Which planet is the seventh in the solar system. Solar system. Planets of the solar system. “Look, what poems came out...”
The number of galaxies in the Universe is largely unknown to people, with astronomers suggesting there could be an infinite number of them. In our galaxy, the Milky Way, scientists estimate that there are about 100 billion planets, most of which are in the orbit of stars. In the recent past, astronomers have discovered hundreds of planets in our galaxy, some of which exhibit characteristics of our Earth, suggesting they could support life. Our Solar System consists of the Sun, eight planets and their moons (satellites), and various small cosmic bodies. The solar system long included nine planets until Pluto was stripped of its rank in 2006 because it did not meet the necessary criteria. It was discovered that Pluto is part of a group of six space objects that orbit the Kuiper Belt and is not the largest of them.
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Mercury
Mercury is the closest planet to the Sun; it is also the smallest of all eight planets. Over the course of 88 days, Mercury completes a full revolution around the Sun. It is a rocky planet with an equatorial radius of 2439.7±1.0 km and a density of 5427 g/cm³, making it the second densest planet in the Solar System. Mercury has no atmosphere and temperatures range from 448ºC during the day to -170ºC during the night. Its orbit is oval and it is one of the planets that can be seen from Earth.
Venus
Venus is the second planet from the Sun. It takes 224.7 days to complete a revolution, and its rotation period on its axis is about 243 days (the slowest rotation of any planet in the solar system). Venus is the hottest planet with a surface temperature of about 467º C, as its atmosphere is thick and retains heat well. It is very bright in the morning and evening, making it highly visible in certain regions of the Earth. It is the closest planet to us, and also the first to be visited by an Earth probe (Mariner 2) in 1962. The dense hot atmosphere makes Venus inaccessible to humans.
Earth
Planet Earth is home to humans and is considered the only planet known to have life. It completes its orbit around the Sun in 365,256 days, covering a distance of approximately 940 million km. The Earth is located about 150 million km from the Sun and is the third planet in our system; According to scientists, its formation began 4.54 billion years ago. The total area of the Earth is more than 510 million km², 71% of which is covered by water, and the remaining 29% is land. The Earth's atmosphere protects life from outer space, harmful radiation and controls the weather. It is the densest planet in the solar system.
Mars
Mars, also known as the "red planet", is the fourth planet in our solar system and the second smallest. It has a solid surface, like Earth, but its atmosphere is relatively thin. Mars is half the size of Earth and is on average 228 million km from the Sun; it completes its orbit around the Sun in 779.96 days. It is clearly visible from Earth at night due to its bright surface. Liquid water is not found on the surface of the planet due to low atmospheric pressure. Researchers are studying the possibility of life on Mars. Scientists believe that the ice caps at the planet's poles are water, and the ice at the south pole could fill the planet's surface to a depth of 11 m if it melts.
Jupiter
Jupiter is the fifth and largest planet in the solar system. Its mass is 2.5 times the total mass of other planets. Jupiter is a gaseous planet with no solid surface, although researchers believe its core is solid. It has a diameter of 142,984 km at the equator and is so large that it can contain all the planets of the solar system or 1,300 earths. It is predominantly composed of hydrogen and helium. Jupiter's atmosphere is dense, with wind speeds averaging 550 km per hour, which is twice the speed of a Category 5 hurricane on Earth. The planet has three rings of dust particles, but they are difficult to see. It takes Jupiter 12 Earth years to complete a full revolution around the Sun.
Saturn
Saturn is the second largest planet after Jupiter and the sixth in the solar system. It is a gas giant, just like Jupiter, but with nine continuous rings. Saturn is considered the most beautiful planet in our system and is composed of hydrogen and helium. Its diameter is nine times that of Earth, its volume is comparable to that of 763.5 Earths, and its surface is equal to 83 Earths. However, Saturn's mass is only one-eighth that of our planet. Saturn has nearly 150 moons, 53 of which are named, 62 identified as having orbits, and the remaining moons located in the planet's rings.
