Ch. 8 Astronomy: Solar System

Where is the Oort cloud?

Far beyond Neptune Approximately 100, 000 AU from the Sun

What is a solar nebula?

swirling disk of gas and dust that remained after the interstellar cloud contracted by its own gravity

In what direction do all the planets travel?

Counterclockwise

In what direction does the Sun spin?

Counterclockwise

Most planets spin on their rotation axis in what direction?

Counterclockwise There are two exceptions!

The Sun is composed of mostly ____ & ____. (a) hydrogen (71%) & helium (27%) (b) hydrogen (27%) & helium (71%) (c) hydrogen (71%) & molten iron (27%)

(a) hydrogen (71%) & helium (27%) The Sun is mostly composed of hydrogen and helium. It also contains trace amounts of other elements in vaporized form - carbon, iron, uranium, etc. We know that these other elements are in vaporized form because of the spectrum of the light the Sun emits.

In order of increasing distance from the Sun, what are the inner planets? (a) Mars, Earth, Mercury, Venus (b) Mercury, Venus, Earth, Mars (c) Mercury, Venus, Earth

(b) Mercury, Venus, Earth, Mars These are considered the inner planets. They are all "small" rocky bodies with little to no atmosphere.

In order of increasing distance from the Sun, what are the outer planets? (a) Jupiter, Saturn, Neptune, Uranus (b) Saturn, Jupiter, Uranus, Neptune (c) Jupiter, Saturn, Uranus, Neptune

(c) Jupiter, Saturn, Uranus, Neptune These are considered the outer planets. They are larger than the inner planets. They are gaseous and liquid. They have deep hydrogen rich atmospheres.

Two main types of planetesimals

1. rocky-iron ones near the Sun 2. Icy-rocky-iron ones far from the Sun

What is a dwarf planet?

A dwarf planet is any object orbiting the Sun that is large enough to have gravitational force to create a spherical shape but has not cleared itself from other objects around itself that add up to its own approximate mass.

What is an asteroid?

A large rocky or metallic body. Some are large enough to pull itself into a spherical shape and are considered dwarf planets.

What is a limitation to transiting?

A limitation is that smaller planets, such as terrestrial planets, only block less than 0.01% of a star's light which is very challenging to detect.

What is the Kuiper belt?

A region beyond Neptune composed of mostly icy objects. This includes Pluto, Eris, and dozens of other dwarf planets.

What is the asteroid belt?

A region located between Mars and Jupiter containing most of the solar system's asteroids.

What is the Oort cloud?

A region located far beyond Neptune that contains most of the solar system's comets .

The Sun is...

A star - a ball of incandescent gases. Its light and heat are generated by nuclear reactions in its core. It is the largest body in our solar system.

What is an interstellar cloud?

An enormous rotating aggregate of gas and dust located between the stars of our Galaxy. Most likely stars formed from them and contain all of the raw materials that eventually formed our entire Solar System.

Terrestrial planets have densities similar to ______.

Earth

Where is the Kuiper belt?

Beyond Neptune Approximately 50 AU from the Sun

What is an example of a large asteroid considered a dwarf planet?

Ceres

What is a comet?

Comets are icy bodies located very far away from the Sun. As they approach the Sun, they forms great tails of ice, gas, and dust as it vaporizes.

Why do astronomers believe that the Oort cloud surrounds our solar system in a roughly spherical shape?

Comets come from all directions and have orbits in all directions which suggests that the Oort cloud surrounds the solar system in all directions.

What is a limitation to Gravitational Lensing?

Gravitational lensing allows minimal follow up observations. This method relies on rare change alignments (and they measure millions of stars at once waiting for a change). We cannot go back to observe the results after the position of the star and orbiting planet changes.

Jupiter and Saturn are primary composed of ____.

Hydrogen and Hydrogen gases

What is a limitation to the Doppler Method?

It works best for massive objects. Smaller objects and planets may not produce a large enough effect to be measurable.

Jovian planets have much _____ densities than terrestrial planets. (a) lower (b) higher

Jovian planets have much lower densities!

Explain why Jovian planets have "no true surface".

Jovian planets have no true surface because their atmospheres just thicken with depth and eventually compress into liquid. There is no distinct boundary between atmosphere and solid crust.

Which planets are the "gas giants"?

