The Solar System

Planets in Our Solar System

What is the solar system A system of nine planets and all other celestial bodies that orbit the sun. Our solar system also contains all of the meteoroids, asteroids, and comets that are in orbit around the Sun and all of the moons that orbit around the eight planets. The eight planets in our solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The sun contains 99.86% of the mass of the solar system.

How the solar system formed A nearby star might have exploded, and the shock waves from this event could have caused the cloud to start contracting (4.6 billion yrs ago). The cloud’s density became greater & attraction of gravity pulled more gas and dust toward the cloud center. This caused the cloud to rotate faster, which in turn flatten into a disk with a dense center. The temperature of the cloud increased to 10 million degrees celsius and nuclear fusion began. The sun was created.

Planet Formation Not all of the nearby gas, ice and dust was drawn into the core of the cloud. The matter that did not get pulled into the cloud’s center collided and stuck together to form the planets and asteroids.

Mercury Closest to the sun Second-smallest planet No atmosphere Extreme temperatures of -170 C – 430C Has no moons

Venus Called the Earth’s sister planet Thick atmosphere made mostly of carbon dioxide Droplets of sulfuric acid in atmosphere give clouds a yellowish color Temperatures of 450C to 475c

Earth Atmosphere protects life Surface temperatures allow water to exist as solid, liquid and gas Only planet where life is known to exist Has one large moon

Mars Surface appears reddish-yellow because of iron oxide in rocks Ice caps are made of frozen carbon dioxide and water Surface temperature range from -125 C to 35 C Channels indicate that water has flowed on the surface

Jupiter Largest planet Has faint rings Atmosphere is mostly hydrogen and helium; continuous storms swirl on the planet-the largest is the Great Red Spot Has 4 large moons & 24 smaller moons

Saturn Second-largest planet Thick atmosphere is mostly hydrogen and helium Has complex ring system Has at least 30 moons Titan (moon) is larger than mercury

Uranus Large gaseous planet with thin, dark rings Atmosphere is hydrogen, helium and methane Axis of rotation is parallel to plane of orbit

Neptune Is sometimes farther from the sun than pluto Methane in atmosphere causes it bluish-green color Has dark-colored storms in atmosphere Has 8 moons

Pluto Small, icy-rock planet with thin atmosphere Single moon, Charon, is half the diameter of the planet Farthest from the sun

Milky Way Our solar system is located in the Milky Way Galaxy. The Milky Way Galaxy is a spiral galaxy that contains hundreds of billions of stars. In fact, in areas on Earth without excessive light pollution, the stars of the Milky Way create a band of light that can be seen in the night sky. The entire Milky Way Galaxy is about 100,000 light years across.

Nebulae A nebula (plural = nebulae) is a cloud of dust and gas that exists in space, usually between stars. Nebulae can generally be classified into two categories based on their size and shape—planetary nebulae and diffuse nebulae.

Planetary Nebulae A planetary nebula is a relatively small, ball-shaped nebula that surrounds a star. The nebula forms from material ejected from the star's outer layers as the star begins to collapse. The Hubble Space Telescope image below shows a planetary nebula.

Diffused Nebulae A diffuse nebula is a larger nebula with an irregular shape. Diffuse nebulae located near stars reflect starlight or give off their own bright light. The image below shows a diffuse nebula.

Galaxies Stars do not exist as separate entities in space, but instead belong to large groups of other stars that are held together by the force of gravity. These large groups of stars are called galaxies. Scientists believe that there are billions of galaxies in the Universe, and that most galaxies contain billions of stars. 4 types of galaxies: Spiral Barred spiral Elliptical Irregular

Spiral Galaxy these galaxies are relatively flat and have a bulge in the middle. These galaxies have arms that spiral out from the center. Our Milky Way galaxy is a spiral galaxy, and the Sun, our closest star, is one of the stars in it. Below is a picture of the spiral galaxy M81.

Barred Spiral Galaxy these galaxies are shaped like spiral galaxies, except for the fact that the arms begin spiraling out from a straight line of stars instead of from the center. Below is a picture of the barred spiral galaxy NGC 1672.

Elliptical Galaxy these galaxies look like a round or flattened ball and contain little gas and dust between the stars. These are often described as taking on the shape of a football. Below is a picture of the elliptical galaxy NGC 1132.

Irregular Galaxy these galaxies have no discernible shape or structure. Below is a picture of the irregular galaxy I Zwicky 18.

Stars Stars are enormous spheres of plasma formed from strong gravitational forces. Plasma is the most energetic state of matter and is responsible for the characteristic glow emmitted by these heavenly giants. Hydrogen is the most abundant element found in stars. Over time, the hydrogen atoms are converted into helium through a process known as nuclear fusion.

Comets Comets are composed of dust and rock particles mixed with frozen water, methane and ammonia. Jan Oort, proposed a large collection of comets lie in a cloud outside the orbit of Pluto.

Asteroids Most of the asteroids lie between the orbits of Mars and Jupiter, but some have very elliptical orbits which bring them very close to Earth. They range in size from about 30% the diameter of our moon to pebble sized objects. In number, there are probably billion of asteroids in the solar system.      The largest known asteroid is Ceres which was the first asteroid to be discovered in 1801. Ceres is about 1/3 the size of our moon. It can be seen in amateur telescopes if one knows where and when to look.      The Galileo spacecraft passed through the asteroid belt twice on its way to Jupiter. The spacecraft passed only 16.000 km from the asteroid Gaspra in 1990 and returned excellent images. Gaspra is an oblong world measuring 20 by 12 by 11 km. It is covered by a layer of shattered soil about a meter deep. There are also numerous craters on Gaspra's surface.