According to the Dictionary of the Royal Spanish Academy, an asteroid is a “smaller body of the solar system, with dimensions less than 1000 km in diameter and that frequently revolves around the Sun between the orbits of Mars and Jupiter”. Basically, we are talking about a rocky object that is not large enough to be considered a planet.
As the astrobiologist Carlos Briones explains in his book Are we alone? In search of other lives in the cosmos , asteroids that are smaller than 50 meters are called meteoroids, and those granules below 10 micrometers would be cosmic dust. Furthermore, meteoroids can also come from comets.
And where are the meteorites? On some occasions, the trajectory of asteroids and meteoroids intersects that of the Earth, and these bodies can get caught in our gravitational field. “The moment a meteoroid comes into contact with the atmosphere it is called a meteor ”, explains Francisco Espartero, director of the University Master’s Degree in Astrophysics and Observation Techniques in Astronomy at UNIR. “Most of them disintegrate leaving a trail of light, and we see them as shooting stars. And when the meteor is big enough to be able to surpass the entire atmosphere without disintegrating completely, then it falls to Earth, now it does, in the form of a meteorite ”. In fact, and as Briones collects in his book, being purists the name of meteorite should only be given to those objects whose fall has been observed and documented, but this is estimated to only happen in one in ten cases.
Comets, giants of ice and dust
As explained on the NASA Space Place disclosure website, comets are objects that orbit the Sun, just like asteroids but, unlike them, they are made of ice and dust . Most of the comets that we know come from the Kuiper belt and the Oort cloud, regions located on the edge of our planetary system.
“When comets get close enough to the Sun, their nuclei sublimate and form an atmosphere of gas and dust that is ionized by interaction with charged particles from the solar wind,” explains Briones in his book. “This gives rise to a tail, hair or coma, from which its name comes.”
Over time, many comets can end up losing their volatile materials, which will sublimate and spread in space, and at that moment they will become rocky asteroids that no longer leave trailing signals. And conversely, some asteroids are ‘sleeping comets’, since they contain very significant amounts of ice in their rocky core and can be activated if they pass close enough to the Sun.