Uranus
Uranus is the seventh planet and the third largest in the solar system. Its surface consists of frozen matter and is therefore considered an ice giant. However, Uranus' atmosphere also includes hydrogen and helium, along with other "ices" such as methane, ammonia and water. Although it is not the farthest planet from the Sun, it is one of the coldest with atmospheric temperatures reaching -224 C, as it is the only planet in the solar system that does not generate heat from its core. The average distance of Uranus from the Sun is about 2.8 billion km.
Neptune
Neptune is the eighth and farthest planet from the Sun. It was first thought to be a fixed star by Galileo, who used mathematical predictions to discover it rather than the usual telescope method. The average distance from Neptune to the Sun is 4.5 billion km, and a complete revolution around our star occurs in 164.8 years. Neptune completed its first orbit in 2011, having been discovered in 1846. It has 14 known moons, the largest of which is Triton. The atmosphere is dominated by hydrogen and helium. It is the windiest planet in the solar system, with an average wind speed nine times that of Earth. NASA recently discovered that Neptune has rivers and lakes of liquid methane.
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Quick answer: 8 planets.
The solar system is a planetary system that includes the central star, which is the Sun, as well as all other natural space objects, which in turn revolve around the Sun.
Interestingly, most of the total mass of the solar system is accounted for by itself, while the rest is accounted for by 8 planets. Yes, yes, there are 8 planets in the solar system, and not 9, as some people believe. Why do they think so? One reason is that they mistake the Sun for another planet, but in fact it is the only star included in the solar system. But in reality everything is simpler - Pluto was previously considered a planet, but is now considered a dwarf planet.
Let's begin the review of the planets, starting with the one closest to the Sun.
Mercury
This planet was named after the ancient Roman god of trade - the fleet-footed Mercury. The fact is that it moves much faster than other planets.
Mercury completely revolves around the Sun in 88 Earth days, while the duration of one sidereal day on Mercury is 58.65 Earth days.
Relatively little is known about the planet, and one of the reasons is that Mercury is too close to the Sun.
Venus
Venus is the second so-called inner planet of the solar system, which was named after the goddess of love, Venus. It is worth noting that this is the only planet that received its name in honor of a female deity, rather than a male one.
Venus is very similar to Earth, not only in size, but also in composition and even gravity.
It is believed that Venus once had many oceans similar to the ones we have. However, some time ago the planet heated up so much that all the water evaporated, leaving behind only rocks. Water vapor was carried into outer space.
Earth
The third planet is Earth. It is the largest planet among the terrestrial planets.
It was formed approximately 4.5 billion years ago, after which it was almost immediately joined by its only satellite, which is the Moon. It is believed that life on Earth appeared about 3.9 billion years ago and over time its biosphere began to change for the better, which allowed the formation of the ozone layer, increased growth of aerobic organisms, etc. All this, among other things, allows us to exist now.
Mars
Mars closes the four terrestrial planets. The planet is named after the ancient Roman god of war, Mars. This planet is also called red because its surface has a reddish tint due to iron oxide.
Mars has surface pressure 160 times less than Earth's. On the surface there are craters similar to those that can be seen on the Moon. There are also volcanoes, deserts, valleys and even ice caps.
Mars has two satellites: Deimos and Phobos.
Jupiter
It is the fifth planet from the Sun and the first among the giant planets. By the way, it is the largest in the solar system, which received its name in honor of the ancient Roman supreme god of thunder.
Jupiter has been known for a long time, which is reflected in ancient myths and legends. Has a very large number of satellites - 67 to be exact. Interestingly, some of them were discovered several centuries ago. Thus, Galileo Galilei himself discovered 4 satellites in 1610.
Sometimes Jupiter can be seen with the naked eye, as was the case in 2010.
Saturn
Saturn is the second largest planet in the solar system. It was named after the Roman god of agriculture.
It is known that Saturn consists of hydrogen with signs of water, helium, ammonia, methane and other heavy elements. An unusual wind speed was observed on the planet - about 1800 kilometers per hour.
Saturn has prominent rings that are mostly made of ice, dust, and other elements. Saturn also has 63 satellites, one of which, Titan, is larger than even Mercury.
Uranus
The seventh planet in terms of distance from the Sun. It was discovered relatively recently (in 1781) by William Herschel and was named after the god of the sky.