Jupiter and Saturn

List the Jovian planets. Why are they called this?

Jupiter, Saturn, Uranus, Neptune They are called Jovian planets for their resemblance to Jupiter.

What are planetesimals?

Large chunks of material (1 mm to several km in size) from which the planets were formed. The result of small object colliding into each other over time to form larger objects.

Uranus and Neptune are primarily composed of ____.

Liquid water and other melted icy materials

List the terrestrial planets. Why are they called this?

Mercury, Venus, Earth, Mars They are called terrestrial planets for their resemblance to Earth.

How did the asteroid belt possibly form?

Most likely formed by all the left over pieces that did not get added when Jupiter formed or were disrupted by Jupiter's gravitational field and would not allow these pieces to congregate into their own planet

Which planets are the "ice giants"?

Neptune and Uranus

What is an exoplanet?

Other planets orbiting stars that are not the Sun

Planetesimals far from the Sun formed from ___ and ___.

Planetesimals far from the Sun formed from ice and frozen gases. Some iron and silicate as well.

Planetesimals near the Sun formed from ____ and ____.

Planetesimals near the Sun formed from iron and silicate particles.

What is now an example of a dwarf planet?

Pluto and/or Eris, Ceres

Pluto has long failed to fit into any of the previous categories. Why is this?

Pluto has failed to fit as a terrestrial planet or a Jovian planet. This is because of its small size, composition of ice and rock, and odd orbit. Its orbit is tilted relative to the other planets and sometimes crosses Neptune's path.

What is condensation?

Simply: The changing of a gas to a liquid. Condensation occurs when gas cools and its molecules stick together to form liquids and solids. Condensation occurred in the solar nebula as it cooled after its collapse into a disk.

What is the Gravitational Lensing Method?

The Gravitational Lensing Method is detecting a planet by the slight bend of light from a background star caused by an orbiting planet's gravitational field. This bending magnifies the star's light. This increase is measurable.

What is the Doppler Method?

The gravitational interaction between a star and planet results in a "wobble" in the star. These are slight movements back and forth because of an orbiting planet. Astronomers can measure the Doppler shift in the star's light as it wobbles. This is measured based on what wavelengths are visible. The wobble and the change in time allows astronomers to deduce the orbiting planet's period, mass, and distance from the star. (Red shift and blue shift in light)

What is a limitation to wobbling?

The movement is so slight that is can be a challenge to measure. This is not an ideal method.

What is accretion?

The process of tiny particles (that condensed from the nebula) sticking together and forming large objects.

What is the solar nebula theory?

The solar system formed from the nebula (containing hot gas and dust) when it started to collapse. The attraction of the dust particles to one another formed the center and then other dust particles helped to form the planetisimals. Gradually smaller materials kept coming together to form larger objects.

What is the wobbling method?

The wobbling method is measuring the amount of wobbling a star does. A star wobbles when a planet orbit around it because it's gravity pulls on the star a little. This movement is measurable.

Why do terrestrial planets and Jovian planets differ in density?

They differ in density because they differ in composition. Inner planets contain primarily rock and iron. Outer planets contain much lighter materials such as: hydrogen, helium, and hydrogen rich molecules.

Why is Gravitational Lensing such a powerful tool?

This method can even detect low mass objects!

What is the transiting method?

Transiting is detecting a passing planet across a star by measuring the percentage of light that dims. This can reveal the size of the transiting planet. As it passes across, it blocks some of the light emitted by the star. This is measurable.

How do we know that outer planets must have an iron and rocky core?

Two reasons: 1. Outer planets contain approx. the same amount of heavy elements as the Sun so they must have a couple Earth's mass worth of dense materials. 2. Their gravitational fields behave in a way that is best explained by a dense core.

Describe the direction of spin of Uranus

Uranus' rotation axis is at such a great tilt (approximately 90°) that it appears to spin in the opposite direction.

Which two planets do not exactly spin in a counterclockwise direction?

Venus and Uranus

Describe the direction of spin of Venus

Venus' rotation axis is also at such a great tilt that it spins backwards. This motion is called "retrograde rotation". It still orbits in the same direction as the other planets.

What is an example of a large asteroid that is not considered a dwarf planet?

Vesta Because it does not have enough gravity to pull itself into a spherical shape.

Where is the asteroid belt?

between the orbits of Mars and Jupiter