Little Meteor Science

An asteroid is a solid object in space that is discovered by astronomers. Solid objects in interplanetary space, which orbit the sun similarly to planets, can be composed of various metals (primarily iron and nickel), rocks (undifferentiated chondrites or differentiated chondrite melts), or ice masses. Here, ice describes not only water in the solid state but also all liquids and gases that can exist as solid masses in space. Asteroids, however, are primarily those objects that predominantly conceal metals and rocks inside. They are mainly located in the asteroid belt between Mars and Jupiter or primarily orbit in the inner solar system. Asteroids do not lose mass through the outgassing of ice masses, even near the sun, which distinctly sets them apart from cometary materials. An asteroid is also referred to as a minor planet or planetoid. These cosmic objects can be monolithic (a large rock) or consist of many fragments (a rubble pile of variously sized chunks).

A comet nucleus is a fully solid object in the distant, cold outer planetary system. There, it would be a normal ice body, and astronomers could not distinguish it from other asteroids. However, a comet is usually only discovered by astronomers when its cometary materials are so strongly heated on their orbit around the Sun in the near-sun space. This causes that comet nucleus with coma and tail to travel through space, shining much brighter than before. Solid objects in the outer interplanetary space, which orbit the Sun like asteroids, can consist of various metals and rocks, but they are primarily composed of ice masses. Ice here does not only describe water in its solid state but all liquids and gases that can exist as solid masses in space. Comets are cosmic wanderers that, at least temporarily, form an atmosphere on their orbit around the Sun, the so-called comet coma, because certain ice masses become fluid due to solar radiation. Since the outflowing gases can also carry tiny solid particles from the comet's surface, the coma filled with gas and dust is clearly visible and spatially much larger than the solid comet nucleus. However, this rather small nucleus does not have the strength to permanently hold an atmosphere. The solar wind drives away gas and dust, creating the comet tail. The gas is always blown away perpendicularly from the Sun and ionized. This part of the comet's tail (ion tail) thus shines itself and always points linearly away from the Sun. The dissolved dust is also accelerated and sorted out by the solar wind over time, forming another rather curved tail, which fans out between the ion tail and comet's path. Thus, every comet leaves a trail of dust particles in the traversed space. Each of these particles is also referred to as a meteoroid in meteorology, as they will produce a meteor when they plunge through an atmosphere. The comet thus continuously loses mass in the form of gas and dust on its orbit around the Sun. A comet dies when its ice masses are completely used up, at least on the near surface. The remainder continues to exist as a normal asteroid or a burned-out comet nucleus.

A meteor is the brief luminous phenomenon that appears in the sky when a meteoroid enters the Earth's atmosphere. Commonly, a normal meteor is referred to as a shooting star. It flashes briefly and seemingly colorlessly for one or two seconds in the night sky, shining as brightly as a star. It can be observed as a faint line or a rapidly moving point. A very bright meteor can be referred to as a fireball or bolide. Sometimes, one can also observe the afterglow of the meteor's trajectory. The responsible meteoroid passes through very high atmospheric layers during its flight through the Earth's atmosphere. The start of this luminous event can indeed be at an altitude of 200 km. Normally, meteors glow at altitudes between 130 km and 70 km above the Earth's surface. The terminal height of a large detonating meteor falls well below the stratopause. In a normal meteorite fall, the meteor phenomenon can be observable down to an end height of 10 km, often resulting in a meteor cloud.

A meteorite is essentially an object from space that can only be discovered on the Earth's surface. It is exactly the part of the meteoroid that survived the plunge through the atmosphere and ultimately reached the Earth's surface as a solid object. It must not be confused with the meteor, the light event. Meteorites are almost unchanged samples of a parent body from our planetary system, which were more or less altered during the formation of the solar system. Basically, there are stone, stony-iron, or iron meteorites. They are often very compact and noticeably heavy. A complete meteorite always has a very thin melt crust shortly after the fall, which often appears blackish and conceals the still present alien material inside. Meteorites are usually very susceptible to oxidation and weathering. Especially because iron is often present, a magnet reacts to the material.

A meteor shower is a kind of "cloud" or "tube" of meteoroid particles on approximately parallel or similar orbits around the sun. When the Earth passes through such an area, meteors appear more frequently, radiating from a radiant point. A meteor shower is named after the constellation in which the radiant is located. Such a shower is formed when a comet, during its journey around the sun, especially near the sun in the inner solar system, loses many small particles of frozen gases and dusts. For this reason, a meteor shower typically has a variable shower density.

A meteor cloud is only created by a very deeply penetrating meteoroid with high ablation and does not glow by itself. Therefore, such a dust and haze cloud can be best observed during the day or twilight. Such an initially linear cloud envelops the heated entry channel and can change over time due to convection. However, the intruder cuts through many air layers on its flight from top to bottom. As a result, over time, every meteor cloud is distinctly dispersed by high-altitude winds. An increasingly chaotic "zigzag" cloud band forms, which can even overlap itself for perspective reasons.

The afterglow of a meteor can last a few seconds, but also many minutes, and is mainly observed at night. The meteoroid went through a phase of maximum ablation, especially in the ionosphere. The glow is the emission of light during the recombination of electrons in the active atomic shells, which is visually seen as rather colorless but can be documented photographically as quite colorful. Here too, as with the meteor cloud, the afterglow of the meteor's trajectory is initially linear. But the high-altitude winds quickly blow the glow into a chaotically distorted "zigzag" cloud band.