The first thing we need to know is that the Asteroids They are rocky bodies with carbonaceous or metallic characteristics, smaller than a planet. However, they are also larger than a meteoroid and orbit the Sun in an orbit interior to that of Neptune. Most asteroids orbit between Mars and Jupiter, specifically in the region of the solar system known as the asteroid belt. However, others accumulate at Jupiter's Lagrange points, and most of the rest cross the orbits of the planets.
The origin of the word asteroid comes from the Greek ἀστεροειδής. This word means "star figure”, and refers to the aspect that they present seen with a telescope. The first time it was used was for william herschel in 1802, who actually coined it. However, for most of the 24th century, astronomers referred to them as planets. It wasn't until March 2006, XNUMX, that asteroids were also called planetoids or minor planets. However, these terms have fallen into disuse.
Ceres is the name of the first asteroid discovered for more than two centuries. After the redefinition of the planet in 2006, which reclassified this body as a dwarf planet, it is technically Pallas, which was found in 1802, the first asteroid discovered. During these two centuries the number of known asteroids has not stopped growing, reaching values of several hundred thousand. However, if all its mass were added, the equivalent would only give 5% of the mass of the Moon.
Moreover, the asteroid classification it is made based on its location, composition or grouping. And for the location, the relative position of these stars with respect to the Sun and the planets is taken as a reference. Regarding the composition, to know it, the data extracted from the absorption spectra are used. The groupings are based on similar nominal values of the semi-major axis, eccentricity, and orbit inclination.
You should also read: Hypergalaxy: Groups, clusters and superclusters of galactic groupings
As an interesting fact, before highlighting the four fundamental aspects of asteroids, it is important to mention that due to their diminutive size and great distance from Earth, almost everything we know about them comes from astrometric and radiometric measurements, light curves and spectra. of absorption. Gaspra, in 1991, was the first asteroid visited by a space probe, while two years later Ida was the first in which the existence of a satellite was confirmed.
These are the 4 fundamental aspects about asteroids
One: The asteroid name
Apart from what is mentioned above, that is to say that it comes from the Greek origin and that it was william herschel, who coined the term asteroids for these bodies in 1802; It is essential to note that in the same year, in May, Herschel proposed to the Royal Society in London that both Ceres and Pallas, the only asteroids discovered up to that time, were a new type of body, which he called Asteroids.
On the other hand, most scholars and astronomers of the time rejected Herschel's proposal as unworthy, ridiculous or unprecedented. Fact that was evidently common during the time, due to the lack of technology. For this reason they continued to consider them planets. Giuseppe Piazzi, discoverer of Ceres, was the one who used the term planetoid and only heinrich olbers he seconded Herschel.
The asteroid at the beginning of the XNUMXth century
After having defined the term "Asteroid", over the years Herschel began to have more collaborators and it was not until the beginning of the 2013th century, when that term began to be generalized in its entirety. Later, specifically in XNUMX, when Clifford Cunningham, at a meeting of the planetary division of the American Astronomical Society, argued that the original proposal came from the Greek specialist charles burney.
According to Cunningham, Herschel had asked several friends for suggestions, including Joseph Banks and Charles Burney. In accordance with this, Banks wrote to Stephen Weston, who proposed the name "aorate", and Burney wrote to his son proposing names like "stellula" in clear allusion to the tiny size of these bodies. Ultimately, it was Herschel who settled on the term "asteroid" as the best of a bunch of bad ideas.
Two: The discovery of asteroids
For several centuries, researchers wondered about the enormous void between the orbits of Mars and Jupiter. These scholars included astronomers, physicists, and mathematicians. However, it wasn't until the 19th century that Piazzi provided the first answer with the discovery of Ceres. The following century brought a major discovery, as astronomers knew of thousands of asteroids, mainly grouped in the so-called asteroid belt.
Later, with the advent of automated searches in the late 2012th and early XNUMXst centuries, the number of known asteroids skyrocketed. And in the registry of the year XNUMX there were more than six hundred thousand computed orbits.
The planet between Mars and Jupiter
The first to propose the existence of an unknown planet between Mars and Jupiter was Johannes KeplerIn addition, he was the one who studied the gap between the orbits of Mars and Jupiter. It's worth noting that this researcher hypothesized that an unknown planet must exist in that space, but added that one might not be enough. Other scientists later echoed this position.
