What is a comet?
Comets are very common celestial bodies, residual parts of the formation of other superior bodies and that generally inhabit the outskirts of planetary systems like ours.
A comet is much more than a rock that floats lost in space, in fact, they are residues of matter that did not manage to form higher celestial bodies, such as moons or planetoids, since they are basically made up of the same elements.
In general, these space objects are a compact mass, made up of ice, rock and a multitude of volatile gases trapped inside their core: methane, carbon dioxide, carbon monoxide, ammonia and some silicates.
The main feature that differentiates comets from other small space bodies, such as asteroids or some planetoids, is their tail. A long, parabolic-shaped trail, which detaches from the core with movement (or so it was believed).
In addition to turning them into a great show in the night sky, the tail of comets has been the key that opened the doors to the knowledge we have gained about them today.
Are you interested in learning more about comets? Then keep reading this article until the end, where we'll teach you everything about comets and their characteristics.
If you are passionate about comets, asteroids and other celestial bodies, you may also be interested in reading our special article on the parts of a comet.
characteristics of a comet
physical composition
As we mentioned, the comet's tail was the key that helped modern scientists unlock the secrets behind these striking space objects.
Contrary to what was believed in ancient times (and until the XNUMXth century), comets are not simply space rocks, in fact they are made up of different gaseous elements that are preserved in a solid state due to the low temperatures of deep space.
Thanks to several experiments recently conducted, especially the findings provided by the spacecraft , which managed to take physical samples from a small comet in 2004 and bring them back to Earth for study, we now know much more about the characteristics of comets.
What the Stardust spacecraft found on that mission, 16 years ago, was truly incredible!
The Stardust samples confirmed the most widely accepted assumptions about the composition of comets: traces of gases such as methane and CO2 were found in the samples, as well as iron and other minerals, but they also found something much more important.
Comet Wild 2 contained large amounts of the essential elements for life on Earth!
The experiment showed that part of the comet's chemical composition contained glycine, an essential amino acid that can be used to make different types of proteins that are very common in life on Earth.
This result finally confirmed the theory that the origin of life on Earth, more than 1.000 million years ago, was the product of space material obtained through the impact of comets and asteroids against our planet.
orbit of a comet
The orbital path is one of the most important features of comets and was discovered by Edmund Halley in the year 1682.
There are two types of orbital paths for comets; there are the short-period comets, which originate mainly in the Kuiper Belt, just outside our solar system, and also the long-period comets, which are thought to originate further out, in the Oort Cloud.
short orbits
Comets with short orbits are closer to our sun (only about 50.000 AU) and are eventually drawn into our system by the gravitational forces of the sun and planets.
Short-period comets show much more predictable paths and relatively fast orbits, taking between 3 and 200 years to complete a cycle around our sun.
long orbits
Long-period comets are much rarer, at least for us, and also much more unpredictable because their trajectory can be altered by a variety of factors.
However, we have never been able to see a long-period comet pass by twice because they have such wide orbital paths that it can take thousands of years before completing a single cycle.
Shape
Despite the fact that it looks like it in most graphs, the nucleus of space comets is not round, in fact they have completely irregular shapes, as is the case with any common rock here on Earth.
This occurs because the density of its mass is not capable of generating gravitational fields powerful enough to press its own matter towards the center, compacting it into a perfectly spherical shape, which is what happens with the planets or with almost any celestial body with more than 1.000 km in diameter.
Various studies on the shape of comets have shown that they tend to be more irregular, which is interesting for understanding their formation and evolution.
age of a comet
Comets are typically composed of very old space dust. In fact, it is estimated that the comets contained in the Kuiper Belt, on the outskirts of our solar system, are made up of material left over from the formation of our solar system, so their average age is estimated at about 4.500 billion years.
The cometary age is the table used to catalog different comets according to the estimated time since their formation.
Due to the long lifespans of these bodies, their age is measured according to the number of orbits they complete. This measurement is known as Cometary Years (CY).
- Baby Kite – +5 CY
- Young Comet – +30 CY
- Medium Comet – +70 CY
- Old Comet – Up to 100 CY
- Comet Methuselah – +100 CY
It has been possible to determine with relative accuracy the estimated age of some of the comets observable from Earth. For example:
Halley's Comet, with an orbital path that takes about 76 Earth years, is still a baby comet, with just 7 orbits completed.
On the other hand, Encke, a small, short-period comet, is cataloged as Methuselah, since it has completed more than 100 revolutions around our sun, which takes approximately 3 years.
size of comets
In space, dimensions are a curious thing. Thinking that something is "big" or "small" can confuse you a bit. The size of a comet is very difficult to average, because there are very small ones and there are others the size of entire planets.
In any case, the size of comets is measured using the diameter of their nucleus at the widest point as a reference. Thus, there are comets that can measure only 1km and others that are 100 or 200 times larger.
This is how comets are classified according to their size:
- Dwarf – Up to 1.5 km
- Small – from 1.5 to 3 km
- Medium – from 3 to 6 km
- Great – from 6 to 10 km
- Giant – from 10 to 50 km
- Goliath – from 50 km onwards.
History of the discovery of comets
The study of comets and their characteristics is not new to humankind. Virtually every culture throughout history has made assumptions about the nature of these celestial bodies. Most of these assumptions have been quite far from the truth.
The most important discovery in relation to comets was made by Edmund Halley in 1705, when he proposed that comets were not a sporadic phenomenon in the sky, but, in fact, maintain a fixed orbital path, like that of the planets in orbit. around the sun
He proposed this idea based on his study of the passage of the comet of 1682 that would later bear his name ( Halley's Comet ). Edmund used the Theory of Universal Gravitation to identify that this comet had the same gravitational path as the object seen in 1607 and predicted that it would be seen again in 1758.
Halley did not make it to the date of his gravitational theory of comets being tested alive, but his studies completely changed the conception of comets forever.
