Mercury

Mercury is the smallest planet in the solar system and the nearest to the Sun, orbiting at an average of about 58 million kilometres. With almost no atmosphere to trap heat, it swings between roughly 430 °C in daylight and −180 °C at night — one of the largest temperature ranges of any planet.

A single day on Mercury (sunrise to sunrise) lasts about 176 Earth days, longer than its 88-day year. Its grey, heavily cratered surface looks much like our Moon, a record of billions of years of impacts.

The table above puts those extremes in Earth units. At 2,439.7 km Mercury’s radius is only about 38% of ours, and 0.055 Earth masses gives a surface gravity of 3.7 m/s² — a little over a third of Earth’s, so the same jump would carry you nearly three times as high. Orbiting at 0.387 AU, it receives close to seven times the sunlight Earth does, which is why the mean surface temperature reads 167 °C even though the night side plunges far below freezing.

With no moons and effectively no atmosphere there is nothing to move heat from the day side to the night side, and nothing to wear down a crater once an impact has cut it. The 176-day solar day against an 88-day year means Mercury turns on its axis so slowly relative to its orbit that the Sun takes two complete years to return to the same point in its sky. Its position changes fastest of all the planets in the 3D solar system simulator, completing a lap while Earth is barely a quarter of the way round.