Hua Feng: They all know that Saturn and Jupiter are very far away.

Jupiter's farthest distance from the Sun is 816,520,800 kilometers, or about 816.5 million kilometers, or 5.46 AU. The closest distance is 740,573,600 km, or about 740.6 million km, or 4.95 AU.

Saturn's maximum distance from the Sun is 1,513,325,783 km, or about 1,513.3 million km, or 10.116 AU. The closest distance is 1,353,572,956 km, or about 1,353.6 million km, or 9.05 AU.

Then, when Saturn and Jupiter are on the same side of the Sun, Saturn is at perihelion and Jupiter is at aphelion, Saturn is closest to Jupiter, with a distance of 807.6 million kilometers, or 3.59 AU. That is, the distance between Saturn and Jupiter at this time is 3.59 times the distance from the Earth to the Sun.

When Saturn and Jupiter are on opposite sides of the Sun, and both Saturn and Jupiter are at aphelion, Saturn is furthest from Jupiter, at a distance of 2,329.8 million kilometers, or 15.576 AU. That is, the distance between Saturn and Jupiter at this time is 15.576 times the distance from the Earth to the Sun.

Although it took a long time to travel, they were not idle on the road, and they were arranged to reacquaint themselves with the solar system.

The Sun is the parent star of the solar system, and it is also the only celestial body in the solar system that emits its own light, and it is also the main and important member. It has enough mass (about 330,000 times that of the Earth) to suppress and withstand the enormous energy generated by nuclear fusion, and to allow the energy to flow steadily into space in the form of radiation, such as visible light.

The Sun is classified as a medium-sized yellow dwarf, but it's easy to get mistaken for a name, but in fact, the Sun is quite large and bright in our galaxy. Stars are classified according to the surface temperature and brightness of the Herrault chart. In general, hotter stars are brighter, and the stars that follow this pattern are located in the so-called main-sequence zone, where the Sun is in the center. However, there are not many stars that are larger and brighter than the Sun, and there are many stars that are fainter and colder.

The Sun is in the prime of its stellar evolution and has not yet exhausted the hydrogen needed for fusion at its core. The sun is still getting brighter day by day, and in the early days it was only 75% brighter than it is today.

Calculating the ratio of hydrogen to helium in the Sun's interior, it is believed that the Sun has completed half of its life cycle, and after about 5 billion years it has exhausted the hydrogen for nuclear fusion, and the Sun will leave the main-sequence stage and become a larger and brighter red giant, but with a lower surface temperature, thousands of times brighter than the Sun was in middle age.

The Sun is the star of the first family of stars, which was born in the late evolution of the universe, and it has more metals heavier than hydrogen and helium than the stars of the second group (this is an astronomical saying: everything with an atomic number greater than helium is a metal). ）。 Elements heavier than hydrogen and helium are formed in the core of stars and must be released into the universe by a supernova explosion.

In other words, these heavy elements were only present in the universe after the death of the first generation of stars. The oldest stars have only a small amount of metal, and the later ones have more metal. The high metal content is believed to be the key to the development of solar energy in the satellite system, as planets are formed from accumulated metallic materials.

In addition to light, the sun also emits a constant stream of electrons (plasma), also known as the solar wind. This stream of fine particles, which travels at a speed of 1.5 million kilometers per hour, creates a thin atmosphere (heliosphere) in the solar system that reaches at least 100 astronomical units (heliopause), which is known as interplanetary matter. The sunspot cycle (11 years) and frequent flashes and coronal mass ejections cause disturbances in the heliosphere, resulting in a space climate. The heliospheric sheet of current produced in the interplanetary matter by the magnetic field that rotates with the rotation of the sun is the largest structure in the solar system.

The Earth's magnetic field protects the Earth's atmosphere from its interaction with the solar wind. Mercury and Venus, on the other hand, have no magnetic fields, and the solar wind causes their atmospheres to gradually disappear into space. Auroras produced by the interaction of the solar wind and the Earth's magnetic field can be seen near the Earth's magnetic poles, such as the South and North Poles.

Cosmic rays come from outside the solar system, the heliosphere is a barrier to the solar system, and the planet's magnetic field also provides some protection for the planet itself. The density of cosmic rays in interstellar matter is related to the intensity of the solar magnetic field cycle, so it is still unknown how much cosmic rays change in the solar system.

Interplanetary matter is accumulating into cosmic dust in at least two disk-shaped regions. The first region is the ecliptic dust cloud, which is located in the inner solar system and is the cause of zodiacal light. They may be created by the collision of celestial bodies and planets within the asteroid belt. The second region extends in the range of about 10~40 AU, which may have been created by objects in the Kuiper Belt under similar mutual impacts.

The inner solar system is traditionally the name given to terrestrial planets and asteroid belt regions, which are mostly made up of silicates and metals. This region is squeezed close to the Sun, with a radius shorter than the distance between Jupiter and Saturn.

Inner Planets The four inner planets, or terrestrial planets, are characterized by high density, made of rocks, few or no moons, and no ring systems.

