Mercury, the smallest and innermost planet in our solar system, holds many fascinating and unique characteristics. Its proximity to the Sun gives it extreme conditions and unusual orbital mechanics.

Extreme Temperatures

Despite being the closest planet to the Sun, Mercury is not the hottest (Venus holds that title due to its thick atmosphere). However, Mercury experiences the most extreme temperature swings:

• Daytime High: Up to 800°F (430°C)
• Nighttime Low: As low as -290°F (-180°C)

This dramatic difference is due to its thin atmosphere, which is unable to retain heat.

Slow Spin, Fast Orbit

Mercury has a peculiar relationship between its rotation and its orbit around the Sun:

• Year Length: It takes only 88 Earth days for Mercury to complete one orbit (its year).
• Day Length (Rotation): It takes about 59 Earth days for Mercury to rotate once on its axis (its sidereal day).

The table below compares Earth's and Mercury's rotation and orbit times.

The Caloris Basin

Mercury's surface is heavily cratered, similar to Earth's Moon. One of the most notable features is the Caloris Basin, an enormous impact crater:

• Size: Approximately 960 miles (1,550 km) in diameter.
• Formation: Likely formed by a massive impact early in the planet's history.

The Longest Solar Day

Due to its slow rotation and fast orbit, one solar day on Mercury—the time from sunrise to the next sunrise—is extraordinarily long.

• A single solar day on Mercury lasts about 176 Earth days.

Ice at the Poles

Despite the blistering heat on the parts of the planet facing the Sun, scientists have confirmed the presence of water ice inside permanently shadowed craters near Mercury’s poles.

• The floors of these deep craters never receive direct sunlight, keeping them cold enough to maintain the ice.

Exploring Mercury

Only two spacecraft have ever visited Mercury:

1. Mariner 10: Flew past Mercury three times between 1974 and 1975.
2. MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging): Orbited Mercury from 2011 to 2015.