Origin of the Solar System – Flashcards

from debris that flew into space after a star nearly collided with our Sun. As the star passed close to the Sun, hot gas was stripped from both the Sun and the star, and got lumped together to form the planets. Material from the Sun formed the four planets closest to the Sun; and material from the passing star formed the planets farther away from the Sun.

all the planets move around the Sun in the same direction, since the encounter would have sent material out in the same direction. But it has two main problems. The first is that hot gas expands; it does not contract. So the gas that was flung from the star and the Sun would not have lumped and concentrated into planets. Second, encounters between stars are extremely rare. The chance of a star nearly colliding with our own Sun is just not likely

Scientists almost universally believe that the solar system began as a large, shapeless cloud of dust and gas, called a nebula. About five billion years ago, something disrupted the nebula—perhaps a supernova explosion from a nearby star. The explosion forced all of the material in the nebula to concentrate together.

Just like an ice skater spins faster when she brings her arms in close to her body, the nebula began to spin faster and faster because all of its mass was now concentrated in one central region. The nebular cloud began to collapse under the force of its own gravity. This process probably took about 100,000 years. During that time, most of its mass became more and more concentrated toward the center. The center also became progressively hotter and hotter.

Eventually, the spinning motion flattened the nebular cloud into a disk shape, much in the same way that you can flatten a ball of pizza dough by spinning it around. All the nebula's individual dust particles began to stick together and form larger bodies, called planetesimals. The planetesimals were young objects that were not yet large enough to be called planets. But they continued to grow over millions of years, gradually getting bigger and bigger.

The planetesimals grew as dust collided with and stuck to them, through a process called accretion. Through accretion, tiny planetesimals grew to the planets that we know so well today—Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. It took millions of years for the tiny planetesimals to develop into fully formed planets. Once they were formed, there was a complete solar system. The Sun developed in the hot massive center and the planets began their orbits around it. They are bound to the Sun by gravity and they stay in their orbits around it because of gravity. Ninety-nine percent of the mass of our solar system is concentrated in the Sun, which is the center of the solar system. The nebular hypothesis replaced the close encounter hypothesis and is now widely accepted as the better model of how our solar system formed.

The composition of the planets also supports the nebular hypothesis. Once the Sun formed in the center, solar wind swept away light gases, like hydrogen and helium, from areas close to the Sun. Farther out in the solar system, the solar wind would have been much weaker and not as effective in driving away these gases. This is demonstrated by fact that planets that are farthest from the Sun are made mostly of swirling balls of hydrogen and helium gas. However, the planets close to the Sun have rocky compositions. Their primordial hydrogen and helium gases were likely swept away. Look up into the night sky and find the constellation, Orion. Just south of Orion's belt is the Orion Nebula. Advanced telescope images of the Orion Nebula show approximately 700 stars in various stages of formation. Within the Orion Nebula, we can see several disks, which are believed to be the beginnings of solar systems. In this picture, you can see several of these regions within the Orion Nebula.

Selection 1: set off hydrogen fusion in the sun Selection 2: forced nebular material to concentrate in a central region and begin spinning Selection 3: allowed an area of the universe to become cool enough for matter to accumulate Advisor 1: The solar system began as a cloud of dust and gas called a nebula. That material had to be shaped and concentrated somehow. Advisor 2: A supernova explosion would have sent shockwaves throughout space. It would have disrupted any nearby nebula. Advisor 3: The energy from a supernova explosion might have been just what was needed to make individual dust particles accumulate together to form planets. Advisor 4: After the supernova explosion particles of dust in nearby nebula would have started colliding with and sticking to each other. Advisor 5: You needed some kind of activity that could make individual dust particles collide together and become concentrated

Selection 1: by dust particles colliding and sticking to each other Selection 2: by nuclear reactions in the center of the nebular cloud Selection 3: by material breaking off of the sun during collapse of the nebular cloud Advisor 1: The planetesimals started out small and grew larger over millions of years. Advisor 2: They were small bodies that were not yet large enough to be planets. Gravity played a large role in how they came together. Advisor 3: Planetesimals were made through the process of accretion, as small bodies were joined together and grew larger and larger over time. Advisor 4: Remember that these small planets-to-be grew slowly as more and more matter was added to them. Advisor 5: Planetesimals grew particle by particle through the process of accretion

Selection 1: It became colder and lighter. Selection 2: It became massive and hot. Today it's our sun. Selection 3: It became dispersed as tiny particles were ejected from it. Advisor 1: Think about what the center of the solar system is today. Advisor 2: Nearly 99 percent of the mass of our solar system today is in the center. Advisor 3: As mass accumulated in the center, the early solar system began spinning rapidly. Advisor 4: I think you should remember that the center of the solar system is where nearly all of its mass is now found. Advisor 5: What's the center of our solar system today? That's your big clue.

