1. Jupiter
   Saturn
2. Earth
   Neptune

In 1979, NASA's Voyager 1 spacecraft discovered Jupiter's rings. The rings are made of small, dark particles, which makes them difficult to see without the sun back-lighting them.

1. Venus
   Pluto
2. Earth
   Jupiter

Jupiter has more than twice the mass of all the other planets in our solar system combined. It also has 79 known moons.

1. Dwarf planet
   Meteor
2. Irrelevant
   Baby planet

At approximately 1,400 miles wide, Pluto is half the width of the United States. Its atmosphere is made of carbon monoxide, methane, and nitrogen.

1. Andromeda Galaxy
   Whirlpool Galaxy
2. Sombrero Galaxy
   Milky Way

Currently, the Milky Way and the Andromeda Galaxy are moving toward each other at 250,000 miles. In about four billion years, the two galaxies will collide.

1. Vega
   The Sun
2. Betelgeuse
   Sirius

The sun's temperature varies. On the surface, the temperature is approximately 10,000 degrees Fahrenheit. In the core, the temperature is over 28 million degrees Fahrenheit.

1. Curiousity
   Pioneer 10
2. Voyager 1
   New Horizons

In 2017, Voyager 1 and Voyager 2 celebrated 40 years in space. Both Voyagers carry a 12-inch gold-plated copper disk with sounds and images from Earth.

1. Mercury
   Venus
2. Jupiter
   Earth

Mercury has a metallic core that is between 2,200 to 2,400 miles wide. The core makes up approximately 75 percent of Mercury's diameter, making it the second densest planet in the solar system.

1. Neptune
   Earth
2. Venus
   Jupiter

Venus' surface temperature can reach over 880 degrees Fahrenheit. Venus is so hot because its thick atmosphere makes it difficult for heat to escape.

1. 5 minutes and 30 seconds
   2 hours
2. 8 minutes and 20 seconds
   1 hour, 3 minutes, and 4 seconds

Sunlight takes three minutes to reach Mercury. For comparison, it takes approximately 5.3 hours to reach Pluto.

1. 9
   8
2. 10
   6

The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The International Astronomical Union also recognizes five dwarf plants.

1. Ceres
   Eris
2. Pluto
   Neptune

Ceres is the closest dwarf planet to Earth. It is located in the Kuiper belt, where it is the largest object.

1. Uranus
   Saturn
2. Venus
   Mars

Spirit and Opportunity left Earth in 2004. Once in Mars' atmosphere, Opportunity landed at Meridiani Planum, while Spirit landed at Gustav Crater.

1. Neutron Stars
   Yellow Dwarf
2. Green Dwarf
   Red Dwarf

The sun is referred to as a yellow dwarf. However, this is imprecise. Technically, the sun is classified as a G-type main-sequence star.

1. Approximately every 76 years
   Approximately every 4 years
2. Approximately every 124 years
   Approximately every 51 years

Halley's comet is named after astronomer Edmond Halley. The most recent siting of Halley's comet occurred in 1986.

1. Saturn and Uranus
   Earth and Mars
2. Mercury and Venus
   Mars and Jupiter

The asteroid belt contains millions of asteroids. Most of these asteroids are made of rock and stone.

1. Jupiter
   Neptune
2. Saturn
   Venus

The winds in Jupiter's Great Red Spot peak at around 400 mph. NASA reports that the storm has been shrinking for a century and a half and could possibly disappear.

1. Jupiter
   Uranus
2. Saturn
   Venus

Saturn is a gas giant. It's made mostly of hydrogen and helium. It also has the lowest density of all planets in our solar system.

1. Neptune and Uranus
   Saturn and Jupiter
2. Earth and Mars
   Venus and Saturn

Despite their shared classification, Uranus and Neptune are not believed to have much solid ice. However, NASA thinks there is a massive liquid ocean beneath the planets' clouds.

1. 1
   6
2. 24
   3

The moon's average distance from Earth is 238,855 miles. It's closest distance is 225,700 miles. It's furthest is 252,000 miles.

1. Asteroid Belt
   Interstellar belt
2. Meteor Belt
   Kuiper Belt

Short-period comets start from the Kuiper Belt. These comets take less than 200 years to orbit the sun.

1. Electromagnetic
   Strong Nuclear
2. Weak Nuclear
   Gravity

Not only does gravity keep the moon orbiting around Earth, but it also keeps the Earth and other planets in orbit around the sun. However, gravity gets weaker the more distance there is between objects.

1. Enceladus
   Dione
2. Mimas
   Titan

Titan is the only other body in the solar system that has standing bodies of liquid. In a process much like Earth's water cycle, Titan also has liquids rain from clouds, flow across the surface, and evaporate back into the sky.

1. Comet
   Meteor
2. Planet
   Asteroid

Meteoroids form when a small piece of asteroid breaks off. When a meteoroid survives a journey through the Earth's atmosphere, it becomes a meteorite. Meteors are meteoroids that vaporized in the Earth's atmosphere.

1. Solar eclipse
   Lunar eclipse
2. Earth eclipse
   Regular eclipse

A total solar eclipse happens approximately every year and a half. However, it is not visible everywhere. A partial solar eclipse occurs at least twice a year.

1. Plasma
   Gas
2. Ice
   Rock and metal

Mercury, Venus, Earth, and Mars are the terrestrial planets. They are also the four smallest in the solar system.

1. Earth
   The Sun
2. Jupiter
   The asteroid belt

The Sun is by far the most massive object in the solar system. It contains 99.86 percent of the known mass.

1. Uranus
   Jupiter
2. Neptune
   Mars

Olympus Mons is a large volcano on Mars. It is the largest in the Tharsis Montes region.

1. Uranus
   Jupiter
2. Neptune
   Venus

Jupiter has 67 moons. The largest are Io, Europa, Ganymede, and Callisto.

1. Pluto
   Mercury
2. The Sun
   Venus

Venus has the most volcanoes in our solar systems. It has more than 1,600 known volcanoes.

1. 30 days
   365 days
2. 1,000 days
   1 day

The Earth completes an orbit approximately every 365.5 days. Every four years, an extra day is added to account for the discrepancy .

1. The Sun
   A black hole
2. A solar system
   A belt

Scientists study black holes by examining how strong gravity affects objects around them. If a star and a black hole are close to each other, high-energy light is emitted.

1. Uranus
   Jupiter
2. Mercury
   Earth

Mercury orbits the sun every 88 Earth days. It takes 59 Earth days to rotate on its axis.

1. The Big Bang Theory
   Universal Theory
2. The Milky Way Theory
   Magic

In 1927, Georges Lemaitre suggested that the universe started as a single point. His theory was that the universe expanded in size and could continue to do so. Edwin Hubble discovered the same thing two years later.

1. Mercury
   Uranus
2. Neptune
   Earth

Mercury, Venus, Mars, Saturn, and Jupiter were named after Roman gods. Uranus was named after the Greek god of the sky.

1. Saturn
   Earth
2. Jupiter
   Venus

Scientists believe that Venus initially spun in the same direction as the other planets in our solar system. At some point, Venus' axis flipped 180 degrees, which would explain why its rotation appears reversed.