Moreover, Isaac Newton He made a quite successful remark, since he believed that both Jupiter and Saturn had been placed by divine influence on the outside of the Solar System in order not to disturb the orbits of the inner planets. The philosopher Immanuel Kant pointed out that the empty space was in proportion to the mass of Jupiter and Johann Heinrich Lambert thought that the gap was perhaps the result of the expulsion of some hypothetical planet due to the gravitational influence of Jupiter and Saturn.
Further to these insights of scholars, in the eighteenth century several astronomers were willing to believe in the existence of multiple unknown planets in the Solar System. However, it was Johann Daniel Titius, in 1766, who was the first to provide the explanation for the distance between the orbits of Mars and Jupiter, which would eventually become known as the Titius-Bode law. The numerical relationship attracted the attention of Johann Elert Bode, who did not doubt its validity and published it in 1772.
In 1781, William Herschel discovered the planet Uranus, at the distance that the law foretold was the definitive confirmation of its reliability and reinforced the belief in the existence of a planet between Mars and Jupiter. Another of the astronomers who generate the most interest in the aspect of asteroids is that the one who took in the location of the planet was Baron Franz Xaver von Zach, director of the Seeberg observatory.
a locator map
Baron Zach, in addition to selecting the zodiacal region, also prepared a star location mapThis allowed him to determine the presence of new objects, and based on this, he even calculated a hypothetical orbit for the unknown planet. In 1800, after unsuccessful results, he managed to convince other astronomers to help him in the search.
On the other hand, on September 20, 1800, the Vereinigte Astronomische Gesellschaft. This institution is also known as the Lilienthal Society and was created for the purpose of mapping the region of the Zodiac down to the faintest stars. Among the founding members were Karl Ludwig Harding and Olbers, who would later discover one and two asteroids, respectively.
What these scientists did to achieve their goals was to divide the Zodiac into twenty-four equal parts and from there choose other astronomers until they completed the number of divisions. These astronomers are known as the celestial police, however, after this organization, several astronauts did not actively participate in the search. Among those who participated were Herschel and Piazzi, who did not receive a formal invitation to join the enterprise, although he eventually he was the discoverer of the new planet.
Ceres, the first asteroid
In the year 1801, while working on the composition of a star catalog, Piazzi found an object in the constellation of the Bull. According to what he managed to observe, during the study nights, the object moved on the stellar background. At first he thought it was a mistake, however later he came to the conclusion that he had discovered a cometLater, he announced the discovery to the press, which attracted several European astronomers. One of the astronomers on the team, Joseph Lalande, asked Piazzi to send him his observations.
The observations were later shared in letters with Bode and Barnaba Oriani, in which he mentioned the absence of nebulosity around the object. With the data that were contributed by Piazzi in his letter, Bode calculated a preliminary orbit. Months later he reported to the Prussian Academy of Sciences that the orbit was consistent with the missing planet between Mars and Jupiter and subsequently reported to Zach for publication in Monatliche Correspondenz.
One of the names that came to be proposed was the name of Juno for the new planet. However, Piazzi had already baptized his discovery as Cerere Ferdinandea in honor of the patron goddess of Sicily and King Ferdinand. Eventually, the astronomical community accepted the name Ceres as a diminutive of Piazzi's proposed name for the new object.
The calculation of the orbit that allowed the rediscovery of Ceres
A pivotal event in the history of science was when Lalande passed Piazzi's observations on to Johann Karl Burckhardt, who calculated an elliptical orbit from them and sent his results to Zach in early June. By the end of the month in which this event occurred, the astronomical community was convinced that Ceres was a new planet. However, Piazzi's delay in supplying the data of his observations succeeded in frustrating attempts to recover it.
Through a letter sent to Oriani on July 6, Zach criticized Piazzi for keeping his work a secret. By the end of August many astronomers, especially in France, doubted the existence of the object. Then, in the month of September, all of Piazzi's observations were published. Carl Friedrich Gauss calculated a new elliptical orbit which greatly improved the one previously obtained by Burckhardt, who actually worked with few observations.
In the month of December Zach got to see the dwarf planet, but the bad weather that there was during the following days prevented him from continuing with his observations. Finally, on December 31 Zach and on January 2 Olbers independently observed Ceres in the position predicted by Gauss's calculations, confirming the object's existence.
