How many planets are there in our solar system? Which planet is the largest? What kind of planet is a gas giant? In this article you’ll find answers to those questions and more!
Solar system is our little neighborhood in the Milky Way Galaxy with billions of celestial bodies that are gravitationally bound to the sun. Among the celestial bodies we have eight planets with several hundred moons orbiting them, as well as dwarf planets, asteroids, comets and many other smaller objects.
How many planets are there in the solar system?
There are eight (since 2006) planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The first four are rocky planets and the next four are gas giants. Each outer planet is surrounded by rings of cosmic dust.
In addition, there are five dwarf planets in the planetary system: Ceres, Pluto (until recently considered the ninth full-fledged planet), Haumea, Makemake and Eris. Six of the eight main planets and four of the five dwarf planets have natural satellites (moons).
Almost all planets are named after gods known from Roman mythology. Uranus owes its name to the Greek god of heaven: Ouranos.
Mercury – the smallest planet in the solar system
Mercury is the smallest and the closest planet to the sun in the solar system. Mercury is quite difficult to observe from Earth because of its location. Nevertheless, it is visible to the naked eye just after sunset or before sunrise. The first described observations of the smallest planet in the solar system are dated back to antiquity.
Mariner 10 is the first spacecraft to approach Mercury. The closest distance the Mariner probe came to Mercury is only 327 kilometers. About 2,500 photos of the planet’s surface were taken during the mission. Mariner 10 became the first artificial satellite of the first planet of the solar system. Its fuel supply has run out, but it is most likely orbiting the planet to this day.
Mercury has virtually no atmosphere. It also has no natural satellites. The surface of the planet with its numerous impact craters resembles the Moon. The surface temperature varies between -170 degrees and over 400 degrees Celsius. Mercury has a very large iron core, which makes it, despite its small size, a planet with one of the highest densities in the solar system.
Venus – the third brightest point in the sky
The second planet of the solar system, Venus is the brightest object seen in the Earth’s sky, after the Sun and Moon. Like Mercury, it is only visible before sunrise or just after sunset, but its brightness allows easy observation.
Due to its size, chemical composition and mass, it is often referred to as Earth’s sister (or twin planet). Unfortunately, the conditions on its surface do not encourage colonization. Atmospheric pressure is over ninety times greater than Earth’s.
The atmosphere consists almost entirely of carbon dioxide and sulfur. The surface temperature is extreme – over 400 degrees Celsius. Most of Venus’ surface is shaped by volcanic processes.
Due to its distance from Earth, Venus was the first planet to be set as the destination of a space mission. The Soviet Venera 3 probe reached the planet’s surface in 1966. Unfortunately, due to the failure of communication systems, the probe did not transmit any data to Earth. Venera 4, on the other hand, reached Venus a year later. The probe transferred to Earth a lot of surprising information about the nature of the planet, such as high temperature and the density of the atmosphere.
Earth – our home, third planet from the sun
Earth is the third planet from the sun and the fifth largest in the solar system. It is also the largest rocky planet. Earth is the only place in the universe known to house life. Our planet was formed about 4.5 billion years ago.
Later, the first living organisms appeared on Earth, which now form the biosphere. The Earth’s atmosphere is a gaseous shell mainly composed of nitrogen and oxygen. The Earth’s atmosphere protects us from ultraviolet radiation and provides optimal conditions for the maintenance of various forms of life. The hydrosphere is composed of all surface and ground waters. The lithosphere is the outer, rigid shell of the Earth.
Mars – Could there be life on a red planet?
Mars is the fourth planet in the Solar System and the last of the rocky planets. Its name comes from the name of the Roman god of war. In fact, the rusty color of Mars comes from iron oxides that coat the planet’s surface.
Although Venus is referred to as Earth’s twin planet, Mars has seen more favorable conditions for colonization, mainly lower surface temperatures and documented sources of groundwater (in the form of ice).
Mars has been explored by humans since 1965, when the Mariner 4 spacecraft made its first pass near the planet. Six years later, the American Mariner 9 entered its orbit, and a little later the Soviet Mars 3 landed on the surface of the Red Planet.
Soviet and American unmanned probes landed on Mars many times, conducting a series of studies of the atmosphere and lithosphere and, of course, looking for any form of life there. Currently, even astronomical observations are made from the surface of Mars.
Not so long ago (April 19, 2021) we witnessed the first controlled flight in the atmosphere of Mars by an Ingenuity drone that was placed there by the Perseverance rover. Each unmanned mission to Mars brings us closer to the first manned landing, which is planned for the 30s of the XXI century.
Jupiter – the largest planet of the Solar System
Jupiter is the fifth planet, counting from the Sun and the first of the so-called gas giants (otherwise known as Jupiter planets). Jupiter is the largest planet in our solar system – its mass is estimated to be more than two and a half times greater than that of all the other planets in the solar system combined.
Due to its size, Jupiter is the fourth brightest celestial body visible in Earth’s sky after the Sun, Moon and Venus. Jupiter is three-fourths hydrogen and one-fourth helium. This gas giant most likely has a solid rocky core. At least 79 natural satellites orbit it, the largest of which – Ganymede – is larger than Mercury.
