Plutos out -- but are any other planets in? How well do you know our solar system? Take the quiz!


Are you knowledgeable about the other planets, or are you Earth-centric? Take this quiz to find out if you should stay Earth-bound, or if you're ready for infinity ... and beyond.

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Question 1 of 20

Which planet has the shortest day?


... Jupiter completes one rotation on its axis in about 10 hours, even though its diameter is 11 times that of Earth's. And because it's a gas giant and not a solid, Jupiter's equator spins faster than its poles.


Question 2 of 20

How much of our solar system's mass is contained in the sun?

about 30 percent
about 60 percent
about 90 percent
more than 90 percent

... Of all the mass in our solar system, 99.8 percent of it is in the sun.


Question 3 of 20

How long does it take for light to travel from the center of the sun to its surface?

about 8 minutes
about 1 Earth year
about 80 Earth years
hundreds of Earth years

... Although light travels at 186,282.3959 miles per second (299,792.456 kilometers per second), it takes light hundreds of years to move from the sun's center to its surface. The sun is massive, and the light is not moving in a straight line. A lot of particles are colliding, so the light takes a rather circuitous route.


Question 4 of 20

Neptune's largest moon, Triton, sends _______ into Neptune's atmosphere.

carbon dioxide

... Triton has geysers, much like those at Yellowstone Park on Earth. When they erupt, they force ice 5 miles (about 8 kilometers) high, pushing it into Neptune's atmosphere.


Question 5 of 20

Why does Mercury have such a thin atmosphere?

because it does not have an iron core
because it has so little mass
because it's so hot
because in space, no one can hear you scream

... Compared to other planets, Mercury has relatively little mass. Its gravitational pull is not strong enough to bring in much of an atmosphere. In addition, its atmosphere is constantly assaulted by solar winds and blown into space.


Question 6 of 20

Which planet spins in a direction opposite most other planets?


... Venus spins clockwise as you look down from its north pole. The other planets spin counter-clockwise, except for Uranus, which spins on its side. This motion makes it hard to determine Uranus' north and south poles.


Question 7 of 20

What kind of cookie does Saturn's moon Iapetus resemble?

a black and white cookie
an Oreo cookie
a chocolate chip cookie
an oatmeal cookie

... One side of Iapetus appears very dark; the other half is very white.


Question 8 of 20

The moons of Uranus are named after ______.

Greek gods
Roman gods
literary characters
gourmet cheeses

... The moons of Uranus are named after characters in the writings of William Shakespeare and Alexander Pope. Uranus' moons include Miranda (from The Tempest), Titania (from A Midsummer Night's Dream) and Umbriel (from The Rape of the Lock).


Question 9 of 20

Who was the first woman in space?

Sally Ride
Svetlana Savitskaya
Valentina Tereshkova
Ellen Ripley

... In 1963, Valentina Tereshkova of the Soviet Union became the first woman in space. Sally Ride was the first American woman in space in 1983. Svetlana Savitskaya became the first woman to walk in space on July 25, 1984.


Question 10 of 20

What is the hottest planet in our solar system?


... Venus has an incredibly thick atmosphere; it's primarily carbon dioxide. (Think greenhouse effect.) The sun's rays enter and become trapped. The atmosphere of Venus has an average temperature of 875 degrees Fahrenheit (468 degrees Celsius). Mercury only rises to about 800 degrees Fahrenheit (427 degrees Celsius).


Question 11 of 20

If our solar system were the size of a quarter, how big would the Milky Way galaxy be?

the size of a silver dollar
the size of Ireland
the size of North America
the size of our moon

... If our solar system were as tiny as a quarter, the vast Milky Way galaxy would be as large as the entire North American continent.


Question 12 of 20

About how many moons are orbiting planets in our solar system?

about 50
about 150
about 1,000

... About 150 moons orbit the eight known planets in our solar system. This does not count any circling dwarf planets. There are about 20 more orbiting objects still waiting to be officially declared "moons."


Question 13 of 20

Which planet would float in a bathtub (if you had a tub big enough)?


... Saturn's density is 0.687 grams per cubic centimeter. The density of water is 1 gram per cubic centimeter.


Question 14 of 20

What are Jupiter's rings made from?

Jupiter doesn't have rings.

... Jupiter's rings are hard to see; they were first noticed during the Voyager 1 expedition in 1979. The rings are made from the dust that arises as meteors strike Jupiter's moons. The dust orbits the planet.


Question 15 of 20

If you weighed 160 pounds (72.6 kilograms) on Earth, how much would you weigh on the sun?

about 80 pounds (36.3 kilograms)
160 pounds (72.6 kilograms)
about 1 ton (907.2 kilograms)
about 2 tons (1,814.4 kilograms)

... If you weighed 160 pounds (72.6 kilograms) on Earth, you'd weigh 4,331.5 pounds (1,964.7 kilograms) on the sun because of its strong gravitational force.


Question 16 of 20

If you could drive a car around one of Saturn's rings at 75 miles per hour (120.7 kilometers per hour), how long would it take?

less than one day
less than one year
about 10 years
about 100 years

... If you could speed around a ring of Saturn in your sports car, it would take 285 days.


Question 17 of 20

What are colder areas of the sun called?

solar flares
dark shadows

... Sun spots appear as dark areas on the sun, the size of planets. They are only about 6,700 degrees Fahrenheit (3,704 degrees Celsius), compared to the area around the sunspots, which are 10,000 degrees Fahrenheit (5,538 degrees Celsius).


Question 18 of 20

About how big across is Pluto?

twice the size of our moon
half the size of Mars
half the size of Earth
half the size of the United States

... Pluto, the dwarf planet, is only 1,400 miles (2,253 kilometers) across -- less than half the 2,900 miles (4,667 kilometers) of the contiguous United States.


Question 19 of 20

About how big is our solar system?

about 1 billion miles (about 1.6 billion kilometers)
one astronomical unit
2 light years

... According to scientists, the size of our solar system depends upon the sun's gravity, which extends for almost 2 light years.


Question 20 of 20

Besides our own, how many solar systems are there within the Milky Way Galaxy?

about 6,300
about 2 million
about 1 billion

... Astronomers do not know how many other solar systems are within our galaxy. There are about 200 billion stars in addition to our sun. Planets themselves don't shine, and they don't reflect light very well, so it's hard to see them orbiting distant stars.


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