Pallas, Juno, Ceres and Vesta
Olbers himself later discovered Pallas and Vesta. In accordance with this, he proposed the first theory of the origin of asteroids. A few months after the recovery of Ceres, on March 28, 1802, Olbers found another similar object, but with greater inclination and eccentricity. Two days later he was sure that he was facing a new planet, which he called Pallas, because he observed that it was moving with respect to the background stars.
thousands of asteroids
Knowing already the first discoveries mentioned above, nearly forty years passed until Karl Ludwig Hencke found the fifth asteroid after five decades of intense search. This long period of time can be explained by three main causes. The first cause is that most astronomers, being influenced by Olbers's theory, made their searches in the same region of space in which the objects were discovered. first bodies.
On the other hand, in the second place, the systematic search for new planets was not considered an astronomical priority, as was the case a lot during that time, since the first bodies were found by accidentFinally, the third cause was the lack of good celestial charts that clearly showed the positions of the stars. This discouraged astronomers because they weren't sure they were looking at a new planet or star.
First asteroid discovered by astrophotography
Once they had access to an ever-increasing number of celestial charts, astronomers had the means to undertake the task with sufficient guarantees. Thus, by 1857, fifty had been discovered, and the hundredth was catalogued in 1868. On December 22, 1891, Maximilian Franz Wolf discovered Brucia through astrophotography, a technique that accelerated the increase in the list of asteroids.
The 1923th century was a great collaborator in the scientific aspect and specifically in the year 1985 they had already registered a thousand cataloged asteroids, and then in XNUMX they recorded asteroid number three thousand. At the end of this century, the refinement of the observation techniques and the use of automated programs, such as Linear and Spacewatch, exponentially increased the number of known asteroids.
At the end of the 1999th century, in 2002 there were ten thousand. Then, in 2005, fifty thousand were registered. The number one hundred thousand was catalogued in 2014 and by XNUMX there were already four hundred thousand catalogued bodies. Many estimates suggest that there are over a million asteroids with sizes greater than one kilometer. As the number of asteroids increased, astronomers questioned their origin. François Arago observed that the orbits did not intersect in the same region of space.
This cast doubt on Olbers' theory, however, Arago admitted that the intertwining of the orbits suggested some sort of relationship. Later, in 1867, Daniel Kirkwood postulated that asteroids had originated from a ring of matter that did not form a planet due to the gravitational influence of Jupiter. This theory eventually became the dominant one in astronomical circles.
The one who found that there were no asteroids whose translation periods had a relationship of simple integers with Jupiter, was Kirkwood himself. So there were gaps in the asteroid distribution. In 1918, Kiyotsugu Hirayama found similarities in the orbital parameters of various asteroids, concluded that they had a common origin, probably after catastrophic collisions, and called these groupings asteroid families.
Three: General characteristics of asteroids
It is essential to mention the characteristics of each of the asteroids discovered in universal space. These are smaller, rocky bodies that orbit the Sun at distances less than that of Neptune. Most Asteroids are located between the orbits of Mars and Jupiter. They have small sizes and irregular shapes, except for some larger ones such as Pallas, Vesta or Higía that have slightly rounded shapes.
It is estimated that its origin arises from the large body collision that did not form a planet due to the gravitational influence of Jupiter.
Shapes, sizes and mass distribution
Asteroids don't come in a single size; in fact, they range from the largest, 1000 km, to rocks just a few dozen meters across. The three largest asteroids are similar to miniature planets. This means they are more or less spherical, their interior is partially differentiated, and they are believed to be protoplanets. However, the vast majority of them are much smaller, irregular in shape, and are either surviving remnants of early planetesimals, or fragments of larger bodies produced after catastrophic collisions.
By far, Ceres is the largest. Next in size are Pallas and Vesta, both with diameters just over 500 km. Vest, on the other hand, is the only main-belt asteroid that can sometimes be seen with the naked eye. On rare occasions, near-Earth asteroids like Apophis can be seen with the naked eye. The mass of all main-belt asteroids is estimated to be between 2,8 and 3,2×1021 kg; or, what is the same, 4% of the mass of the Moon.
On the other hand, Ceres has a mass of 9,5 × 1020 kg, which represents a third of the total. Along with Vesta (9%), Pallas (7%) and Hygía (3%) that reaches more than half of the mass. The next three asteroids Davida (1,2%), Interamnia (1%) and Europa (0,9%) only add another 3% to the total mass. From here, the number of asteroids increases rapidly as their individual masses decrease.
