A bright meteor streaked across the sky over Spain. An Australian tried to extract gold from a meteorite. A micrometeoroid damaged the mirror of the James Webb telescope.
Occasionally, you come across news headlines like this. It is easy to see why they can be confusing; they use similar terms with completely different meanings. Today, we are going to discuss the difference between the two: how a meteor differs from a meteorite, why the Perseids are not a meteor shower, and what the problem is with using the term asteroid.
What is a meteor?
Let’s start with meteors. Contrary to a very common misconception, meteors are not celestial bodies falling to Earth, but a luminous trace that appears when they enter the atmosphere. When we see a shooting star in the night sky, it is a meteor.
Source: Nicholas Roemmelt
The sources of the vast majority of meteors are tiny objects no larger than a grain of sand. But of course, sometimes larger objects fall to Earth and produce much brighter meteors. If the brightness of a meteor exceeds -4 star magnitude (that is, it is brighter than Venus in the night sky), it is called a bolide. If its brightness exceeds -17 star magnitude (that is, it is much brighter than the Moon at full moon), then we are talking about a superbolide.
What is the difference between a meteorite and a meteor?
If a meteor is just a glowing trail in the atmosphere, what is a meteorite? It is simple. A meteorite is a celestial body that has reached the surface of the Earth. We can talk about the whole object, as well as the debris left after its destruction in the atmosphere.
In this regard, it is rather ironic that the most famous meteorite in history is not a meteorite. It is about the so-called Tunguska event, which is more correctly called the Tunguska phenomenon. The fact is that the celestial body that produced it exploded in the Earth’s atmosphere before reaching the surface, and so far, no one has been able to find any of its fragments.
But the situation with the Chelyabinsk meteorite is different. Like its Tunguska “colleague”, it too exploded in the atmosphere. However, several fragments with a total mass of 654 kilograms (with the original mass of the object of 9100 tons) still managed to reach the surface. So in this case we can really talk about a meteorite.
What is the difference between a meteor shower and a meteorite shower?
This brings us to the next question: What is the difference between a meteor shower and a meteorite shower? Again, although the terms sound very similar, they mean very different things.
Source: Stocktrek Images, Inc. / Alamy
A meteor shower is a phenomenon where, over some time, many meteors “fly out” from a single area in the sky called a radiant. Such a stream occurs when, in its motion around the Sun, the Earth passes through a plume of dust left by a celestial body. Most often, these are comets, but sometimes asteroids can also be their sources. Therefore, meteor showers are a regular and predictable phenomenon. Each stream is observed at a strictly defined time of the year and has its peak. For example, the famous Perseids decorate the sky from mid-July to the end of August, and the maximum of their activity usually falls on August 12.
A meteorite shower is completely different. It refers to the multiple simultaneous fallout of meteorites due to the destruction of a large celestial body in the Earth’s atmosphere. The Sikhote-Alin meteorite is an example. On February 12, 1947, in the mountains of Sikhote-Alin in the Far East fell several thousand iron-nickel fragments fell with a total mass of more than 30 tons. This event is considered one of the largest meteor showers in the history of mankind.
What are meteoroids?
We have already dealt with meteors and meteorites. Now it is time to talk about meteoroids. According to the current definition of the International Meteor Organization (IMO), a meteoroid is a solid object moving in interplanetary space, whose dimensions range from 30 microns to 1 meter. Thus, we can make the following logical chain: a meteoroid entering the Earth’s atmosphere generates a meteor, and fragments that reach the surface become meteorites.
You may also sometimes see the term micrometeoroid. It is not official – IMO abandoned its use in 2017 as redundant. However, this does not prevent various organizations, including NASA, from using it. Micrometeoroids are small meteoroids. Since the term is no longer official, there is no formal definition of the size of a micrometeoroid. But, as a rule, they are understood to be objects up to a few millimeters in size.
What is an asteroid?
In conclusion, let’s talk about asteroids. It may seem strange, but this term does not have any formal definition. In the past, the International Astronomical Union used the term “minor planets”, which was considered synonymous with the concept of an asteroid. However, in 2006, it was replaced by the term “small body of the Solar System”. According to the official wording, they include all celestial bodies that are neither a planet, nor a dwarf planet, nor a natural satellite. Thus, the category “small bodies” includes asteroids, comets, and all other types of objects inhabiting the Solar System, from centaurs to bodies beyond the orbit of Neptune.
As in the case of micrometeoroids, the lack of a formal definition does not prevent scientists from actively using the term asteroid. As a rule, they are called objects that are larger than a meteoroid and are not comets – that is, do not demonstrate their characteristic features in the form of coma and tail.
However, if you dig a little deeper, you will discover a lot of nuances. For example, a comet can “burn out” – completely deprived of all volatile substances and cease to demonstrate any activity. There are also centaurs – objects that are transitional in their properties between asteroids and comets. In turn, the icy objects of the Kuiper belt do not demonstrate cometary activity simply because they are at a very great distance from the Sun.
Therefore, in order not to be confused by the numerous nuances, for simplicity, we can consider that asteroids are objects that meet the following criteria:
- Their dimensions exceed one meter;
- Their orbits are less than 5 a.u. from the Sun (about the radius of Jupiter’s orbit). This is the distance from which ice does not vaporize even when exposed to direct sunlight;
- They show no signs of cometary activity.
