In depth | Our Solar System – NASA Solar System Exploration

introduction

The planetary system we call home is located in an outer spiral arm of the Milky Way galaxy.

Our solar system consists of our star, the Sun, and everything gravity-bound to it – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets and meteoroids.

Beyond our own solar system, there are more planets than stars in the night sky. So far we have discovered thousands of planetary systems orbiting other stars in the Milky Way, with more planets discovered. Most of the hundreds of billions of stars in our galaxy are thought to have their own planets, and the Milky Way is just one of the 100 billion galaxies in the universe.

While our planet is in some ways just a dot in the vast cosmos, we have plenty of company there. It seems that we live in a universe full of planets – a network of countless stars accompanied by families of objects, perhaps some with life of their own.

Namesake

Namesake

There are many planetary systems like ours in the universe, with planets orbiting a host star. Our planetary system is called the “Solar System” because our Sun is called Sol, after the Latin word for Sun, “solis,” and everything related to the Sun that we call “solar.”

Size and distance

Size and distance

Our solar system extends far beyond the eight planets that orbit the Sun. The solar system also includes the Kuiper belt located beyond the orbit of Neptune. It’s a sparsely-busy ring of icy bodies, nearly all of which are smaller than the most popular Kuiper Belt object – the dwarf planet Pluto.

NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. Credit: NASA/JHUAPL/SwRI | Full caption and image

Beyond the fringes of the Kuiper Belt lies the Oort Cloud. This giant spherical shell surrounds our solar system. It has never been observed directly, but its existence is predicted based on mathematical models and observations of comets that likely originated there.

The Oort Cloud is made up of icy space debris – some larger than mountains – orbiting our Sun up to 1.6 light-years away. This shell of material is thick, ranging from 5,000 astronomical units to 100,000 astronomical units. An astronomical unit (or AU) is the distance from the Sun to the Earth, or approximately 93 million miles (150 million kilometers). The Oort Cloud is the boundary of the Sun’s gravitational influence, where orbiting objects can turn around and return closer to our Sun.

The Sun’s heliosphere does not extend that far. The heliosphere is the bubble created by the solar wind – a stream of electrically charged gas blowing from the Sun in all directions. The limit where the solar wind is suddenly slowed down by the pressure of interstellar gases is called the terminal shock. This edge occurs between 80 and 100 astronomical units.

Two NASA spacecraft launched in 1977 went through the final blow: Voyager 1 in 2004 and Voyager 2 in 2007. Voyager 1 went interstellar in 2012 and Voyager 2 joined in 2018. But it will be several thousand years before the two Voyagers leave the Oort cloud.

Moons

Moons

There are over 200 known moons in our solar system and several more awaiting discovery confirmation. Of the eight planets, Mercury and Venus are the only ones without a moon. The giant planets Jupiter and Saturn lead the number of moons in our solar system. In some ways, the swarms of moons around these worlds look like mini-versions of our solar system. Pluto, smaller than our own moon, has five moons in its orbit, including Charon, a moon so large it makes Pluto wobble. Even tiny asteroids can have moons. In 2017, scientists discovered asteroid 3122 Florence had two tiny moons.

Solar System Family Portrait

These six narrow-angle color images were taken from the very first “portrait” of the solar system taken by Voyager 1, which was more than 4 billion kilometers from Earth and about 32 degrees above the Earth. ecliptic. Credit: NASA Planetary Photojournal

Training

Training

Our solar system formed about 4.5 billion years ago from a dense cloud of interstellar gas and dust. The cloud collapsed, possibly due to the shock wave from a nearby explosive star, called a supernova. When this cloud of dust collapsed, it formed a solar nebula – a spinning, swirling disc of matter.

At the center, gravity pulled in more and more matter. Eventually, the pressure in the nucleus was so strong that the hydrogen atoms began to combine and form helium, releasing an enormous amount of energy. With this, our Sun was born, and it eventually amassed over 99% of the available matter.

Material further into the disc was also clumping together. These clusters crashed into each other, forming larger and larger objects. Some of them grew large enough that their gravity shaped them into spheres, becoming planets, dwarf planets and large moons. In other cases, the planets did not form: the asteroid belt is made up of pieces of the early solar system that could never quite fit together into a planet. Other small remnants became asteroids, comets, meteoroids and small irregular moons.

Structure

Structure

The order and arrangement of the planets and other bodies in our solar system is due to the way the solar system was formed. Closer to the Sun, only rocky material could withstand the heat when the solar system was young. For this reason, the first four planets – Mercury, Venus, Earth and Mars – are terrestrial planets. They are all small with solid, rocky surfaces.

Meanwhile, the materials we used to see as ice, liquid, or gas settled in the outer regions of the young solar system. Gravity has brought these materials together, and this is where we find the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune.

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