Regarding the number of asteroids, this decreases markedly as the size increases. However, this follows a distribution of powers, since there are jumps for 5 and 100 km where more asteroids are found than expected according to a logarithmic distribution.
Four: Distribution of asteroids in the solar system
The term for near-Earth asteroids is also widely used by astronauts in such a way that they call it NEWS. This is the English acronym for Near-Earth Asteroids. The NEA are all those astronomical objects that have an orbit close to our planet Earth, in which it has been proven that they are not really comets. There are more than 10 known NEAs with these characteristics and with diameters ranging from one meter to the approximately 000 km of Ganymede.
Near-Earth asteroids larger than one kilometer are closer to 1000. Eros it was the first asteroid of this group to be discovered. However, much of these bodies are debris from extinct comets. Other NEAs are thought to originate in the asteroid belt where Jupiter's gravitational influence expels asteroids falling into the Kirkwood gaps into the inner solar system.
What contributes to the continuous supply of asteroids to the Jovian resonances is an effect that goes by the name of Yarkovsky. On the other hand, it is essential to highlight that the estimated duration of the NEA is a few million years.And its composition is comparable to that of main-belt asteroids or short-period comets. These asteroids, called NEA, are divided into three main groups according to the semi-major axis, perihelion and aphelion.
Asteroids Aton
There is a denomination of asteroids that have a semi-axis that is greater than one Astronomical Unit, they are called asteroids aton. The name is derived from the asteroid Atón, who gives the name to the group that composes. However, if they also do not cross Earth's orbit, they are called Apohele asteroids, Atira asteroids, or inner-Earth objects. Some asteroids in this group, such as Cruithne, have orbits similar to Earth's.
Apollo Asteroids
Another group of asteroids, are named after Apollo Asteroids. These have a semi-axis that is greater than or even greater than 1AU and cross the Earth's orbit. The Apollo asteroid gives its name to the group that is made up of more asteroids.
Asteroids Love
The group asteroids love, are those with a perihelion that is greater than the terrestrial aphelion and less than 1,3AU.
Potentially dangerous asteroids
On the other hand, asteroids are not always bearers of good news. There are also asteroids that turn out to be potentially dangerous, according to scientists. Astronomers call them PHAs, after their acronym for Potentially Hazardous Asteroids. Or what is the same potentially dangerous asteroidsThis group of asteroids are those that approach Earth at less than 0,05 AU and have an absolute magnitude that is less than 22.17. The largest of these bodies is Toutatis. Check out more information about hazardous asteroids.
Main belt asteroids
The main belt is nothing more than the one previously mentioned. That is, the asteroid belt. This region of the solar system is located between the orbits of Mars and Jupiter. This is where most of the asteroids form part of it, at distances between 2 and 3,5AU. For this reason this group is called main belt asteroids.
Specifically Ceres, Pallas, Vesta, Juno and Hygieia, make up more than half of the mass. However, the total mass of the belt is barely 4% of the mass of the Moon. With respect to asteroid belt formation, it can be said that its origin arises from the protosolar nebula, along with the rest of the solar system. On the other hand, the fragments of material contained in the belt region could have formed a planet.
However, gravitational disturbances from Jupiter, the most massive planet, caused the aforementioned fragments to collide with each other at high speeds and were unable to clump together. This resulted in the rocky remnant seen today. Another consequence of these disturbances are the Kirkwood hollows, which are areas where asteroids are not found due to orbital resonances with Jupiter causing their orbits to become unstable.
It is important to note that the asteroid belt is divided into different regions according to the boundaries marked by the Jovian resonances. However, not all authors agree. Most divide it into inner, outer, and middle or main belt proper, whose boundaries are the 4:1 and 2:1 resonances. Furthermore, according to these researchers, the main belt is divided into three zones designated by Roman numerals and bounded by the 3:1 and 5:2 resonances.
On the other hand, a last resonance, 7:3, marks an interruption in zone III. Some asteroids have orbits that are so eccentric that they cross that of Mars and in English, they are called Mars-crossing asteroids.
The four fundamental aspects of Asteroids help to know a little more about it and even about the changes in their denominations. Over the years, technology has collaborated quite a bit, however we have to wait for more details. What will the following results bring us about Asteroids? We don't know, but for now the universe is still a big space that continues to generate interest.