To date, several research missions have been successfully dispatched to explore this heaviest planet in the solar system. The Pioneer and Voyager programs were designed to take the first photographs of the planet’s atmosphere.
The so-called Great Red Spot – a phenomenon observed on the surface of Jupiter even from Earth, which turned out to be a huge anticyclone that has been blowing on Jupiter for over 350 years. Man even managed to put two unmanned probes into the orbit of this gas giant: Galileo and Juno.
Saturn – the second largest planet after Jupiter in terms of mass and size
Another, sixth planet in the solar system and the second gas giant is Saturn. The hallmark of Saturn are the natural rings visible even from Earth, consisting mainly of ice and rock debris. It is the second largest planet in our system.
Saturn also has the most natural satellites in the planetary system. The planet has at least eighty-two moons. Saturn is assumed to be similar in structure to Jupiter – it consists mainly of hydrogen and helium, and a rocky core.
The first probe – Pioneer 11 – approached the surface of the planet as early as 1979. Another, Cassini, entered Saturn’s orbit in 2004. During this mission, the occurrence of thunderstorms on Saturn’s surface was observed, as well as the presence of hydrocarbon lakes and structures of extensive terrain, including lakes and mountains.
Uranus – the only Greek god in the solar system
The seventh planet of the solar system is Uranus. Although it is referred to as a gas giant, and its chemical composition is mainly hydrogen and helium, Uranus also contains ice fragments (ammonia, water, methane and other hydrocarbons).
Hence, Uranus is sometimes classified in another group of planets, the so-called ice giants. An interesting fact is that the planet’s axis of rotation is close to the plane of its orbit, which means that Uranus’ poles are located where the equator of other planets is usually located. It was only discovered at the end of the 18th century and was initially confused with a star or comet. The outer structure of the planet is uniform – no weather activity can be observed on its surface.
So far, only the Voyager 2 unmanned aerial vehicle has come close to the atmosphere of Uranus. No new missions in this direction are planned.
Neptune – another gas giant, Uranus’ twin
Eighth planet of the solar system is Neptune and is known as Uranus’ twin brother because of its size and the presence of ice in the atmosphere. Unlike its galactic neighbor, Neptune has distinct weather patterns formed by the strongest winds observed in our planetary system.
Its speed is estimated at 2,100 km/h. Neptune, due to its distance from the Sun, is one of the coldest places in the Solar System – the temperature on the surface is often below -220 degrees Celsius. Voyager 2 has moved closer to Neptune and its largest moon, Triton.
The ninth planet? Pluto and other dwarf planets
Dwarf planets are relatively new to astronomy – the term was only introduced in 2006. A dwarf planet is defined as a celestial body with a shape similar to a spherical one, which is in the orbit of the Sun, which is not a satellite of another celestial body. However, their mass has to be much lower than a traditional planet.
Pluto was discovered in 1930. Until 2006, it was considered the ninth planet of the Solar System, just until the term “dwarf planets” was introduced. To date, five objects in our planetary system have been identified as dwarf planets – Ceres, Pluto, Haumea, Makemake and Eris.
Not only planets – what else is there in our solar system?
The solar system is not only a group of eight planets and five dwarf planets – the structure of the solar system is much more complex. In orbit behind the four rocky planets (between the orbits of Mars and Jupiter) is the main asteroid belt with celestial bodies such as Ceres, Westa, Pallas and Hygiea.
The asteroid system is so rare that many space probes have passed through it without encountering any object en route. In turn, behind the orbit of Neptune is the Kuiper Belt – a system of celestial bodies similar to the main asteroid belt, but definitely more massive.
There are at least three dwarf planets orbiting there: Pluto, Haumea and Makemake. By 2020, two thousand bodies were discovered in it, but it is assumed that there are at least seventy thousand objects in the belt with fairly stable orbits.
Behind Neptune’s orbit, near the Kuiper Belt, there is the so-called scattered disk with many celestial bodies in orbits whose regularity is disturbed by the gravity of the gas giants. Some publications link the Kuiper Belt with a scattered disk, and it is not fully known how to classify this distant part of the solar system.
The outer parts of the solar system are defined by the range of the so-called solar wind. The solar wind is a stream of plasma (protons, electrons, and alpha particles) emitted by the sun relatively uniformly in all directions.
The space filled by the solar wind is not a perfect sphere – the shape of the interaction is deformed by the gravity force of individual planets, mainly gas giants. The scattered disk ends with the so-called heliopause – an imaginary layer where the solar wind balances with the force of interstellar matter.
The outer part of the solar system is the The Oort Cloud. It’is a remnant of the formation of our planetary system. That is a hypothetical cloud of cosmic particles that has never been explored before. Its distance from the Sun is a thousand times greater than that of the Kuiper Belt from our central star.
The Oort Cloud is probably the place where many long-period comets are “born”, which have been knocked out of their original orbit. Meanwhile, short-period comets most often come from the Kuiper Belt or scattered disk.
What other surprises do you think our solar system hides? Or maybe – using, for example, binoculars or a telescope – you observed the Moon or other celestial bodies? Let us know in the comments!