Uranus is the first planet to be discovered using a telescope between the Middle Ages and modern times. Interestingly, although the planet can sometimes be seen with the naked eye, before its discovery it was generally believed that it was a dim star.
Uranus has a lot of ice but no metallic hydrogen. The planet's atmosphere is composed of helium and hydrogen, as well as methane.
Uranus has a complex ring system and 27 satellites.
Neptune
Finally, we have reached the eighth and last planet of the solar system. The planet is named after the Roman god of the seas.
Neptune was discovered in 1846, and, interestingly, not through observations, but thanks to mathematical calculations. Initially, only one of its satellites was discovered, although the remaining 13 were not known until the 20th century.
Neptune's atmosphere consists of hydrogen, helium and possibly nitrogen. The strongest winds rage here, the speed of which reaches a fantastic 2100 km/h. In the upper layers of the atmosphere the temperature is about 220°C.
Neptune has a poorly developed ring system.
All planets are located in a certain sequence, the distances between their orbits increase as the planets move away from the Sun.
Composition of the Solar System
Sun
Concentrated 99.9% of the total mass of the system. The star is composed primarily of hydrogen and helium. Essentially, this is a giant thermonuclear reactor. Temperature is about 6000 °C. But the luminary exceeds 10,000,000 °C.
At a speed of 250 km/sec, our star rushes through space around the center, which is “only” 26,000 light years away. And one revolution takes about 180 million years.
Planets and their satellites
Earth group.
The closest to the Sun, but also the smallest of the planets. It revolves around itself very slowly, making only one and a half revolutions around its axis for a full revolution around the luminary. The planet has neither an atmosphere nor satellites, during the day it heats up to +430 °C, and at night it cools to -180 °C.
The most romantic and closest planet to Earth is also not suitable for habitation. It is tightly wrapped in a thick blanket of carbon dioxide clouds, and at temperatures up to + 475 ° C, it has a pressure at the surface dotted with craters of over 90 atmospheres. Venus is very close to Earth in size and mass.
Similar in structure to our planet. Its radius is half that of Earth, and its mass is an order of magnitude less. It would be possible to live here, but the lack of water and atmosphere prevents this. The Martian year is twice as long as the Earth's, but the days are almost the same length. Mars is richer than the first two planets, having two satellites: Phobos and Deimos, translated from Greek as “fear” and “terror”. These are small blocks of stone, very similar to asteroids.
Giant planets.
The largest gas giant planet. If its mass were several tens of times greater, it could really become a star. A day on the planet lasts about 10 hours, and a year passes in 12 Earth hours. Jupiter, like Saturn and Uranus, has a ring system. He has four of them, but they are not very pronounced; from afar you might not even notice them. But the planet has more than 60 satellites.
This is the most ringed planet the Solar System has. Saturn also has a feature that other planets do not have. This is its density. It is less than one, and it turns out that if you find a huge ocean somewhere and throw this planet into it, it will not drown. At this time, more than 60 satellites of this giant have been discovered. The main ones are Titan, Dione, Tethys. Saturn is similar to Jupiter in the structure of its atmosphere.
The peculiarity of this planet, which appears to the observer in blue-green tones, is in its rotation. The planet's rotation axis is almost parallel to the ecliptic plane. In layman's terms, Uranus lies on its side. But this did not stop him from acquiring 13 rings and 27 satellites, the most famous of which are Oberon, Titania, Ariel, and Umbriel.
Just like Uranus, Neptune is made of gas, including water, ammonia and methane. The latter, concentrating in the atmosphere, gives the planet a blue color. The planet has 5 rings and 13 satellites. The main ones: Proteus, Larissa, Nereid.
The largest among dwarf planets. It consists of a rocky core covered with a layer of ice. Only in 2015 did a spacecraft fly to Pluto and take detailed photographs. His main companion is Charon.
Small objects
Kuiper Belt. Part of our planetary system from 30 to 50 AU. e. The mass of small bodies and ice is concentrated here. They consist of methane, ammonia and water, but there are objects that include rocks and metals.
