Our Solar System / Study Guide

Our Solar System / Study Guide

What is in the Solar System?

The solar system is made up of the Sun and all of the planets and other objects that orbit the sun.

The Planets

There are eight planets that orbit the Sun, which are divided into inner and outer planets. The four inner planets are Mercury, Venus, Earth, and Mars. The outer planets are Jupiter, Saturn, Uranus, and Neptune.

Dwarf Planets

The Solar system also contains smaller celestial bodies known as dwarf planets. Scientists have identified five dwarf planets: Pluto, Ceres, Makemake, Haumea, and Eris. Scientists believe there may be more than 100 dwarf planets awaiting discovery.

Moons

All planets in the solar system except for Mercury and Venus, have at least one natural satellite, or moon. Earth has just one moon. Jupiter and Saturn each have over 60 moons!

Multiple Choice

What is the largest object in our solar system?

• Jupiter

• Earth

• The Sun

Multiple Select

Which of these planets are inner planets

Multiple Select

Which of these planets are outer planets

Multiple Choice

There are currently five known dwarf planets in our solar system

Distances in the solar system are extremely large, so scientists sometimes measure distances in the solar system in astronomical units (AU). One astronomical unit equals the average distance between Earth and the Sun, which is about 10 million kilometers. The solar system extends over 100,000 AU from the Sun.

Multiple Choice

One AU is the distance between the Earth and the Sun. Which of the following is most likely the distance between the Sun and Mercury?

• 0.39 AU

• 1.0 AU

• 2.67 AU

• 6.0 AU

Multiple Choice

Scientists sometimes write distances in the solar system using _______.

• geometers

• kilograms

• solar units

• astronomical units

• millimeters

Multiple Select

Which of these distances is less than the distance from the earth to the Sun? Select all that apply.

• the distance from the Sun to Mercury

• the circumference of the Earth

• 1 AU

• the distance from the Sun to Jupiter?

Multiple Choice

Which of these distances is the shortest in length?

• the distance from the Sun to Mercury

• the circumference of the Earth

• 1 AU

• the distance from the Sun to Jupiter?

Multiple Choice

Which of these distances is the longest in length?

• the distance from the Sun to Mercury

• the circumference of the Earth

• 1 AU

• the distance from the Sun to Jupiter?

How did the Solar System form?

Scientists believe the solar system formed in a series of steps.

1. A solar

nebular forms

Scientists believe that the solar system formed 4.6 billion years ago from a cloud of gases, rock, ice, and other materials that were pulled together by gravity. The cloud of gas and dust from which the solar system formed is called a solar nebula.

2. The Sun forms

Over time, the solar nebula collapsed, and gravity pulled most of the material toward the center of the nebula. The nebula's temperature and pressure then started to increase and it began to rotate. As it rotated it formed a protostellar disk, which is a large cloud of gas and dust that rotates around a forming star.

The protostellar disk continued to increase in temperature and pressure. The increase in temperature and pressure affected the hydrogen atoms contained in the disk. Eventually, the temperature and pressure in the center of the disk became so high that the hydrogen atoms fused into helium atoms. This process, called nuclear fusion, gives off large amounts of light. Once nuclear fusion began, the Sun started to give off light and beame a stable star.

3. Planetesimals form

While the Sun was forming, small particles of dust, rock, and ice around the disk collided and stuck together. These bodies continued to grow in size and eventually became several kilometers wide, forming planetesimals. A planetesimal is a mass of dust, rock, and other materials that form planets or other objects. over time, the planetesimals collided with each other and stuck together to form the planets and all other objects in the solar system

The planets form

During the solar system's formation, temperatures near the Sun were very hot. This caused much of the water closest to the Sun to evaporate, leaving the planets nearest to the Sun with rocky surfaces and metal inner cores. These inner planets were often small because there was less rock and metal available to form the planets.

The Inner Planets

The smaller masses of these planets meant they had weaker gravitational forces that were not strong enough to pull in lighter gases like hydrogen and helium. Therefore, they are known as the rocky, or terrestrial, planets.

The Outer Planets

Farther from the Sun, temperatures were much colder. This caused ice to form on the outer planets. The ice allowed these planets to have more mass, and they eventually became so large that their gravities could pull in hydrogen and helium. These gases formed atmospheres that are much larger than the inner planets' atmospheres. Therefore, these outer planets are known as the gas giants.

Multiple Choice

A cloud of gas and dust from which the solar system was formed

• protoplanetary disk

• planetesimal

• solar nebula

• protostellar disk

Multiple Choice

A rotating disk of gas and other materials in which the Sun was formed

• protoplanetary disk

• planetesimal

• solar nebula

• protostellar disk

Multiple Choice

A mass of dust, rock, and other materials that forms planets or other objects.

• protoplanetary disk

• planetesimal

• solar nebula

• protostellar disk

Multiple Choice

A rotating disk of gas and other materials in which the planets were formed

• protoplanetary disk

• planetesimal

• solar nebula

• protostellar disk

Multiple Choice

The inner planets formed closer to the Sun in hotter temperatures. What effect did this have on the properties of these planets.

• They formed mostly out of rocks and metals.

• They formed mostly out of gases and ices.

Multiple Choice

The outer planets formed farther from the Sun in colder temperatures. What effect did this have on the properties of these planets.

• They formed mostly out of rocks and metals.

• They formed mostly out of gases and ices.

Multiple Choice

What is a solar nebular?

• a cloud of gas and dust that first formed the outer planets, and then the Sun

• a huge group of stars, star systems, star clusters, dust, gas, and planets

• a cloud of gas and dust from which the solar system was formed

• an explosion that occurs at the end of the life cycle of a massive star

Multiple Choice

What is a planetesimal?

• an object consisting of mostly ice and dust that usually orbits a star in a long, narrow, elliptical path

• a huge group of stars, star systems, star clusters, dust, gas, and planets

• a mass of dust, rock, and other materials that forms planets or other objects

• a relatively large, spherical object that orbits a star and is able to clear the area of its orbit

Multiple Select

Which of these objects are inside of our solar system? Select all that are.

• Mercury

• Saturn's moon

• The Sun

• a far-away star

Multiple Select

Which of these phrases correctly describe the outer planets. Select all that apply.

• mostly ices and gases

• have smaller masses

• have much larger masses

• mostly rocks and metals

• formed farther from the Sun

Multiple Select

Which of these phrases correctly describe the inner planets. Select all that apply.

• mostly ices and gases

• have smaller masses

• have much larger masses

• mostly rocks and metals

• formed closer to the Sun

Multiple Select

Which of these objects can be found inside of our solar system?

Multiple Choice

Gina says that all of the stars in the Milky Way Galaxy are part of our solar system. Is Ginal correct?

• Gina is correct. Our solar system is made up of all the stars in the Milky Way Galaxy.

• Gina is incorrect. Our solar system also includes the stars that are in other galaxies.

• Gina is incorrect. The only star in our solar system is the Sun.

• Gina is incorrect. Our solar system does not include any stars.

Multiple Choice

One astronomical unit (AU) is equal to _______.

• the circumference of the Earth

• the mass of the Sun

• the average distance between the Earth and the Sun

• the average distance between two planets

Multiple Choice

Which is the third step in the formation of the solar system as shown in the chart at left (click to enlarge).

• Planetesimals form

• Nuclear fusion creates a star

• The Big Bang occurs

• Moons form around planets