Q 01/05

Mercury became the smallest planet when which world was reclassified as a dwarf planet?

A) Eris

B) Pluto

C) Makemake

D) Charon

Answer · why

B) Pluto

Pluto was demoted in 2006 after astronomers found comparable worlds such as Eris, leaving eight planets with Mercury the smallest.

Q 02/05

About how long is a year on Mercury?

A) About 3 weeks

B) About 3 months

C) About 1 year

D) About 3 years

Answer · why

B) About 3 months

About 3 months: Mercury laps the Sun every 88 Earth days, so a 30-year-old on Earth would be over 120 in Mercury years.

Q 03/05

A sunrise-to-sunrise day on Mercury lasts about twice as long as what?

A) Its spin on its axis

B) Its own year

C) An Earth month

D) An Earth year

Answer · why

B) Its own year

Its own year: Mercury turns so slowly as it circles the Sun that one side bakes in daylight for a whole Mercury year, then faces a year of night.

Q 04/05

Astronomers long believed Mercury kept one face toward the Sun; what did radar reveal instead?

A) It spins backwards

B) Three spins per two orbits

C) It tumbles chaotically

D) One spin per Earth day

Answer · why

B) Three spins per two orbits

Three spins per two orbits: whenever Mercury was best placed for viewing, it happened to show the same side, which made it look locked.

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.