The orbits of these stone or metal blocks are mainly located near the ecliptic plane. The paths of some asteroids intersect with the Earth's orbit. And, although the probability of an unwanted meeting is negligible, but... 65 million years ago it probably still took place.
According to legend, a certain planet Phaeton, peacefully revolving around the star, was torn to shreds by Jupiter’s gravity. And it turned out to be a beautiful asteroid belt. In fact, science does not confirm this.
If you translate this word from Greek, you get “long-haired.” And so it is. When the icy wanderer approaches the Sun, it spreads a long tail of evaporating gases over hundreds of millions of kilometers. The comet also has a head, consisting of a nucleus and a coma. The core is an ice block made of frozen gases with additions of silicates and metal particles. It is possible that some organic matter is also present. Coma is the gas and dust environment of a comet.
Jan Oort, back in 1950, proposed the existence of a cloud filled with objects made of icy ammonia, methane and water. It has not yet been proven, but it is possible that the cloud starts from 2 - 5 thousand AU, extending to 50 thousand AU. e. Most comets come from the Oort cloud.
Earth's place in the solar system
It is impossible to imagine a more successful position than what he occupies. This part of our galaxy is quite calm. The sun provides a constant, uniform glow. It releases exactly as much heat, radiation and energy as is required for the origin and development of life. The Earth itself seemed to have been thought out in advance. Ideal atmospheric composition and geological structure. The required background radiation and temperature conditions. The presence of water with its amazing properties. The presence of exactly such a mass and at such a distance as required. There are many more coincidences that are crucial for a favorable life on the planet. And the violation of almost any of them would make the emergence and existence of life unlikely.
System stability
The revolution of the planets around the Sun occurs in one (direct) direction. The orbits of the planets are practically circular, and their planes are close to the Laplace plane. This is the main plane of the solar system. Our life is subject to the laws of mechanics, and the solar system is no exception. The planets are connected to each other by the law of universal gravitation. Based on the absence of friction in interstellar space, we can confidently assume that the motion of the planets relative to each other will not change. At least in the next million years. Many scientists have tried to calculate the future of the planets in our system. But everyone - and even Einstein - got one thing: the planets of the solar system will always be stable.
Some interesting facts
- Temperature of the solar corona. The temperature near the Sun is higher than on its surface. This mystery has not yet been solved. Perhaps the magnetic forces of the star's atmosphere are at work.
- Atmosphere of Titan. It is the only one of all the planetary satellites that has an atmosphere. And it consists mainly of nitrogen. Almost like earthly.
- It remains a mystery why the activity of the Sun occurs with a certain periodicity and time.
Our planetary system has been studied successfully for a long time. The Moon, Venus, Mars, Mercury, Jupiter and Saturn are under constant surveillance. Traces of people and all-terrain vehicles are left on our satellite. Autonomous rovers roam around Mars, transmitting valuable information. The legendary Voyager has already flown through the entire solar system, crossing its boundaries. Even a comet. And a manned trip to Mars is already being prepared.
We are incredibly lucky to have settled in such a place in the Universe. Although no one has yet proven whether there are other worlds. But we still know so little about our system of beautiful planets. And now we are calm and businesslike. Or, perhaps, a pebble has already been released from the Oort cloud and is flying directly towards Jupiter. Or, nevertheless, this time to us?
How many planets are there in the solar system?
The idea of what a planet is and how many there are in the solar system has changed over the centuries. Ancient astronomers did not have telescopes, and the only key characteristic to distinguish planets from other celestial bodies was that they moved across the sky relative to other stars. For them there were fixed stars and wandering stars - planets. Sometimes the Sun and Moon were also considered planets. The very word “planet”, which translated from ancient Greek means “wandering”, “wandering”, allowed this.
The geocentric system of the world assumed that at the center of the universe there is a stationary Earth, and the Sun, Moon and planets revolve around it. But Copernicus placed the Sun at the center of the world. After which it turned out that the Earth, like other planets, also revolves around it. And if so, then the Earth began to be considered a planet, because it was no longer stationary, but moved in a circle around the Sun.
