Meteoroid

Meteoroid is a solid object that moves in interplanetary space and whose size is considerably smaller than an asteroid and considerably larger than an atom or molecule.

The most accepted definition today was proposed in 1995 and determines that the size of the meteoroids is in a range between 0.1 mm and 10 m.

If the size is larger, it is called an asteroid; and anything smaller is considered interplanetary dust.

In the cover image you can see the spectacular trail of light; over the ALMA ensemble is a shooting star, gliding across the scene in a trail of vivid colors.

Emerald greens, golds, and faint crimson hues glow brightly as the meteor, on its fiery journey through the sky, burns through Earth’s atmosphere.

As the speeding fireball – which is actually a small rocky grain from interplanetary space – interacts with the atmosphere, it heats up, causing its uppermost layers to evaporate and leaving them behind in the form of a glowing trail.

These traces disappear in a few seconds, but in this image they have been captured with a single “click”.

As they rise above the horizon, Spica, the brightest star in the constellation Virgo, and our neighboring planet, Mars, glow in the center of the image as cosmic spectators of this fiery descent.

Canarias
The meteor that was seen in Gran Canaria on November 3, 2015. Credit: web “cadenaser.com”

When meteoroids enter Earth’s atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or “shooting stars” are called meteors.

When a meteoroid survives a trip through the atmosphere and hits the ground, it’s called a meteorite.

Where do the meteoroids come from?

Most of the meteoroids that move in interplanetary space are fragments of comets and asteroids.

They may be rocks that, due to some phenomenon, have been detached from a planet or one of its moons.

They can also come from comets that, due to solar heat, leave behind a jet of dust and rocky material released from the vaporizing ice.

Shower of stars

If the Earth crosses the orbit of a comet, these debris cause an increase in the number of meteors that reach it; they are the typical meteor showers.

On certain dates, such as the night between December 13 and 14, there is a shower of shooting stars. They can be seen up to 60 in an hour.

Shower stars
Perseid meteor shower peaks overnight. Credit: web wtkr.com. Author: Maddie Kirker

During meteor showers or shooting stars, which normally last a few days, most appear to come from a certain point in the sky, called a radiant, but this is an optical illusion.

These meteors essentially move in parallel paths; But, when they are observed from a certain place on the Earth’s surface, because of perspective, these parallel trajectories seem to come from the same point.

Meteor showers are usually named after the constellation where the radiant point is located.

Geminid
Geminid meteors. This diagram is meant only to show their divergence from the radiant point.  Credit: Sky & Telescope/Gregg Dinderman

The meteors’ perspective point of origin is called the shower’s radiant. Don’t expect to see several meteors at once!

The Geminid meteor shower is one of the best known. It starts each year around December 11 and lasts until December 15.

As its name indicates, the radiant point is located in the constellation of Gemini.

The aeroliths or meteors

When a meteoroid passes through the atmosphere it is called an aerolith (stone that crosses through the air) or meteor.

When the meteor comes into contact with the atmosphere, at heights of between 80 and 100 kilometers, the strong friction with the air causes the meteor to heat up and burn, emitting light and transforming into a fireball.

Between 50,000 and 100,000 fireballs enter the atmosphere each year.

Often during meteor falls, explosions and hissing sounds are heard that can be caused by shock waves resulting from the fragmentation of the meteor.

When a meteor has a mass greater than about 10 grams, upon entering the Earth’s atmosphere the light trail that it leaves behind persists for several minutes, even for half an hour.

It can be as bright as Jupiter or Venus, and can be accompanied by acoustic phenomena similar to an explosion.

These meteors or aeroliths that stand out due to their great brightness are also called bolides. The only difference between shooting stars and fireballs is that they have a greater mass.

The meteorites

The meteor that reaches the surface of the Earth, without having completely vaporized, is called a meteorite.

It is estimated that each year about 500 meteorites fall to the ground, of which 1% are recovered.

Arabia
Meteorite find in situ on desert pavement, Saudi Arabia. Weight 408.5 grams.Credit: en.wikipedia.org

The size and type of crater produced by a meteorite depends on the size, composition, degree of fragmentation, and the angle of entry.

Meteorite impacts that arrive at high speed are normally caused by iron meteoroids, which are more resistant and travel intact through the Earth’s atmosphere.

Crater
Barringer Crater, in Arizona, is the best preserved meteorite impact site on Earth. Diameter 1186 m. Depth: 170 m. Credit: es.wikipedia.org

Meteorites have also been found on the Moon and on Mars.

Most of these meteorites only leave a small hole, which does not mean that some have caused damage in the places where they have fallen.

On the other hand, stony or icy bodies, even though they are relatively large and weighing several tons, are stopped in the atmosphere.

Therefore, although they produce large craters, they are totally destroyed and no remnants of the meteorite are found.

Meteoroids that experience fragmentation in the atmosphere can fall like a meteor shower, which can vary from just a few rocks to thousands of pebbles.

In the province of Chaco, in Argentina, there is an extensive plain called “Campo del Cielo“. There is the second largest known meteorite. Its crater was discovered in 1969.

Chaco
The Chaco meteorite, in Argentine. It hasan approximate weight of 28,840 kg. Credit: es.wikipedia.org

Approximately 86% of the meteorites that fall on Earth are composed mainly of silicate minerals.

They appear to come from the asteroid belt and the Moon, as they include rocks similar to those brought to Earth by the Apollo and Lunik programs.

They also contain small amounts of organic matter, which includes amino acids.

They are 4.5 billion years old and are thought to be ancient materials from the asteroid belt, which did not form planets.

The rapid availability of large numbers of meteorites that could be found relatively easily in places that were easily accessible in African deserts led to the rapid increase in the commercial collection of meteorites.

Meteorite Moon
This meteorite is known as originated on the Moon. Credit: en.wikipedia.org

This trade increased significantly when some meteorites from the Moon and Mars were discovered in Libya.

Most of the material is sold to private collectors, especially in Algeria, Libya, Oman and Morocco.