Meteoroids, meteors, and meteorites: how do they differ?

This phenomenon, the arrival of meteoroids on Earth, is more frequent than it seems. Most of those that pass through the Earth's atmosphere are microscopic particles. 50 to 230 meteoroids over 10 grams arrive every day. Those that measure 50 meters or more in diameter and that do not disintegrate are nevertheless the ones that scientists are most concerned about since the impact against the Earth's surface would have devastating consequences for the planet as it has in the past.

The scientific community has been studying the objects that arrive or orbit the Earth for decades. These external objects, if they exceed 100 meters in diameter, are called asteroids, while if they are smaller and have the possibility of entering the atmosphere, they are meteoroids. The light phenomenon that the meteoroid produces when it enters the atmosphere is called a meteor. A fireball is a very bright meteor.

The scientific community has been working for decades to study the various objects that arrive at or orbit the Earth.

When the meteor enters the atmosphere, it 'survives' at the entrance and 'hits' the ground, it is called a meteorite. It is, therefore, the stone that is preserved, the one that scientists study and the one that, sometimes, is the object of desire on the part of the collectors who travel the surface of the planet looking for these coveted pieces of rocks coming from space. The term meteor shower is not correct. It's a meteor shower. The Perseids or St. Lawrence Tears that are recorded every year when the Earth passes through a cloud of tiny particles is actually an entry of material so small that it may not survive.

As a result, there are no meteors left from that shower. They're also called a star shower, even though it's not the stars we're seeing either. It is, on the contrary, a shower of particles. Only if what comes in at a size of ten centimeters or more is it dominated by a fireball.

When these tiny particles move at high speed, about five kilometers per second, they produce friction through the air, at about eighty kilometers high, and enter the atmosphere. This phenomenon is called ablation and produces a lot of light around the object. In all the bodies that enter the atmosphere, this phenomenon takes place, but also on Mars, in Venus or in the Sun. In fact, the entry of particles has been detected and meteorites have been found on the surface of Mars.

How many enter, where, and what they are composed of?

The total mass entering the Earth's atmosphere is estimated to be in the order of 37,000-78,000 tons per year (100-215 tons per day), although most are microscopic particles. Extrapolating to the entire area of the Earth, it is estimated that 18,000 to 84,000 meteoroids greater than 10 grams per year, or between 50 and 230 meteoroids per day, are present. Only those that exceed one kilogram do not disintegrate.

68% of the meteors found are located in Antarctica because they are easily found on its surface. On the other hand, another 14% of the findings are in the deserts of North Africa. 85% of them are composed of rocks called ordinary chondrites, the same type of material that has formed the solar system. The remaining 15% are divided into a wide variety of materials: rocky, metal-rich, and metallic.

One of the most widespread is that the meteorite is hot when it is found or that it produces a huge crater.

One out of every ten meteorites found comes from the breaking of what is called a differentiated object. The planet Earth, for example, is a differentiated object because it is made up of a core, a mantle, and a crust. Meteorites can also be classified according to the area from which they came from the original body. Those coming from the core of the original fragmented asteroid are composed of iron (ferrous); those from the transition zone between the core and the mantle, are the metal-rich ones; the rocky ones come from the part of the mantle and the basaltic ones come from the crust. They are a great source of information because these rocks have been formed at the origin of the solar system and have not been altered.

False myths

There are certain myths about meteors. One of the most widespread is that the meteorite is hot when it is found, that it produces a huge crater, that it is all burned up. Although during the process it gets very hot, over 1,000 degrees of temperature in the atmosphere, only a very thin layer of the meteoroid is heated and when it reaches the Earth, it quickly cools down as it falls.

At 25 or 30 kilometers from the surface, the temperature is very low, so when it reaches the ground, it is already cold. The cinema has motivated some of these myths like the one that "everything falls in New York". If one compares the area of the cities with the total area of the Earth, the probability of a harmful object falling into the sea is much higher. Of course, no one place has more falls than another. They enter any part of the earth's surface, day or night.

Meteorite concept

Among the tons of extraterrestrial material that reach the Earth's surface every day, only 1% is recovered. This material includes fragments of asteroids, as well as rocks from the Moon and Mars, and interplanetary and cometary dust. Fragments of asteroids and planets that travel through space, and crash into the surface of the Earth or another planetary body, are called meteors, where they are recovered. The mass varies from a few grams to tens of tons.

The larger ones are responsible for the formation of large impact craters. A meteorite seen hitting the ground is called a "fall," while one discovered later is known as a "find. When meteorites enter the atmosphere, friction with the air begins to heat the rock, producing the light phenomenon known as "shooting stars. This heating leads to the fusion of the rock so that if the specimen is small, it will completely vaporize and only the largest rocks will survive this process, falling to the earth's surface.

For this reason, meteorites have a fusion crust, which reflects their friction with the atmosphere. Those meteors whose luminosity is superior to that of the planet Venus will be called bolides. Meteorites are always named after the place where they were found, usually a nearby city or some geographical feature. In cases where many meteors are found in the same place, the name may be followed by a number or a letter. Meteorites have been observed and collected for thousands of years and scientific research has been carried out for over two hundred years.

Meteorite craters

When a meteorite hits the Earth's surface, the kinetic energy released in that impact is estimated to be between 10 and 10 ergs. This is instantly transferred to the ground by a shock wave, which intensely fractures and disintegrates the rock around the point of impact. A similar shock wave takes place in the meteorite so that it fragments into thousands of pieces and volatilizes. When this happens, large amounts of fragmented debris are thrown out, while solid bedrock is deformed up and out, and the crater rim is formed. Large volumes of rocky material fall back into the crater and fill the bottom, where molten rock can be buried.

The Chicxulub crater is located northwest of the Yucatan Peninsula in Mexico. It measures more than 180 km in diameter and is one of the largest impact areas in the world. The bolide that formed the crater is estimated to be at least 10 km in diameter. Recently, the hypothesis has been reaffirmed that the impact is responsible for the mass extinction of the Cretaceous-Tertiary, killing off the dinosaurs, among others.

Some critics argue that the impact was not the only reason for this extinction, although it may have contributed to a significant change in the composition of the atmosphere at that time, making the living conditions of many species more difficult.

Meteorite classification

Meteorites can be classified into three large groups according to their modal abundance in metal: ferrous or SIDERITES, petroliferous or SIDEROLITES, and stony or lithium or AEROLITES

SIDERITES: They contain more than 90% of Fe-Ni. SIDEROLITES: Contain 50% Fe-Ni and 50% sulfides and silicates. There are two subgroups: MESOSIDERITES and PALLASITES. AEROLITES: Contain less than 50% Fe-Ni. They are subdivided into: CONDRITES (approximately 10% Fe-Ni. They present small spheres of variable texture and composition called conundrums) and ACONDRITAS (less than 1% Fe-Ni. They do not present conundrums).