After the final approval of the Copernican heliocentric system, the Moon remained the only satellite orbiting our planet. But in 1610, the Galilean satellites of Jupiter were discovered. And then they discovered satellites on Saturn. At first, many different terms were used to refer to planetary satellites: they were called moons, stars, secondary planets, and simply planets. But over time, the term “satellite” nevertheless replaced all others.
The number of planets began to increase again by the mid-19th century. Planet status was assigned to any object orbiting the Sun, with the exception of comets. The list of planets was expanded to include Ceres, Pallas, Vesta and Juno. And by this time, in addition to the planets known since ancient times, Uranus was also added. And in 1846 - Neptune. Since Ceres and similar objects were small in comparison with previously known planets and were located in one region of the solar system, later called the asteroid belt, they were decided to be separated into one separate group and called asteroids.
The growth in the number of planets stopped with the discovery of Pluto in 1930. It became the 9th planet of the solar system. It was in this form that she was familiar to all of us. But by the end of the last century, the possibilities of astronomy had increased. And we are on the verge of discovering new planets beyond the orbit of Pluto. But there was no increase in the number of planets. The astronomical community, faced with the dilemma of assigning planetary status to newly discovered celestial bodies or depriving Pluto of such status, chose the latter. In general terms, the situation of the 19th century was repeated. For newly discovered bodies (today these are Eris, Haumea, Makemake) and for the previously discovered Pluto and Ceres, a new category was introduced - dwarf planets.
Thus, today there are eight planets in the solar system, five dwarf planets. Among the eight “large” planets, four - Mercury, Venus, Earth and Mars - are called terrestrial planets, and Jupiter, Saturn, Uranus and Neptune are called giant planets. The latter are also called gas giants, two of which - Uranus and Neptune - are classified as ice giants.
There are several thousand objects called minor planets (there is such an unofficial concept). The Minor Planet Catalog is maintained by the Minor Planet Center at the Smithsonian Astrophysical Observatory. Among them there are many remarkable objects. These are, for example, such dwarf planet candidates as Quaoar and Sedna.
But we are talking about open planets. The size of our solar system allows us to accommodate a larger number of planets. In any case, Michael Brown, the same “killer” of Pluto, is sure that there is another, ninth planet in the solar system.
Why Pluto is not like other planets
Pluto has always been different. It is small and its orbit is different from other planets. But the youngest in the family was forgiven for this. So why didn’t they forgive Pluto when they deprived him of his honorary status?
Pluto/© NASA
So, the first condition in order to be considered a planet is that the celestial body must be in orbit around the Sun. This condition excludes the satellites of planets from the scope of the definition, although some of them are quite comparable in size to planets, for example, Jupiter’s satellite Ganymede, which has a diameter exceeding the diameter of Mercury. Second, the celestial body must have sufficient gravity to have a spherical shape. Formless objects, such as the asteroids Pallas, Vesta and Juno, disappear. But their neighbor in the asteroid belt, Ceres, is still holding on, which, although the smallest of the dwarf planets, is quite massive, which allowed it to take on the shape of a ball. And finally, the third condition is that near the orbit there must be space free from other bodies.
Neither Ceres, located in the asteroid belt, nor Pluto, located in the Kuiper belt, were able to clear the vicinity of their orbit from other objects.
At the same time, the list of conditions did not include the requirements of a small eccentricity of the orbit (circular orbit) and a small inclination of the orbit to the ecliptic plane. This may be due to the fact that the orbit of the hypothetical new ninth planet will not meet these conditions.
Ecliptic and zodiac
One of the key characteristics of any celestial body is the inclination of its orbit. For planets and other bodies orbiting the Sun, the inclination of the orbit, or more precisely, the orbital plane to the ecliptic plane, is taken into account. This allows us to understand how a celestial body moves in the solar system.
The plane of the ecliptic in the solar system is the plane of the Earth's orbit. If you know the amount of tilt, you can imagine where to look for an object in the sky.
The orbits of all planets lie near the ecliptic plane. Mercury stands out a little, its maximum angle of inclination to the ecliptic is 7.01°. For comparison, the orbital inclination of Pluto, once the ninth planet, is 17.14°.