Our solar system is located in one of the spiral arms of the Milky Way Galaxy. Specifically, we are in an arm of the Milky Way called the Orion Arm. You can see our Sun near the Orion spur in this diagram. (The term spur means an arm of a galaxy that is relatively smaller than the others.) Our solar system is a very tiny part of the Milky Way Galaxy, and our Sun is only one of billions of stars in the galaxy. The next closest star system to our solar system is the Alpha Centauri system, also in the Milky Way. Though not yet proven, Alpha Centauri may also have planets orbiting a central sun.

Our solar system orbits the center of the galaxy, just like planets orbit the Sun, or the center of the solar system. It takes about 250 million Earth years for the Sun to make one complete revolution of the galaxy center. This span of time is called a galactic year. Right now, the solar system is moving through a cloud of dust and gas within the Milky Way, known as the Local Interstellar Cloud. In this diagram, the yellow dot is our solar system. The Orion Arm, the part of the Milky Way in which we are located, is called the Local Spur on this diagram

When the solar system formed, two distinct zones developed. Close to the Sun, rock and metal materials dominated. The planets that formed from accretion of these materials became the four planets closest to the Sun—Mercury, Venus, Earth, and Mars. They are called the inner planets, because they are found in the inner solar system, close to the Sun. They are also called the rocky or terrestrial planets. The word terrestrial means "earth-like." Though they are certainly not entirely like Earth, they have many features in common with Earth, such as silicate rocks and central metallic cores. They have solid surfaces, current or past tectonic activity, and atmospheres derived from volcanic activity, as well as from living things in the case of Earth.

Just beyond the inner planets is a belt of asteroids called, simply, the asteroid belt. Asteroids are small objects that orbit the Sun and are not large enough to be planets. Most scientists believe the asteroids are left over material that never came together to make a planet because of gravitational influences from Jupiter

Mercury, Asteroid Belt, Earth, Rocky Planets, Venus, Mars

Jupiter, Uranus, Saturn, Pluto, Neptune, Planets made of Gas and Ice

Part of the galaxy in which our solar system resides

Our home galaxy

Small body that orbits the Sun

Star system closest to our own solar system

Process by which planets grow during solar system formation

A planet made of silicate rocks and a metallic core

Time it takes the Sun to make one revolution around the galaxy

Kepler's first law of planetary motion says that planets orbit the Sun in ellipses, not perfect circles. Some planets have orbits that are more elliptical than others. The more "flattened" a planet's orbit is, the more elliptical it is. A planet's degree of orbital flattening is called its eccentricity. With the exception of Pluto and Mercury, most of the planets display very little eccentricity.

Kepler's second law deals with the speed of planets in their orbits. It states that planets change speed relative to their position. They speed up when they are close to the Sun and slow down when they are farther away from the Sun. This means that over equal periods of time, a planet will move equal distance. When close to the Sun, a planet may go a longer distance because it is moving fast; when far away from the Sun a planet slows down and goes a shorter distance. In other words, the speed balances out the distance, so a planet always moves the same distance in the same amount of time, regardless of how close it is to the Sun.

Kepler's third law compares a planet's movements to the movements of other planets. It is more mathematical in nature than the first two laws, but essentially, it says that the orbiting time of a planet is a function of the size of the orbit. The larger the orbit, the longer the orbit time.

Kepler's first law of planetary motion says that planets orbit the Sun in ellipses, not perfect circles. Kepler's second law deals with the speed of planets in their orbits. It states that planets change speed relative to their position. They speed up when they are close to the Sun and slow down when they are farther away from the Sun. This means that over equal periods of time, a planet will move equal distance. The third law compares a planet's movements to the movements of other planets. It is more mathematical in nature than the first two laws, but essentially, it says that the orbiting time of a planet is a function of the size of the orbit. The larger the orbit, the longer the orbit time.

-Every object in the universe is attracted by gravity to every other object in the universe. -The strength of attraction between any two objects is proportional to their masses and the distance between them. -More massive objects exert greater gravitational force, but large distances between objects diminish the force of gravity.

The strength of the gravitational force increases with the mass of the object

The strength of the gravitational force decreases with the distance between objects. The greater the distance, the smaller the gravitational force exerted on other objects.

Differences in mass and distance keep every object from flying toward every other object