Q 01/05

Where does Mercury rank in distance from the Sun?

A) First (closest)

B) Fourth (after Mars)

C) Third (after Earth)

D) Second (after Venus)

Answer · why

A) First (closest)

It is also the smallest of the eight planets, smaller even than the moons Ganymede and Titan.

Q 02/05

How long is a year on Mercury, in Earth days?

A) 59

B) 88

C) 225

D) 365

Answer · why

B) 88

Its orbit is the fastest of any planet, which is why the Romans named it after their swift messenger god.

Q 03/05

How long does one solar day (sunrise to sunrise) last on Mercury?

A) About 59 Earth days

B) About 88 Earth days

C) About 176 Earth days

D) About 24 hours

Answer · why

C) About 176 Earth days

That is twice its year: one side bakes for a full 88-day orbit and then freezes for the next.

Q 04/05

Mercury rotates three times for every two orbits of the Sun. What is this relationship called?

A) Chaotic libration

B) Retrograde rotation

C) A 1:1 tidal lock

D) A 3:2 spin–orbit resonance

Answer · why

D) A 3:2 spin–orbit resonance

Astronomers had assumed it was tidally locked, like the Moon, until 1965 radar observations proved otherwise.

Q 05/05

Despite being closest to the Sun, Mercury is only the second-hottest planet. Which is hotter?

A) Venus

B) Mars

C) Jupiter

D) Earth

Answer · why

A) Venus

Mercury has almost no atmosphere to trap heat, whereas Venus is wrapped in a thick greenhouse blanket.