At the dawn of the solar system, planets formed from a protoplanetary disk of gas and dust. This is how scientists explain why all the planets revolve around the Sun in the same plane. But there are celestial bodies in our system whose inclination angle is even greater, but more about them later.
Where the ecliptic is, there is the zodiac. The ecliptic itself is a large circle of the celestial sphere along which the visible annual movement of the Sun occurs. If we could see the stars and constellations during the day, then throughout the year we would observe the Sun in one of the zodiac constellations. In May–June, for example, the Sun is in the constellation Gemini. Uranus will be in the constellation Pisces this June, and Neptune will spend the month in Aquarius. Neither the Sun nor the planets go beyond the “zodiacal zone”.
It would seem that if everything in the Solar System was formed from a protoplanetary disk, then the orbits of all bodies should lie in the same plane, but no. The inclination of the orbit of comet Hale-Bopp, which arrived at us from the Oort cloud at the end of the last century, is 89.43°. In 1997, it approached the Sun almost perpendicular to the ecliptic plane.
Sedna, Voyager and the edge of the solar system
59 years have passed since the launch of the first artificial Earth satellite. During this time, we have achieved a lot in astronautics. But the dreams of science fiction writers about interstellar flights have not yet come true. Even going beyond the solar system is questionable. On the one hand, the speeds of our spacecraft are unacceptably low, on the other, it is not entirely clear where this boundary is.
Voyager 1/©Wikipedia
The Voyager 1 space probe is the furthest human-made object from Earth. Launched in 1977 to study Jupiter and Saturn, in 39 years it moved 135 astronomical units from the Sun. In earthly measures of length, this is more than 20 billion kilometers. But for measuring distance within the solar system, terrestrial measures are not entirely convenient.
Distances in the Solar System and systems of other stars are measured in astronomical units. One astronomical unit is approximately equal to the average distance from the Earth to the Sun. This is almost 149.5 million kilometers. Thus, Voyager 1 moved away from the Sun to a distance equal to 135 distances from the Sun to our planet.
For example, the average distance from Mars to the Sun is 1.52 AU. e., from Neptune to the Sun – 30.1 a. e. The orbit of Pluto, in contrast to the almost circular orbits of the “large” planets, has a greater eccentricity, that is, it is an ellipse. For such celestial bodies, indicating average distances does not make much sense. At perihelion (the closest point in its orbit to the Sun), Pluto approaches our star at a distance of 29.7 AU. That is, at aphelion (the farthest point from the Sun) it moves away by 49.3 AU. e.
But these distances are nothing compared to the orbital characteristics of Sedna, a trans-Neptunian object, another candidate for the title of dwarf planet. Its orbit is even more elongated than Pluto's. The point of the orbit closest to the Sun is at a distance of 76 AU. e. In this case, the farthest point of the orbit is at a distance of 900 a. e. - almost 7 times further than Voyager 1 is now.
Previously, several times there were reports that Voyager 1 went beyond the solar system. Finally, NASA clarified the issue - the spacecraft entered interstellar space, but it did not leave the solar system. And therefore, they are not the same thing.
Voyager 1 reached the heliopause, the boundary of the heliosphere, the place where the solar wind finally slows down. But the boundary of the Solar system, according to scientists, should be considered the place where the gravitational forces of the Sun will be equal to zero. It will take the probe another 300 years to reach such a border. For the Sun, such a boundary, according to modern calculations, is located at a distance of approximately 2 light years. Within these limits there is, for example, the Oort cloud, from where the already mentioned comet Hale-Bopp flew to us.
Nemesis – a hypothetical companion of the Sun
But even beyond the Oort cloud, surprises can await us. We are talking about Nemesis - a hypothetical star, a possible and as yet undiscovered companion of the Sun. Maybe there is no star, of course. But in the vicinity of the Sun, about half of the stars are double, there is a high probability that the Sun is also part of a double star system.
