The solar system is a planetary system, in which the Earth rotates tirelessly. The solar system itself revolves in the galaxy, with planets and a star within it. It would even be quite unique.
At school, everyone learns the names of the planets that make up the solar system — often with great help from mnemonic devices to remember their order. But its structure and composition have not yet unveiled all their mysteries. Scientists continue to study it, which contains our precious home, the Earth.
What is the solar system?
The solar system is a collection of celestial objects. It is a planetary system, composed of bodies like planets, asteroids and comets, orbiting around a star, the Sun.
The planets are linked to the Sun by gravity. The same goes for dwarf planets, like Pluto, or the moons.
What are the planets of the solar system?
The 8 known planets of the solar system are:Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
There are planets outside our solar system — they even outnumber the number of stars visible at night. Most of the hundreds of billions of stars in our galaxy, the Milky Way, have their own planets. We then speak of exoplanets.
How big are the planets in the solar system?
Here is the diameter (at the equator) of each of the planets in the solar system.
| Diameter in kilometers | Size relative to Earth | |
| Mercury | 4,879 | 2.6 times smaller |
| Venus | 12 104 | 1.1 times smaller |
| Earth | 12,742 | x |
| March | 6,779 | 1.9 times smaller |
| Jupiter | 139,822 | 11 times bigger |
| Saturn | 116,464 | 9.1 times bigger |
| Uranus | 50,724 | 4 times bigger |
| Neptune | 49,244 | 3.9 times bigger |
What is the most extreme planet in the solar system?
The hottest planet in the solar system is undoubtedly Venus. With its 462° C on the surface, the neighbor of the Earth is quite infernal and extreme. One might be surprised that Mercury is less hot than Venus, while it is closer to the Sun.
But that would be to forget that Venus has a thick atmosphere, unlike Mercury: this envelope rich in carbon dioxide and clouds of sulfuric acid retains heat and causes a greenhouse effect.
Is there a ninth planet in the solar system?
This is only a hypothesis: a ninth planet located beyond the orbit of Neptune, Planet Nine, would remain to be discovered in the solar system. But, the existence of this star has never been confirmed: for the time being, it is only a scenario that would explain the orbits of certain objects in the Kuiper belt (a reservoir of frozen bodies at the bottom of the solar system). Not all scientists agree on the hypothesis of a ninth planet.
Which planets in the solar system can we see with the naked eye?
Some planets are visible without an astronomical instrument: this is the case of Mercury, Venus, Mars, Jupiter and Saturn – depending on the time of year, the position of the observer on Earth and the weather.
How many moons are there in the solar system?
There are more than 200 known moons in the solar system: NASA lists 214 exactly. The Earth has only one, soberly baptized the Moon. All the planets have them, except Mercury and Venus, which do not have a moon. Dwarf planets, like Pluto, as well as many asteroids, also have moons.
The planets with the most moons are, in order, Jupiter then Saturn. The first has 92 moons and the second 83.
How old is the solar system?
The solar system was formed 4.5 billion years ago.
How was the solar system formed?
He was born from a dense cloud of interstellar matter. The collapse of this cloud led to the formation of a solar nebula. The matter was attracted towards the center under the effect of gravity: during its birth, the Sun collected 99% of the available matter.
The rest of the matter also clumped together to form objects, such as planets, moons and dwarf planets. Residues that could not be assembled remained, especially in the asteroid belt, becomingasteroids, comets, meteoroids.
When we collect meteorites on Earth, we are collecting one of those precious remnants of the formation of the solar system.
Is the solar system unique?
The solar system is just one of many planetary systems that exist, consisting of a star with planets orbiting it. Over 3,200 stars with planets revolving around them have been discovered. But that does not prevent us from asking ourselves: is the configuration of our system rare, or rather banal, in the Universe?
Work on planetary systems tends to show a wide variety of possible structures in our galaxy. We could expect to often find a structure as we know it, with rocky and dense planets close to the star, and more distant gas giant planets. However, the discovery of more and more exoplanets seems to show that our solar system is more of an exception than a norm.
Why is the solar system split in two?
It is quite easy to notice this by observing a diagram of the solar system: it seems to be cut in two. A sort of “gap” between the orbits of Mars and Jupiter divides the small rocky planets on the one hand, and the large gaseous planets on the other. These two sets are located on either side of the asteroid belt.
Why this structure? Scientists are still trying to figure out what exactly happened. What we can remember is that this arrangement is linked to the way in which the system was formed. In the areas closer to the Sun, only the rocky material could resist the significant heat, in the youth of the solar system. This is why Mercury, Venus, Earth and Mars are telluric planets, with a solid surface. Materials like ice, liquid, and gas instead took up residence in the outer areas of the solar system, giving rise to Jupiter, Saturn, Uranus, and Neptune.
How far does the solar system extend?
The solar system has no border, like a tangible object. So, we can try to define its border as up to where the influence of the Sun extends. But, even so, it is not precise enough, since it is necessary to mention what influence we are talking about: its light, its gravity, its magnetic field, its solar wind?
We could also consider the planets, and decide that the solar system ends where Neptune and the Kuiper belt are (composed of icy asteroids, beyond the orbit of Neptune, and located at a distance between 30 and 1,000 astronomical units of the Sun; one astronomical unit represents the Sun-Earth distance, 150 million kilometers).
If we take as a criterion the gravitational influence of the Sun, the border would rather be located at the level of the Oort cloud. That is, well beyond the orbit of the planets and the Kuiper belt (between 2,000 and 100,000 astronomical units away from the Sun).
Why is it called the solar system?
There are many planetary systems like ours throughout the Universe, with planets orbiting a star. Ours was named solar system to refer to the name of our star, coming from the Latin “ ground, ground “. Everything related to the Sun is therefore called… solar.
Where is the solar system located in the Milky Way?
The solar system is not at the center of the Milky Way, but orbits around the center of the galaxy. It thus moves at the speed of 828,000 km per hour, in one of the four spiral arms of the galaxy: the Arm of Orion. It takes 230 million years for the solar system to go around the galactic center in this orbit.
How many missions have left the solar system?
Few missions have traveled far enough to leave the solar system. Two spacecraft launched by NASA in 1977 succeeded in doing so: Voyager 1 then Voyager 2. These probes reached interstellar space in 2012 and 2018 respectively. But their journey to leave the Oort cloud is not over — they remains several thousand years.
If you liked this article, you will like the following ones: do not miss them by subscribing to Numerama on Google News.