Q 01/05

What is Europa's surface mostly made of?

A) Basalt

B) Water ice

C) Sulfur

D) Iron dust

Answer · why

B) Water ice

Gerard Kuiper's ground-based observations confirmed the water-ice composition in 1957.

Q 02/05

What is thought to lie beneath Europa's icy crust?

A) A molten lava sea

B) A hollow void

C) A liquid water ocean

D) A solid iron shell

Answer · why

C) A liquid water ocean

Tidal flexing keeps it liquid, and it may hold two or three times the water of Earth's oceans.

Q 03/05

Who discovered Europa in January 1610?

A) Johannes Kepler

B) Galileo Galilei

C) Christiaan Huygens

D) Giovanni Cassini

Answer · why

B) Galileo Galilei

He first saw Io and Europa as a single blur on 7 January and separated them the next night.

Q 04/05

Among Jupiter's four Galilean moons, Europa is which?

A) The largest

B) The outermost

C) The smallest

D) The most volcanic

Answer · why

C) The smallest

It is also the least massive, yet still a planetary-mass moon visible with binoculars.

Q 05/05

Europa is slightly smaller than which body?

A) Mercury

B) Titan

C) Pluto

D) The Moon

Answer · why

D) The Moon

At just over 3,100 km across it is the sixth-largest moon in the Solar System.