Comets have always been a mystery to humanity, at least until 1606, when the first telescope was created and we were able to begin to study the true nature of comets and thus learn about the parts of a comet.
But, before that point, it could mean anything. Passing through different times and cultures, space comets and other visitors from deep space were synonymous with natural catastrophes, the harbinger of an important event, signs of the wrath of the gods, etc. The point is that many cultures gave different meanings to this cosmic element.
But, to begin to study them and understand their nature, we first have to understand what a comet is.
How much do you know about the galaxies that make up our universe? Don't miss our article where we tell you how many types of galaxies exist in our universe.
What is a comet?
A space comet is a celestial body , very common in our solar system and in virtually any other planetary system similar to ours.
Comets are celestial bodies that orbit stars, such as planets, asteroids, and planetoids. They are solid objects, formed by varied compositions of ice, rocks and space dust.
The movement of comets in the solar system follows a highly eccentric parabolic path, meaning that their orbital motion around the star can be greatly opened or closed depending on the gravitational forces of larger celestial bodies influencing them.
Due to their wide trajectory, comets can get very close to the solar surface, changing their physical composition as their matter sublimates. This means that the ice or minerals in its core change from a solid state to a gaseous state without going through a liquid state.
The most important distinctive feature of comets is their tail, which is formed due to the scourge of solar winds, which displaces the gaseous matter surrounding the comet, creating a trail that follows it throughout its journey and can be seen with the naked eye. .
The astronomer Edmund Halley was the first scientist to propose, in the 18th century, that comets do not move freely through space, but have a defined orbit and can therefore be seen from Earth at certain times.
In fact, in 1705 he predicted the appearance of a comet in 1758. His forecast was correct and here
That comet is now known as Halley's Comet . Sadly, Edmund did not live to see his theory fulfilled.
Comets are much more complex celestial bodies than you may be thinking, since not all of them are simple stones that wander through space.
Understanding the composition of comets is a fascinating topic and a crucial area of research in modern astronomy. If you'd like to learn more about their constituent elements, you can consult our article on the composition of comets.
What are the parts of a comet?
As we have mentioned, telescopes have allowed us to take a much closer look at space comets and because of that, we have been able to get to know them much better and identify the way in which they are composed.
Any space comet is essentially made up of three parts : the nucleus, the coma, and the tail; the latter, in turn, is divided into two different parts: dust tail and gas tail.
Let's see what each of the parts of a comet consists of
Core
The nucleus is the center of a comet and contains most of its matter. The composition of a comet's nucleus can vary, but it can generally be described as a giant rock of ice.
However, the internal composition of ice is highly variable, usually made up of a combination of frozen water, methane, iron, sodium, magnesium, silicate, and other highly volatile minerals.
The size of comets is measured by reference to the diameter of their nucleus (not the length of their tail, as some believe). Comets come in all shapes and sizes, but on the known scale, these rocks can measure between 1 and 150 km in diameter.
Coma
The coma is another part of comets and refers to the gaseous halo that surrounds the nucleus. This can get bigger or smaller according to the proximity of the comet to the sun, which causes much of its mass to sublimate and become a gas cloud made up of different elements.
The coma surrounds the nucleus at all times during the comet's trajectory, however, when they meet the currents of solar winds, they push the gases towards the back, which creates the long trail of dust and gases that we know as " the tail of the comet.
Glue
The tail is the most characteristic part of comets, its parabola-shaped trail is what allows us to differentiate them from other celestial bodies with the naked eye at night (even during the day when they are very bright), and it was also, without Without a doubt, the feature that caught the attention of our ancestors was seeing comets pass by.
The interesting thing is that comets actually have two tails , or at least one tail made up of two different segments. Sometimes both tails align in the same direction, while at other times they can have different orientations, making them much easier to identify.
The first part, that is, the dust tail, is made up of dust debris pushed along by solar winds.
The second tail is known as the Ion tail. It is made up of residual gases with ionized particles, which are the product of the sublimation of the solid components of the nucleus when it gets too close to the sun.
Therefore, when comets are passing closest to the Sun's orbit on their path, the Sun will lose some of its matter as a result of heating of the frozen materials, causing the tail or tails (in case have two) leave a much longer trail.
For example, Comet West was a Giant Comet, sighted in 1976. Its magnitude was so great that it left a trail 29 million kilometers long as it passed through our solar system.
queue direction
It is normal to believe that the tail of comets is oriented in the opposite direction to its movement, because that is what would happen inside our atmosphere.