They are composed of minerals with high melting points, such as silicate minerals, a crust and a semi-liquid mantle that make up the surface solids, and a metal core composed of iron and nickel. Three of the four (Venus, Earth, and Mars) have substantial atmospheres, and all have impact craters and surface features of geological formations (grabens, volcanoes, etc.). Inner planets are easily confused with inner planets (Mercury and Venus) that are closer to the Sun than Earth. The planets orbit in a plane and in one direction.

Mercury (Me

cu

y) ( ☿ ) (0.4 AU) is the closest planet to the Sun and the smallest planet (0.055 Earth mass). It has no natural satellites, and the only known geological features are the craters, presumably folded ridges created during early history and contraction.

Mercury, including gas atoms blasted out by the solar wind, has only an insignificant atmosphere. As of 2013, it is not yet possible to explain the relatively large iron core and thin mantle. Hypotheses include the fact that the huge shock stripped away its shell, and that the solar energy of its youth inhibited the growth of the shell.

Venus (Ve

US) ( ♀ ) (0.7 AU) is similar in size to Earth (0.86 Earth mass) and has a thick silicate mantle surrounding the core, as well as evidence of a thick atmosphere and internal geological activity. However, its atmosphere is 90 times denser than the Earth's, very dry, and has no natural satellites.

It is a scorching planet with a surface temperature of over 400°C, most likely caused by the abundance of greenhouse gases in the atmosphere. There is no clear evidence that the geological activity of Venus is still ongoing, but the atmosphere without the protection of the magnetic field should be depleted, so it is believed that the atmosphere of Venus was replenished by volcanic eruptions.

Earth (Ea

th) (⊕ (1 AU) is the largest and densest of the inner planets, and the only planet with ongoing geological activity and life (scientists have not yet discovered other creatures from space). It also has a hydrosphere and observed plate structure that is unique among terrestrial planets. Earth's atmosphere is also completely different from other planets, and has been modified by the living organisms here to contain 21% free oxygen.

It has only one moon, the Moon, which is also the only large moon among terrestrial planets. The Earth's revolution (the Sun) takes about 365 days, and its rotation takes about 1 day. (The Sun doesn't always shine directly at the equator because the Earth tilts slightly as it revolves around the Sun.) ）

Mars (Ma

s) ( ♂ ) (1.5 AU) is smaller than Earth and Venus (0.17 Earth mass), has only a rarefied atmosphere dominated by carbon dioxide, and its surface, such as Mount Olympus, has dense and massive volcanoes, and Mariner Canyon has deep grabens, indicating that there was still intense geological activity not so long ago. Mars has two natural small moons, Demos and Vobers, which may have been captured asteroids.

Asteroids are the most important members of the solar system's small bodies, consisting mainly of rocks and non-volatile matter.

The main asteroid belts are located between the orbits of Mars and Jupiter, 2.3 to 3.3 AU from the Sun, and they are thought to be remnants of material that failed to aggregate due to Jupiter's gravitational disturbances during the formation of the solar system.

Asteroids range in size from hundreds of kilometers to microns. With the exception of Ceres, the largest asteroid, all asteroids are classified as small bodies of the solar system, but several asteroids, such as Vesta and Physis, may be reclassified as dwarf planets if they can be confirmed to have reached hydrostatic equilibrium.

The asteroid belt is home to tens of thousands, possibly millions, of small objects with diameters of more than a kilometer. Still, the total mass of the asteroid belt is unlikely to reach one thousandth of the mass of the Earth. The members of the asteroid's main belt are still sparsely populated, so no spacecraft have had an accident while crossing it.

Small objects with a diameter of 10 to 10.4 meters are called meteoroids.

Ceres

ES) (2.77 AU) is the largest object in the main belt and the only dwarf planet in the main belt. Its diameter is close to 1,000 kilometers, so its gravitational pull is strong enough to make it a sphere.

When it was discovered in the early 19th century, it was considered a planet, but it was reclassified as an asteroid in the 1850s as more small bodies were discovered, and again as a dwarf planet in 2006.

Asteroids in the main belt can be divided into several asteroid groups and asteroid groups based on orbital elements. Asteroid moons are small bodies orbiting larger asteroids, and their identification is not as clear as that of satellites orbiting planets, because some moons are almost as large as the orbiting parent body.

The Trojan asteroid is located at Jupiter's L4 or L5 point (the unstable gravitational equilibrium point in front of and behind the planet's orbit), but the name "Troy" is also used for small objects located at the Lagrange point in the orbit of other planets or moons. The Hilda are a group of asteroids whose orbital period resonates with Jupiter 2:3, and when Jupiter makes two revolutions around the Sun, the group of asteroids makes three revolutions around the Sun.

The inner solar system also contains many "naughty" asteroids and dust particles, many of which pass through the orbits of the inner planets.

The central region of the solar system is home to gas giants and their planet-sized moons, as well as many short-period comets, including centaur herds. This area has no traditional name and is occasionally grouped under the "outer solar system", although the outer solar system usually refers to the region beyond Neptune. The main components of solids in this region are "ice" (water, ammonia, and methane), unlike the rocky inner solar system.