The distance to Nemesis, if it exists, of course, is 50–100 thousand astronomical units. This is, however, an order of magnitude further than the extreme point of Sedna's orbit. It is worth noting that Michael Brown, its discoverer, when explaining such an extended orbit of Sedna, proposes as one of the hypotheses the influence of gravity of an as yet undiscovered large planet beyond the orbit of Neptune. But astronomer Walter Cruttenden expresses the opinion that it was the yet undiscovered star Nemesis that influenced the orbit of the small planet.
But if there is a star so close to us, then why haven’t we discovered it yet? This is explained simply. There are different stars, and not all of them are bright enough. Scientists searching for Nemesis suggest that this mysterious star could be a brown, red or white dwarf. By the way, the Sun is considered a yellow dwarf.
We are accustomed to the fact that stars are such luminous giants in the cosmic abyss. Even giant planets such as Jupiter and Saturn look very small in comparison. But those stars that belong to the above classes are by no means like that. White dwarfs are similar in size to our planet. Brown dwarfs are comparable in size to Jupiter.
Due to their small size and very low luminosity, such stars are difficult to detect, and if Nemesis exists, then this is one of the reasons that we have not found it yet. The question arises: how does the small and dim hypothetical Nemesis and similar known stars, and stars in general, differ from planets?
In the depths of stars, unlike planets, thermonuclear fusion reactions occur (or have occurred previously). And to start a thermonuclear reaction you need a significant mass. So, according to some estimates, Jupiter, which consists of hydrogen and helium, the same elements as stars, in order to become a star, needs to increase its mass by 47 times. Let us add that if there is a thermonuclear reaction, then there is luminosity and significant temperatures, which the planets do not have.
On a clear night, when light interference is not a major factor, the sky looks spectacular with a huge number of stars open to view. But, of course, we can only see a small fraction of the stars that actually exist in our Galaxy. What's even more amazing is that most of them have their own planetary system. The question arises, how many exoplanets are there? There must be billions of extraterrestrial worlds in our Galaxy alone!
So let's assume that the eight planets that exist within the solar system represent the average. The next step is to multiply this number by the number of stars that exist within the Milky Way. The actual number of stars in our Galaxy is a matter of some debate. Essentially, astronomers are forced to make rough estimates because we cannot view the Milky Way from the outside. And given that it is in the shape of a barred spiral, the galactic disk is the most difficult to study due to the interference of light from its many stars. As a result, the estimate is based on calculations of the mass of our Galaxy, as well as the mass fraction of stars in it. From this data, scientists estimate that the Milky Way contains between 100 and 400 billion stars.
Thus, the Milky Way galaxy could have between 800 billion and 3.2 trillion planets. However, in order to determine how many of them are habitable, we must consider the number of exoplanets studied so far.
As of October 13, 2016, astronomers have confirmed the presence of 3,397 exoplanets out of 4,696 potential candidates that were discovered between 2009 and 2015. Some of these planets were observed directly through direct imaging. However, the vast majority have been detected indirectly using the radial velocity or transit method.
The histogram shows the dynamics of exoplanet discovery by year. Credit: NASA Ames/W. Stenzel, Princeton/T. Morton
During its initial 4-year mission, the Kepler space telescope observed about 150,000 stars, which were mostly M-class stars, also known as red dwarfs. When Kepler entered a new phase of the K2 mission in November 2013, it shifted its focus to studying K- and G-class stars, which are almost as bright and hot as the Sun.
According to a recent study conducted by NASA Ames Research Center, Kepler found that about 24% of M-class stars may have potentially habitable planets comparable in size to Earth (those that are no more than 1. 6 times the radius of the Earth). Based on the number of M-class stars, there may be about 10 billion potentially habitable, Earth-like worlds in our Galaxy.
In addition, analysis of the K2 results suggests that about one quarter of large stars may also have Earth-like planets orbiting within habitable zones. Thus, it can be estimated that there are literally tens of billions of planets potentially suitable for the development of life in the Milky Way alone.
In the coming years, the James Webb and TESS space telescope missions will be able to detect smaller planets orbiting dim stars, and perhaps even determine whether any of them harbor life. Once these new missions get underway, we will have more accurate estimates of the size and number of planets that exist in our Galaxy. Until then, their estimated number is encouraging: the chances of extraterrestrial intelligence are very high!
