely and forms the crust. It is a black and very thin material, typical of meteorites. No terrestrial rock has the same.” The interior of the extraterrestrial item is also of important analysis. “It’s worth breaking a little tip of the meteorite and sanding it to see what it’s like inside. Some features you can observe with the naked eye or with a magnifying glass:

Although such characteristics help in the identification, the proof and cataloging of the meteorite will only come after performing sophisticated tests in the laboratory. “The main tool for classifying meteorites is petrographic microscopy. It is a technique that requires knowledge, training and must be performed by specialists”, says Professor Rojas. For this, it is necessary to send 20 grams or 20% of the supposed celestial body for analysis and deposit in museums. The rest of the piece can remain with the person who found it, says Gabriel Gonçalves, who opened the interview. “We don’t have a specific law for this, but some countries, like Argentina, say that meteorites belong to the Union. In Brazil, we reflect the jurisprudence of American law, which basically says that the owner of the meteorite is the owner of the land where it fell.”

What to do if you find a meteorite?
Contrary to the viral images on the internet, washing the rock fragments is not recommended, as it accelerates a process of weathering and wear. “If you find it, you have to store it properly, protect it against moisture, avoid handling it. This preserves the structures that will be important for the study of this rock in the future”, explains Lucelene.

The study of meteorites is essential for the understanding of space phenomena. The estimated date of formation of the Solar System, for example, comes from dating the age of the oldest meteorites. “The vast majority of the fragments are 4.5 million years old, and they carry extremely valuable evidence for the study of that time”, explains Rojas. The technique, known as comparative planetology, can also be applied to the analysis of terrestrial phenomena. “We researchers have a lot of doubts about the Earth’s core because we can’t access it. But we have access to samples of metallic meteorites, which are equivalent materials. Much of what we know about the Earth’s core comes from this analogy”, says the professor.

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