However, it is not that simple. First, the cometary tail of ionized gases assumes its orientation according to the comet's position relative to the sun. This will always be in favor of the direction in which the solar winds blow.
On the other hand, the dust tail does obey the inertia of the movement, aligning itself at some intermediate point between the opposite direction to the displacement of the nucleus and the gas tail.
Comet classification
We have told you that comets can differ a lot from each other according to their size. There are relatively small ones and others truly huge, which could end all life on our planet if they were to make a direct impact.
1 – 1.5 Km – Dwarf Kite
1.5 – 3 Km – Small Kite
3 – 6 Km – Medium Kite
6 – 10 Km – Big Kite
10 – 50 Km – Giant Kite
+50 Km – Goliath.
Where do space comets come from?
Short-period comets formed in the Kuiper belt, on the outskirts of our solar system.
Our galaxy has its own source of comets, asteroids and other cosmic objects, which in astronomy are known as " Trans-Neptunian Objects", that is, matter that originates beyond the limits of our solar system.
In the case of comets, those that enter our planetary system usually originate from two different points.
Oort Cloud
The first of these is the Oort Cloud, a spherical formation of matter located just one light-year from our sun.
It is believed that this giant cloud of matter can measure up to 50.000 Astronomical Units, is spherical in shape and is made up of a massive accumulation of cosmic matter, mainly ice rocks, methane, carbon monoxide and ammonia.
It is believed that the Oort Cloud is where long-period comets originate, that is, comets that have trajectories so open that they can take thousands of years to complete a single return to their own orbit.
A clear example is the famous Hale-Bopp comet, which passed relatively close to our sun in 1997 and created an unparalleled spectacle due to its incredible brightness and long tail.
Hale-Bopp will take about 3200 years to complete its orbit and be able to be seen again near our solar system.
An interesting fact is that this super bright comet created a huge stir in people all over the world. Some even taking it as a supernatural sign.
During its sighting in 1997, members of the Heaven's Gate sect committed mass suicide, claiming that they would abandon their bodies in order to travel to the cosmos aboard the comet.
Kuiper Belt
The Kuiper Belt is a disk formed by interstellar matter that orbits around our sun, just beyond the limits of our solar system; therefore, its matter is cataloged as Trans-Neptunian Objects.
The Kuiper belt is believed to be the place of origin of all short-period space comets, that is, those with slightly eccentric orbital paths and take a very short time to complete one cycle of trajectory.
NASA sent a space probe in 2006 to explore the Kiuper Belt Objects (KBOs). The probe reached Pluto in 2015 and it is expected that it will soon be close enough to the disk that surrounds the solar system to provide exact information on the amount and type of matter it contains.
Probably the most popular short-period element is the famous Halley's Comet, discovered in 1705 and completing a cycle of its trajectory every 76 years.
Halley's Comet has been a true gem of astronomy for a couple of centuries because its study has shed great light on our knowledge of celestial objects.
A curious fact is that, although Edmund Halley "discovered" his comet in 1705, it was later discovered that it had been observed many times since 266 BC by the Chinese and Greeks. In fact, for many cultures it was an omen of war or disease.
Halley's comet for the Greeks
Halley was a complete disaster for the Greeks in the year 466 BC, so without a doubt the appearance of celestial bodies on earth began to be interpreted as a sign of catastrophe.
At that time, the tail passed just above our planet, resulting in a constant meteor shower for more than 3 months.
Many Greeks, including Aristotle, tried to reflect and seek an explanation for this issue, which would be resolved almost two millennia later thanks to Galileo.
When does Halley's Comet pass by?
Halley's Comet is one of the short-period comets, which means that it can be seen "frequently" close to the orbit of our sun. In the case of Halley in particular, it is visible from Earth every 75-76 years.
The last time Halley visited us was in 1986 and astronomers have predicted that its next sighting will be in 2062.
the death of comets
When a comet runs out of volatile gases, it dies. From now on it will be an asteroid.
Nothing in the universe lives perennially, neither do the planets, nor the stars… and neither do the space comets.
The life of space comets depends on the loss of matter as they approach hot stellar atmospheres. This process causes the solid mineral compounds of the comet's nucleus to begin to sublimate, turning into gas clouds that will later go on to form its ion tail.
However, comets have no means of recovering lost matter, so they get smaller and smaller with each cycle of their trajectory.
When comets are old and have completed several cycles of their own orbit, they will lose enough matter to run out of volatile elements, such as methane gas. At that point, comets as we know them will die and become simple asteroids, a rock floating dead in space.