Mercury

Type: Terrestrial planet
Mass: 3.3 × 10^23 kg
Position in the Solar System: 1
Distance from the Sun: 60 million km

Mercury is the least massive and closest planet to the Sun, making it particularly difficult to observe from Earth. The easiest method is to observe it in transit, when it passes in front of the Sun.

Fun fact: Due to its slow rotation and highly eccentric orbit, a sunrise on Mercury can sometimes… interrupt itself and go backward before resuming its normal course. A unique cosmological phenomenon!