The Solar System

The solar system is an assemblage of eight (formerly nine) planets, many planetary satellites or moons, asteroids, and comets. It also contains a vast reaches of highly tenuous gas and dust known as the interplanetary medium.

The Sun shoots out a stream of particles called the solar wind. This flows outward through the solar system and into interstellar space.

The Sun

The Sun is the center of our solar system. It’s also the source of all light and heat we see here on Earth. It’s one of a hundred billion stars in our galaxy, and it orbits 25,000 light-years from the galactic core.

The Sun was formed 4.6 billion years ago, when part of a molecular cloud exploded into space. As the sun grew larger and more massive, it became so hot that the gases in its core fused together to form hydrogen. This process released enormous amounts of energy in the form of light and heat.

Currently, the sun is a G-type main-sequence star (G2V), but in about 5 billion years it will turn into a red giant. At this point, the Sun will consume everything in its path, including planets like ours!

Our Sun’s atmosphere, or ‘photosphere,’ is made up of two gases: hydrogen and helium. Around 99% of the Sun’s energy comes from hydrogen fusing into helium. The other 1% is made up of oxygen, nitrogen and other gases and chemicals.

Most of the energy from the sun is transmitted by radiation. The Sun’s temperature ranges from 6200 degrees Celsius at the surface to 3700 degrees Celsius inside its core.

There are three distinct layers within the Sun: a radiative zone, a convective zone and a core. The outer layer, the chromosphere, is relatively stable because of the effects of gravity and gas pressure. This layer is separated from the next layer, the corona, by a region called the solar transition region (STR).

The Asteroids

The Asteroids are rocky and metallic bodies that orbit around the Sun, in all different shapes and sizes. They are the remnant debris of the planet-formation process in our solar system.

Many asteroids are located in the asteroid belt between Mars and Jupiter. The asteroid belt is estimated to contain between 1.1 and 1.9 million asteroids larger than 1 kilometer (0.6 miles) in diameter, and millions of smaller objects.

Most asteroids are about a half mile to 60 miles wide. Smaller ones are called meteoroids and can come close to Earth.

Some asteroids are spherical, like Ceres and Vesta; others are rougher, more irregularly shaped, and are similar to the moons of our planets. Some are even very big, like Hygiea.

Asteroids are made of all kinds of materials, ranging from metal to rock to organic compounds. They can have a variety of other properties, such as temperature, brightness, and the length of time that they block out the star when they pass in front of it.

The most important information about asteroids comes from their orbits and how they change over time. Astronomers use these orbits to determine how the objects are formed, what they are made of, and whether they are hazardous to the planets.

Asteroids have an extremely long history of study, from Galileo’s observations in the early 1900s to the modern day, when spacecraft like NASA’s NEAR Shoemaker and Dawn studied asteroids. JAXA’s Hayabusa and Hayabusa2 also observed asteroids, and OSIRIS-REx plans to return samples of some asteroids to Earth.

Asteroids are a fascinating collection of planetary debris that scientists continue to study, both for their role in the formation of the solar system and for their potential hazards to Earth.

The Planets

Planets are rocky bodies that orbit around the Sun. They have a gravity that makes them spherical and clears the neighborhood of smaller objects around their orbits, which are called moons.

In the early years of the Solar System, many worlds formed in a swirling cloud of gas and dust. They collided and grew into protoplanets. During this time, the solar system was full of tiny asteroids that orbited in the asteroid belt.

These asteroids were molten rocks that eventually cooled to the point where they solidified and became rocky planets. The four inner rocky planets (Mercury, Venus, Earth and Mars) formed in this area about 4.568 billion years ago.

The four outer gas-giant planets (Jupiter, Saturn, Uranus and Neptune) were formed in the Oort Cloud some time later. They were too far away from the Sun for stellar winds to blow off their gases, so they remained large enough to have cores made of rock and metals.

Jupiter, for example, is 11 times the size of Earth and twice as big as all the other planets combined. Its atmosphere is a mixture of hydrogen and helium, but it also contains ammonia, water, methane, hydrogen sulfide and other trace gases that form colorful clouds in its frosty conditions.

Several of the planets’ moons orbit in a similar fashion to their parent bodies, but in different directions. Titan, for example, is larger than Mercury and shows the remnants of a primitive atmosphere that is denser than Earth’s.

Astronomers are hunting for extrasolar planets, or planets that orbit other stars beyond our solar system. One NASA mission, Kepler, is monitoring 100,000 stars a few hundred to a few thousand light-years away, looking for a world that could support life.

The Moon

The Moon orbits Earth in a slightly eccentric circular path around the planet, following Kepler’s laws of planetary motion. Its distance from Earth is about 384,000 km (238,000 miles) and its equatorial radius is 1,738 km (1,400 miles).

As it orbits Earth, the Moon reflects sunlight as it travels towards or away from us. As the Moon is closest to us, it appears larger and brighter than when it is further from Earth.

This effect is caused by the difference in speed between Earth and the Moon as it moves around each other in their elliptical orbits. When the Moon is at perigee, it can appear about 12% bigger and 30% brighter than when it is farthest from Earth (apogee).

Another factor affecting the Moon’s apparent size is its non-circular orbit. As it moves closer to Earth, its angular speed is faster than its rotation, which causes the Moon to look smaller in our eyes as it approaches its nearest point to Earth (perigee) and bigger as it gets further away (apogee).

However, the non-circular nature of the Moon’s orbit also means that it reflects less light at its closest approach to Earth and more light at its furthest point from Earth than at other points in its orbit. This enables it to appear as a supermoon, when the Moon is full and closest to Earth (perigee).

Because of its close proximity to Earth, the Moon has influenced the Earth’s rotation for a long time. This is caused by tidal friction between the two bodies, which slows Earth’s rotation and lengthens our day at a rate of about 1.4 milliseconds every century.

Other Space Bodies

The Solar System consists of eight planets and many other space bodies that orbit the Sun. It is located in the Milky Way galaxy, one of the largest galaxies in the universe.

The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These planets are formed out of a giant rotating cloud of gas and dust.

There are also thousands of objects in the solar system that are not planets or even stars. These include asteroids, comets, and small planetary satellites.

Most of these objects are in a region called the asteroid belt. This is a nearly flat ring of hundreds of thousands of rocky objects between Mars and Jupiter. These objects range in size from tiny dust particles to the dwarf planet Ceres.

Another important area of the Solar System is known as the Kuiper belt. This region is home to a large number of icy objects that resemble comets and moons from outer space.

This belt extends well beyond the planets in a region called the Oort Cloud. These icy objects are thought to be the birthplace of long-period comets, and they are considered a critical piece in the puzzle of the Solar System’s formation.

The ice on these objects vaporizes when they come closer to the Sun, producing a beautiful trail behind them. They are considered important targets for NASA’s spacecraft because they can teach us more about the early days of our solar system and about the origins of our own planetary systems.

The International Astronomical Union (IAU) has established a number of standards for naming astronomical objects, such as planets and moons. These conventions are meant to help astronomers understand their subjects and to improve the public’s understanding of astronomy.