Welcome to the Solar System!

So where in the galaxy are we?
Figuring out where we are in our galaxy and even what our galaxy looks like is sort of like a cell inside our stomach trying to figure out where in the body it is located and what the body looks like on the outside. It’s NOT an easy task ! Astronomers have gathered data and determined that we are part of a spiral galaxy, the Milky Way, which is around 100,000 light years across. Astronomers also think that we are out on one of the spiral arms rather than near the center (good thing, too, because they believe there may be a super massive black hole at the center!).

What objects are in our solar system?
Mercury is the smallest and the inner most planet in our solar system. This speedy little planet orbits the sun once every 88 days giving it the shortest year of all planets in the solar system. Mercury can be viewed from earth but only in the morning and the evening. It looks a lot like the moon because it is heavily cratered and has no natural satellites. One thing that is different, though, is that Mercury has an iron core. This iron core generates a magnetic field about 1% as strong as the Earths. It has extreme temperature differences between night and day - like 600 degrees Celsius!

Venus, the hottest planet, orbits the sun every 225 Earth days and rotates once on it’s axis once every 243 days, making it’s day longer than it’s year! Venus is named after Venus the Roman goddess of love since it is the brightest object in the night sky other than the moon. It is sometimes called the morning or evening star. Because it is a terrestrial planet and is close to the same size as Earth, it is sometimes called Earths sister planet. It’s surface is quite different that Earth’s, though. It is a constant 462 degrees Celsius, cloudy, and has sulfuric acid rain!

Earth, the third planet from the sun, is the largest of the terrestrial planets. It takes 365.26 days to revolve and 24 hours to rotate on it’s axis (which is tilted at 23.5 degrees). It is home to millions of species and you! Earth is the only planet known to support life, have liquid water on it’s surface, free oxygen in the atmosphere, and an ozone layer.
Mars is the fourth planet from the sun. The planet is named after the Roman god of war. It is called the red planet because of the red color on it's surface which is caused by iron oxide (rust). Mars is a terrestrial planet with a thin carbon dioxide atmosphere. It is the site of the highest known mountain, Olympus Mons, and the biggest canyon, Valley Marinaris, in the solar system.

The Asteroid Belt: In addition to 8 planets and three dwarf planets, our solar system is home to millions of smaller rocks known as asteroids. Many of these massive rocks orbit the sun in a belt known as the asteroid belt between Mars and Jupiter. The largest of asteroids in this region, Ceres, the largest known in this region, was upgraded from asteroid to dwarf planet after the discovery of a world, Eris, larger than Pluto and nearly twice as far away!

Jupiter, the king of all planets, is the fifth planet from the sun and the largest planet in the solar system. It is larger than all the planets in solar system combined. Jupiter is classified as a gas planet like Saturn, Uranus, and Neptune. Jupiter has four huge moons that are visible from Earth with binoculars or a small telescope and could each be in the ‘solar system hall of fame’. The largest moon in the solar system is Ganymede. Callisto is known for it’s craters while Io is famous for it’s volcanoes. Europa has a smooth, icy surface and may have liquid water beneath a thick layer of ice.

Saturn is the sixth planet from the sun and is famous for it’s beautiful rings. The other gas giants have rings, too, but not nearly as attractive. It is the second biggest planet in the solar system. This planet is named after the Roman god Saturnas. One of Saturn’s moons, Titan, is the only moon known to have a well developed atmosphere.

Uranus, named after the greek deity of the sky, is the seventh planet from the sun and is the third largest. It’s most notable characteristic is that it orbits the sun on it’s side with a 98 degree tilt. It’s blue-green disk is visible to the naked eye but ancient astronomers could not see it because it slow orbit and its dimness. Sir William Herschel announced its discovery March 13, 1781.
Neptune is the eighth (and farthest) planet from the sun and is a beautiful blue color. It is known for having two storms called the “great dark spot” and the “little dark spot”. It is named after Neptune, the Roman god of the sea and its symbol is Neptune's trident. It was discovered September 23, 1846 and was the first planet discovered by mathematical prediction.

Dwarf Planets: Planets, according to the most recent definition, must meet three requirements. They must 1) be a celestial body orbiting the sun that is 2) massive enough to be rounded by it’s own gravity and have 3) cleared it’s orbital region of debris. Three large objects in our solar system meet the first two of these requirements but not the third so they are called dwarf planets. They are Ceres, Pluto, and Eris. The term dwarf planet was adopted in 2006.

Asteroids & Their Kin: Asteroids are sometimes called small planets or minor planets. They are large rocks (bigger than meteoroids but smaller than planets) that orbit the sun. Meteoroids, on the other hand, are small rocks in space that orbit the sun. When one of them enters the Earth’s atmosphere it heats up because of friction and gives off light - this is called a meteor. If the meteoroid survives the trip through our atmosphere and strikes the Earth, it is called a meteorite. The final solar system object we will discuss here is a comet. Comets are like dirty snow balls following crazy orbits around the sun. As they approach the sun the solar wind evaporates the ice and blows particles off the surface of the comet creating a tail. Interestingly, because of the solar wind the tail always points away from the sun.

How did the solar system get here?
One explanation for the formation of the solar system is called the Nebular Hypothesis. First suggested in the 1700s by Pierre Laplace, this idea has been modified slightly since that time and is still the most common hypothesis. It suggests that our solar system began as a nebula (a huge cloud of gas and dust in space) that began to spin and collapse due to gravity. As the nebula spun faster and faster, a protostar began to form in the center. A disk of gas and dust surrounded the protostar and this disk was warmer at the center than at the edges. Clumps of matter began to form slowly as particles of gas and dust collided and stuck together (called accretion). These clumps, called planetesimals, that formed closest the center contained rocky elements. The lighter elements were blown away from the center and began to accumulate in the outer planetesimals. Collisions of particles and, occasionally, planetesimals, resulted in the planets, asteroids, and other solar system bodies we see today.
As with other hypotheses, the Nebular Hypothesis has difficulty accounting for some of the data that have been collected but is one attempt to use what we see today to explain what may have happened in the past. Perhaps you will be one who gathers data that refines this hypothesis, supports a totally different hypothesis, or leads you develop a whole new explanation for the creation of the solar system!

Solar system data at a glance:


Special Thanks to Clayton Webster for his work at gathering information for and writing most of the text section on the planets.

http://galaxyknight.com/galaxyknight/solar_system.htm (for solar system picture)
Maran, Stephen P. Astronomy for Dummies. Wiley Publishing. 2005
Mosley, John. Starry Night Companion. Imaginovia Corp. 2004
Patterson, Roger. Evolution Exposed. Answers In Genesis. 2008
Exploring Earth Science. Prentice Hall. 1997